Lupine Publishers | The Dental Service of the French Army in 1940

 Lupine Publishers | Journal of Dental and Oral Health Care

Brief Historical Summary

On December 1 1892, the Brouardel law was voted which gave legal status to dental surgeons. At that point, those who had followed appropriate studies delivered by the Faculty of Medicine were the only ones who could practise dental surgery [1]. Therefore, it was a profession in its infancy which enlisted during the war in 1939? On February 26 1916, a dental service was created in the infantry within the French army for the duration of the war. That of the Navy only started on March 1st 1916. After the Great War, only the Navy decided to dissolve its dental service for it did not have a satisfying organization to greet its patients. In 1934, a backup dental service was implemented once again. While they were made lieutenants in 1818, dentists could become captains after the law voted on December 19 1934 [2]. A few months later, dentists in the land army were attributed the same rank.

National Federation of Reserve Dental Surgeons (Federation Nationale Des Chirurgiens-Dentistes De Reserve - Fncdr)

In 1925, the first dental officers who returned to civil life assembled to form the Association of dentists of the land army, the navy and the air force from the Paris region during the 3rd Congress of medicine and military pharmacy. It was aiming at keeping the ties they built during the war and at helping each other to get back to normal life [3]. A two-year optional superior military training was created. Once students in dental surgery had passed it, it allowed them to accomplish the very last part of their military service as 2nd class military dentist which was a rank similar to that of second lieutenant. Then, they joined dental care garrisons, centres for edentulous patients or even centres for maxillofacial prosthodontics. In 1927, there were only eight of them. Those who had not passed their two-year optional superior military training were only able to join the nursing unit [4,5].

Thereafter, these associations asked the Minister of War and of National Defence the permission to open an advanced level training school for dental surgeons called EPOR. The central administration of the French Defence Health service (Direction centrale du Service de santé des armées -DCSSA), who was in charge of diversifying the health service’s branches, immediately supported the initiative which led to the opening of the first EPOR. This training school offered its first services during the monthly lectures of the Villemin military hospital on October 1926. From 1931, the initiative taken by Paris spread over the country and each military region could benefit from their own EPOR. Moreover, integrating this school soon became a prerequisite to get an upper grade [6].

In 1933, all those regional associations eventually gathered into a National federation of Reserve Dental surgeons which was notably later chaired by Pierre Budin who was one of the eleven chairmen of the federation and who received the Legion of Honour in 1920 for his bravery on the battlefield. This institution thoroughly devoted itself to the improvement of the dentists’ status. The DCSSA organized the dental surgeon’s training in order to get them ready for all sorts of duties: anaesthetists, surgical assistants, radiologists, first-aid workers, etc. It was Pierre Henry’s case who was mobilised in 1940 and who joined the surgical team of the Ancemont Hospital where he practised as anaesthetist. During the war, as he was demobilised, he practised in Rennes [7]. It was in this way that, in the Val-de-Grâce Hospital, the general practitioner Ginestet trained dental surgeons to specialties of maxillofacial surgery. The dentists were informed on various medical practices with respect to the damage caused by more modern weapons and which led to more complex and numerous maxillofacial injuries. All that work which was organised with the help of the DCSSA prepared the intervention of the dental surgeons’ corps in the event of future conflicts [4,5].

Active Dentists

The French Defence Health service which included the dental surgery service reshaped its organisation following the assessments which were carried out at the end of World War I. It decided to implement more mobile structures which aimed at following a regiment or a division or which were able to adapt to the new schemas of so-called movement wars. Therefore, mobile surgical groups, advanced hospitals, medical hospitals of evacuation and various health services appeared. Within each of these structures, one or two dentists were incorporated. Through Article 39, the law of April 1 1923 planned that dental students had to accomplish their military service in the health service as nurses if they had not finished their dental curriculum or as second class dental surgeons if they had graduated [7].

Mobilisation

World War II broke out on September 3 1939. Everybody mobilised in France. Reserve dental surgeons were called upon as lieutenants for the most of them on different strategic areas. They were either assigned in the sanitary formation of the divisions, in the surgical ambulances or in the front regiments. At the beginning of the war, they barely practised dentistry. They mainly served as assistants for specialised medical treatments. Only a few practised in the garrison dental surgeries or in those of hospitals. Indeed, with the growing mobilisation, the Health service created dental surgeries in each area settlements and in the most important garrisons. Thus, in the front, they intervened in aid stations to cure the wounded. In divisional areas, they collaborated with doctors and surgeons within mobile or advanced surgical groups. Finally, at the rear, they were employed by maxillofacial centres or by radiology services. At the beginning of the war, immediate interventions and first-aid treatment had priority and demanded a lot of efforts especially as the bombing victims were not only soldiers but also civilians. Those who had followed the teaching delivered by the EPOR were more easily assigned in surgical services [6].

(Delivered) Treatment

Curing the soldiers’ oral pathologies, soothing their pain and quickly making them operational was a primal objective. A man who is in pain does not fight right and immediately constitutes a threat for his comrades. Furthermore, a person with bad teething cannot chew properly which can lead to other general diseases. Seeing the soldiers and being among the troops also allowed the dental surgeons to deliver notions of oral hygiene. A schematic note was written for each soldier in order to keep track of his treatment and the head of the dental surgery also used to write reports on a daily basis. On them were written all the consultations and carried out interventions. Reconditioning oral cavities was systematically carried out before each military operation with a compulsory preliminary tartar removal which was the first hygienic approach. Numerous dental extractions were carried out. Each attribution of a prosthetic device had to be subjected to the approval of the head of the Regional Health Service through the main stomatologist’s intermediary.

Once the head of the dental surgery gave his approval the extractions were made before the making of a device. A month and a half later, the device could be made. On the contrary, if the making was refused, only extractions were made [6]. In each dental surgery, the staffs was made up of a department head who often was a stomatologist or a military dental surgeon and of military dental surgeons to assist him according to the needs decided by the main regional stomatologist. This department head was under the supervision of the chief doctor of the training to which he was linked such as the corps troops, the regimental infirmary, the military hospital, etc., while being under the main stomatologist’s command [7]. In 1940, continuing education was insured thanks to magazines such as “Odontologie” which ended its publication between June/ July 1944 and March/April 1945. In 1942, the publications spread for lack of promoting advertisement and because of the war, and eventually diminished until they did not get enough cover.

Stomatology Service

During World War II and after the French surrender which was signed in Rethondes on June 22 1940, numerous demobilised dental surgeons were called upon to treat soldiers who were wounded in the face. This was when maxillofacial surgery became extremely important in terms of medical care. It became a full-fledged specialty which benefited from new techniques and materials. Stomatology services existed along the secondary organisations such as the garrison dental surgeries which operated in each area settlements and in the most important garrisons. They were implemented at the beginning of the war.

There were two different articulations concerning the rear structures:

Inter-Regional Technical Services

The inter-regional centre of surgery and of maxillofacial prosthetics was independent from the regional service but was under the supervision of the chairman of the regional health service which it was a part of. A surgeon, head of department, was at its head and benefited from a stomatologist’s assistance who was leading the maxillofacial prosthetics service. As a team, they could rely on all the specialists and dental prosthetics technicians. In these inter-regional centres, they mainly treated damaged maxillary bones as well as those of the face and the neck thanks to this coeducational surgical and stomatological training. On the contrary, simpler maxillary fractures, that is to say those without a loss of substance, were treated in the regional stomatological centres. Likewise, simple edentulous patients were not accepted in surgical and stomatological centres. Centres for edentulous patients were implemented for the wounded that could be fitted with prosthesis. Each centre was specialised. The main objective was to quickly orientate the wounded.

Regional Technical Services

Only one stomatology service existed in a region. In the event of a big region, there could be more of them. Only one centre of dentures for edentulous patients worked to making the dentures of all the edentulous people who came in the dental surgeries of the local garrison. Those local stomatology and dental prosthetic services contained from 50 to 100 beds out of a total of around 10,000 and 20,000 beds for the entire medical sector. The odontostomatologic illnesses too important to be treated in the dental surgeries, the dental illnesses, simple maxillary or prosthetic fractures, and surgical extractions were operated there. The simple fitting of prosthesis on edentulous people was also carried out there. The management of regional centres was insured by the main local stomatologist. He had to keep a close watch on the stomatology and dental prosthetic centre, and dental surgeries. Here was his staff:

i. A dental prosthetist who was able to make a set of dentures per day, that is to say 30 dentures per month;

ii. A military dentist who was able to provide the same work than that of 4 out of 5 technicians.

Figure 1: Dental surgery in Fort Hackenberg-Maginot line (20 km away from Thionville, Mozelle).

Figure 2: Dental surgery in Four à Chaux, Vosges.

Figure 3:

An officer was in charge of the management of the equipment which included the maintenance and the stock according to the wants and needs. He also kept a log of which was fitted in the patients ‘mouths with the description of the device. This allowed justifying the price of each set of dentures. Finally, the local head could subsequently follow the activity of the centre for edentulous patients thanks to a monthly report [8]. The ability training of the military service of December 7 1938 for metropolitan troops included a calculation giving the soldier’s chewing coefficient. In case of a lack of needed dentures, the fitting was made possible only if the soldier’s chewing coefficient was lower to 25%. Therefore, each fully edentulous man could receive a full set of dentures and could be kept in the service (Figures 1-3).

In case of maxillofacial emergency, the wounded soldier had to be driven to a maxillofacial centre from two to ten days after the injury. The quicker the treatment started the better were the chances of recovery. As for the repairing phase, it often needed transplants. The immobilisation of fractured bony edges was essential to be successful. The average period of the primary consolidation of transplants was of around two months but it was only around the fourth month that the transplants looked normal again. On November 11 1942, the German army invaded the free zone, France’s Southern part. A month later, Vichy’s “Armistice Army” was disbanded. Hence, the French Defence Health service no longer existed. Any medical support was entrusted to the British and mostly to the Americans during the conflict. In 1940, numerous demobilised dentists put up resistance, their dental surgeries often served as turntables for the exchange of information. Many of them were shot by the Gestapo [9]. Many others were deported and came back weakened from the camps (René Maheu)(Figure 4). Some others enlisted in the Free French Forces (Maurice Prochasson). Dental lieutenant’s uniform (purple velvet on the flat-topped French military cap, on the collar tips, the caduceus was visible on each collar tips and buttons), made between 1930 and 1935, worn in 1940, the khaki military cap was made from 1930. Before it was blue (Figure 5).

Figure 4:

Figure 5:

Figure 6:

The braids were on the turn-ups during World War I. They were above the turn-ups from 1934/1935. Here, on the picture, they are on the turn-ups. The dental officer’s uniform was similar to that of the cavalry (executive order 1934)(Figures 6 & 7). Here, it was prior to 1934. Among the decorations, from left to right, the following ribbons are recognisable:

Figure 7:

i. Knight of the Legion of Honour.

ii. 14-18 Cross of War (without mention in despatches).

iii. Combatant Cross (created following the law of June 28 1930).

Figure 8: Pierre Audigé (1908-1944) (Audigé Family, 2005).

iv. Impossible to identify, but given the order of wearing official French decorations, it could be the Allied Medal (or Victory Medal) created following the law of July 20 1922 and which was granted provided three successive months or not of presence between August 2 1914 and November 11 1918, to the soldiers belonging to the units enumerated by the ministerial instruction of October 7 1922, which is worn before distinction (Figures 8-11).

Figure 9: Alain Maheu (1899-1980) back from deportation (Maheu, 2003).

Figure 10: Maurice Prochasson (Museum of the Order of the Liberation, 2011).

Figure 11: A soldier wounded in the face upon his arrival (left) and his departure (right) of the African centre (Converse J., Péri M. & Roche G. K. T., 1944).

v. Médaille commémorative française de la Grande Guerre

vi. The Insignia for the Military Wounded. The trousers have a command band which existed from 1830 [10-13].

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Lupine Publishers | Synthesis and Characterization of Poly (1,4-Benzenedimethylene Phthalate) and the Study of its ability to sorb Pb(II), Cd(II), and Zn(II) ions

 Lupine Publishers | Journal of Organic and Inorganic Chemical Sciences

Abstract

Poly (1,4-benzenedimethylene phthalate) was synthesized by condensation of phthaloyl chloride with 1,4-benzenedimethanol in the presence of pyridine in dry THF at 30 °C . The resulting polymer white powder was characterized by viscosity measurement, FT-IR, 1H and 13C NMR, elemental analysis, thermal (TGA-DSC) methods and scanning electron microscopy. The uptake properties of Pb(II), Zn(II) and Cd(II) metals by the polymer from aqueous solutions were studied by the batch and column techniques as a function of pH, temperature, concentration and contact time. The uptake increased with increasing pH reaching a maximum at pH = 6.00 for all ions. The polymer showed high uptake capacities toward Pb(II) and Zn(II) ions, but medium uptake capacity toward Cd (II). The linearized forms of Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms indicate studied ions Pb(II), Zn(II), and Cd(II). The adsorption capacity follow the order: Pb(II) > Zn(II) > Cd(II).

The thermodynamic functions, ΔGǂ, ΔHǂ and ΔS° were determined for Pb(II), Zn(II) and Cd(II); the values of AG° indicated that the adsorption process of these metal ions on the polymer is favorable. In this work, the values of ΔGǂ, ΔGǂ and ΔSǂ were determined by using Eyring-Polanyi equation and Arrhenius equation. The results indicated that ΔGǂ=72.8, 78.6, 87.8kJ/mol for Pb, Zn, Cd ions, respectively. The column experiments for metal ion uptake were conducted at pH= 6.0, 25.0 °C, and initial concentration of 150.0mg/L. The loaded concentrations were 76.42, 49,05 and 28.47 ppm for Pb, Zn, Cd ions, respectively. The efficiency for recovery of metal ions after adsorption by treatment of the loaded polymer with 0.1M HNO3, 0.1M EDTA, gave good percent recovery for 0.1M HNO3

Keywords: Benzendimethanol; Phthalate polymers; Condensation polymerization; Polymers uptake; Metal ion uptake; Adsorption

Introduction

Heavy metals are known for their toxicity to living organisms. Their concentrations in the environment increase with the increase of industrial activities. Most important, these metals are not biodegradable and tend to accumulate in living organisms, and causes serious health problems [1]. Allot of methods were reported for removal of metal ions from aqueous solutions; these include filtration, adsorption, chemical precipitation and ion exchange [2]. Different approach for removal of metal ions from water streams which have been increased in recent years [3], is the adsorption of metals by polymers. This approach is characterized by high effectiveness, high adsorption capacity, and high selectivity, fast kinetics of metal-ion uptake, high mechanical strength, chemical resistance and recyclability of the polymer [4,5].

According to their methods of preparation, synthetic polymers can be divided into three major types:

A. Chain Reaction (Addition) Polymers: These polymers are formed by addition to the double bond of monomers containing carbon-carbon double bonds, called vinyl monomers, without the loss of small molecules. The repeating units of addition polymers have the same composition as the monomer [6].

B. Condensation Polymers: these polymers are formed by condensation reaction of monomers containing organic functional groups. These reactions usually involve elimination of small molecules (e.g., water, methanol, and ethanol) [6].

C. Other Polymers May Be Prepared by Modification of Polymers by: I- Attachment of an appropriate specific ligand groups to the polymer chains. This method has been preferred since functional groups containing ligands can easily be attached to polymers than inorganic supports. [7,8]f The attachment of dithiocarbamates to polystyrene cross linked with 2% divinylbenzene is an example of this type [9]. II- Polymerization of monomers to which ligand groups are attached. Polymers with ester linkages in their main chain are used in many applications such as biomedical matrices, liquid crystals, fibers, and heat resistant materials [10]. Polyesters are characterized by higher adsorption capacities, efficiencies as well as high selectivity to some metal ions. [11] Synthetic polyesters may be prepared by polycondensation of diacids with diols, diaciddichlorides with diols and ester interchange reaction of diesters with diols.

There are two types of polyesters: Aliphatic polyesters and aromatic polyesters. The synthesis of aliphatic polyesters has been well established for several years. However, these polyesters possess low thermal stability due to their low melting points and glass transition temperatures owing to their low molecular weight. These properties resulted in limited usage and few applications of aliphatic polyesters, yet they showed potential as biodegradable polymers. On the other hand, aromatic polyesters display an excellent pattern of physical properties. They are strongly resistant to hydrolysis, bacterial and fungal attack, they also remain unaltered in the environment [11,12], Combining aromatic and aliphatic units in the same polyester chain has been envisaged as an attractive approach to obtain novel products encompassing biodegradability and high performance properties [11].

There are a lot of polymers were prepared and their sorption behavior was studied in our laboratory,such aspoly (1,4-cyclohexanedimethylene oxalate), Poly (bisphenol A oxalate), poly-cis,trans (1,3-cyclohexylene oxalate), poly (bisphenol- Aphthalate), poly (bisphenol-Acis-1,2 cyclohexanedicarboxylate), poly (1,4-yclohexanedimethanolphthalate) and poly (1,4-cyclohexanedimethanol succinate).

Experiment

Materials

The chemicals were obtained from commercial sources as either analytical reagent grade or chemically pure grade and were used as received. The chemicals were purchased from the corresponding companies: Phthaloyl dichloride, 1,4-benzenedimethanol, cadmium(II) nitrate tetrahydrate and zinc(II) nitratehexahydrate from BDH; N,N-4-dimethylaminopyridine (4- DMAP), dimethylsulfoxide (DMSO) from Acros, pyridine (GPR), nitric acid (65%), hydrochloric acid (36.5 %), and disodium ethylenediaminetetraacetate(EDTA)(Scharlau), sodiumperchlorate (SIGMA), tetrahydofuran (THF) (GCC) and lead(II) nitrate (PRS Paureac) and 4-dimethylaminopyridine (4-DMAP)from Acros.

Preparation of The Polymer

Poly(1,4-benzenedimethylenephthalate) was synthesized by polycondensation using single phase organic solvent polymerization. 1,4-benzenedimethanol ( 4.97g, 0.036 mol), pyridine (8.54g, 0.108mol) and a catalytic amount of 4-DMAP were dissolved in THF (60 mL). To this solution, a solution of phthaloyl chloride (7.307 g, 0.036mol) in THF (30mL) was added drop wise with stirring. The reaction mixture was stirred for 1 h at (30-35) oC and then for 3 days at room temperature. The polymer precipitated as a white solid from the THF solution. The solvent was evaporated and the solid was dissolved in chloroform (150mL) and washed with water (2x500mL), (6% v/v) HCl solution (1 x 150mL), and finally with distilled water (3x500mL). The chloroform solution was dried over anhydrous sodium sulfate, and was then concentrated to about 100 mL of solution. The polymer was precipitated by drop wise addition of chloroform solution to 500.0mL of methanol. The precipitated polymer was then filtered and dried at 55.0 oC under vacuum to give a white powder 66.0g, (68 % yield).

Preparation of Stock Solutions

Stock solutions (1000.0 mg/L) of the three metal ions were prepared by dissolving specific amounts of the salts of Pb(II), Zn(II), and Cd(II), in 0.1 M NaClO4 which was adjusted to the desired pH. The stock solutions were used to prepare solution with different concentrations (20.0, 40.0, 50.0, 60.0, 80.0, 100 and 150.0mg/L). The dilution is achieved by using 0.10 M NaClO4 and adjusted by 0.10 M HClO4 to achieve the desired pH= 4.00, 5.00 and 6.00.

Study of Metal Uptake Characteristics of The Polymers By Batch Technique

The metal uptake characteristics for each metal ion were studied using batch equilibrium technique. An aqueous solution of known metal ion concentration (25.0mL) was added to polymer powder (0.10 g), the mixed solutions were mechanically shaken, after a certain period of time at 25.0 oC, 35.0 oC, 45.0 oC, the mixture was filtered and the amount of the metal ion remaining in the filtrate solution was determined by atomic absorption spectrometry after constructing up an analytical calibration curve for each element (Pb(II), Zn(II), and Cd(II)).

The Rate of Metal Ion Uptake

Experiments for determining the equilibrium time for the metal ion uptake process involving 100.0mg ± 0.1 mg of the polymer was swelled with 25.0mL of metal ion solution containing 150mg/L metal ion at different pH, and the solution was mechanically shaken. The contact time was varied from 5 minutes to 48 hours at 25.0 oC, 35 oC, 45 oC. The mixture was filtered and the amount of the metal ion remaining was determined with atomic absorption spectrometry. The amount of metal ion uptake by the polymer (qe), may be obtained from the following relation:

q_e: Metal ion uptake by the polymer (in mg M(II)/ g polymer).

C_i: Initial metal ion concentration (mg/L).

C_eq : The residual concentration of the metal ion in solution at equilibrium (in mg/L).

V: volume of solution (L).

m: mass of polymer (g).

And the percentage of metal ion loading by the polymer expressed as % uptake was [13]:

Effect of pH on The Metal-Ion Uptake

Similar experiments were also carried out, under different pH values of 4.00, 5.00 and 6.00 for fixed contact time of 24 hours to determine the effect of pH on the metal ion uptake by the polymer.

Adsorption Isotherms Studies

The adsorption of Pb(II), Zn(II), and Cd(II) was carried out by taking a known mass of 100.0g ± 0.1mg of the polymer swelled with 25.0mL of solutions of concentration variation ranging from (20.0- 150.0)mg/L for each metal, under different pH values of 4.00, 5.00 and 6.00 and different temperatures (25.0, 35.0 and 45.0) oC.

Metal Ion-Uptake By The Polymer Using Column Experiment

Glass column of 30.0 cm length and 1.5cm inner diameter was used in this experiment. The column was packed with 1.00g ± 0.1mg dried polymer. A sample volume of 150.0mL containing Pb(II) of 1000mg/L was passed through the column at a flow rate of 1.0mL/4min. The eluate was collected in a 100.0mL volumetric flask, and concentration of the metal ion was then determined by AAS. The same experimental conditions were used for the determination of Zn(II), and Cd(II) ions uptake, where the sample which passed through the column was 150mg/L of these metal ions.

Desorption studies

The desorption of the Pb(II), Zn(II), and Cd(II), ions was carried under column condition, where the polymer was loaded with each metal ion as described before, using 50.0mL of two eluting agents, 0.10M HNO3 and 0.10M EDTA were used for polymer recovery from adsorbed metal ion, keeping the flow rate of elution at (1mL/4min). The concentration of metal ion in the eluate was collected in five 10.0mL portions, and was then determined by AAS.

Water regain (α):

Water regain is defined as the amount of water absorbed by 1000.0mg ± 0.1 mg of polymer [14]. A sample of dry polymer was suspended in water, and was left for 2 and 24 hours. The polymer was filtered and weighed, dried at 60.0 oC and then re-weighed. Water regain (α) was calculated from the mass difference (eq).

Results And Discussion

Polymer synthesis

The synthesis of poly (1,4-benzenedimethylene phthalate), from equimolar amounts of 1,4-benzenedimethanol and phthaloyl chloride was performed by solution polycondensation in THF at 30.0 °C in the presence of excess pyridine as acid scavenger and 4-DMAP as the catalyst. The reaction proceeded by pyridine- catalyzed nucleophilic displacement of the chloride of the phthaloyl chloride with the alcoholic group of 1,4-benzenedimethanol. The relatively high yield of the polymer may have been due to the high reactivity of phthaloyl chloride group. The resulted polymer, which was obtained as a powder was found to be insoluble in many common organic solvents such as tetrahydrofuran (THF), diethyl ether, acetone and methanol but soluble in chloroform.

Solution viscosity

The inherent viscosity of poly(1,4-benzenedimethylene phthalate) solution was calculated from viscosity measurements of dilute polymer solutions (0.5g/dL) in chloroform at 25 °C. The polymer had an inherent viscosity of 0.22dL/g. This value indicates that the polymer had an intermediate inherent viscosity which implies that it had moderate molecular masses. This value is higher than the those obtained at 0-5° for poly(bisphenol-Aphthalate), poly(bisphenol-Asuccinate), and poly(cyclohexanedimethylene phthalate) which had the values of 0.11dL/g , 0.13dL/g, and 0.11dL/g, respectively [15].

Infrared spectroscopy

The polymer was analyzed by FT-IR spectroscopy. The FT-IR spectrum exhibits characteristic absorption bands for the major bonds involved in the polymer. The FTIR spectrum (Figure 1) showed two strong absorption bands for the stretching vibration of the carbonyl group (C=O) of the phthalate ester group at 1726cm-1 and for C-O-C in the range from 1124 to 1279cm-1. Another strong IR band was observed at 2951cm-1 assigned to the C-H stretching in the 1,4-benzendimethanol moiety. These wave numbers, which are typical for the ester group are conformed to the reported literature [15], and thus confirm the formation of the postulated polymer Scheme 1 and Figure 1.

Scheme 1: Preparation of poly (1,4-benzenedimethylene phthalate) polymer.

Figure 1: IR spectrum of poly(1,4-benzendimethayl phthalate) polymer.

The Nuclear magnetic resonance (nmr) spectra for polyesters

Figure 2: 1H-NMR spectrum of the polymer.

1H-NMR spectrum: The polymer was analyzed by NMR spectroscopy in order to elucidate its chemical structure and support its formation. In the 1H-NMR spectrum of poly(1,4- benzendimethylene phthalate), the signal of the aromatic protons of the phenylene ring of benzendimethylene unit was observed as singlet at δ = 7.36ppm, whereas that of the aliphatic methylene protons attached to the oxygen of the ester group was observed as singlet at δ = 5.22ppm. The aromatic methylene protons of the phthalate unit in ortho and meta positions to the ester were observed at δ = 7.71ppm and 7.50ppm, respectively. The 1H-NMR spectrum is shown in Figure 2. In the 13C-NMR spectrum of poly(1,4- benzendimethylene phthalate), the signal of the aromatic carbon atoms of the phenylene ring of benzendimethylene unit appeared at δ = 129ppm. The signal of the quaternary aromatic carbon atoms appeared at δ = 136ppm. The signal of the aliphatic methylene carbon atoms attached to the oxygen of the ester group appeared at δ = 67ppm. The signal of the quaternary aromatic carbon atoms of the phthalate unit to which the ester group is attached appeared at δ = 132ppm. The signals of the aromatic carbon atoms in ortho and meta positions to the ester group appeared at δ = 129ppm and 133ppm, respectively. The signal of the carbonyl carbon atom of the ester group appeared at δ = 167 ppm. The 13C-NMR spectrum of the polymer is shown in Figure (2), and the1H-NMR and 13C-NMR spectral data for the polymer assigned to the various proton and carbon atoms are presented in Table 1 (Figures 3 & 4).

Figure 3: ¹³C-NMR spectrum of the polymer.

Figure 4: DSC thermo gram of polymer.

Table 1: Thermal stability of polymer.

Thermal Properties

The thermal properties of polyesters synthesized were also investigated by differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) under dry N2 atmosphere.

Thermal Transition

The thermal properties of polymer were investigated with DSC and TGA. The Tg value of the polymer was 52°C. This value is considered lower than expected for such an aromatic polymer such as poly(ether carbonate) containing aromatic -aromatic ether showed Tg values from room temperature up to 47°C [16] and polyquinoxalines and other aromatic polymers were studied Tg from 215.5 to 394.5°C [17]. This Tg value may have been due to the imparted flexibility effects of the aliphatic methylene groups of the 1,4 -benzenedimethanol. The presence of the aliphatic moieties in the polymer backbone imparted flexibility to polymer segments to move under the effect of temperature. This ease of motion is reflected in the slightly low Tg value of the polymer [16]. The DSC thermogram of the polymer is shown in Figure 4.

Thermal stability

The thermal stability of the polymer was investigated by TGA under dry nitrogen. Table 1 summarizes the initial thermal decomposition (onset) temperature Tid, T⁵%d , T¹⁰%d , and T⁵⁰%d decomposition temperatures, which correspond to the temperatures at which 1, 5, 10, and 50% loss of mass of polymer occurred, respectively. The table 2 also shows the residual mass percent remaining after heating the polymer to 673.1 °C which was found to be 8.74%. The thermogram of the polymer Figure 5 displayed a typical one-stage characteristic with a relatively fast mass loss occurring at temperatures between 400 and 450 °C. The fast mass losses may have been due to decomposition of the polymer backbone. These values are higher than the corresponding values obtained in the case of poly (1,4-cyclohexandimethlene- phthalate), which occurred between 350-450°C and the residual mass equal 0.44% [15].

Table 2: Several reported metal uptake values by chelating polymers in the literature.

Figure 5: TGA thermogram of poly(1,4-benzenedimethayl phthalate) polymer.

Morphological Characterization

The surface ofthe polymer was also characterized by SEM before and after metal sorption. The SEM micrographs for the polymer synthesized are shown in Figure 6. The pores are distributed on the rough surface of the polymer, the small pores which are similar to the forms of flowers are located on the surface of the rods with an average size <5|im. The existence ofthese pores provides convenient diffusion channels for metal ions into the interior of the polymer when it is used for adsorption of metal ions from aqueous solution. The interior structure of the polymer showed randomly distributed large gaps and air pockets created during polymerization. The spongy structure of the inner rods maximize the contact surface between the polymer and the solution which led to increased metal ion uptake, this is shown in Figure 6a for the polymer before metal sorption. However, after adsorption of metal ion by the polymer, a slight loss occurred to the composition of surface features and of the channel and a small part of its surface became smooth. This is represented for the polymer surface loaded with Cd(II) ions and is shown in Figure 6b & c. It has been found by SEM investigation that loading the polymer with zinc ions changed its surface topography, increased the proportion of smooth surface and resulted in narrow channels and pores Figure 6d & 6e. The highest uptake of metal ions by polymer was for Pb(II), the polymer loaded with lead ions was studied by SEM to observe the changes in surface topography that took place, the entire surface became smooth and the pores disappeared due to full metal ion coverage. SEM for our polymer was similar to that of poly(cychlohexandimethelen succinate) (Al- Dweri, 2010). The images are presented in Figure 6f-6i.

Figure 6: SEM images of poly(1,4-benzenedimethelen phthalate).

Water Regain or Water Content ( α )

Water regain experiment was performed to determine the water regain ratio (α) for the polymer. Water regain is usually correlated with the hydrophilic character of the polymer, the higher the water regains, and the more hydrophilic the polymer is. The water regain value for the polymer was found to be 0.019 g/g after 2h of stirring and 0.029g/g after 24h stirring, this indicates that the polymer has a low hydrophilic character. These values are higher than the corresponding values obtained by poly(1,3-cyclohexylene oxalate) polymer which was found to have values of 0.011g/g and 0.014g/g, respectively. Based on these values the polymer is considered to be low hydrophilic in nature [18] and these values are smaller than the corresponding values obtained for poly (1,4-cyclohexanedimethylene oxalate) polymer which was found to have values of 0.064g/g and 0.087g/g [19]. Principally, the water molecules are polar and would interact with the polar groups of the polymer (the ester group), this interaction explains the water regain properties of the polymer.

The rate of metal ion uptake by the Polymer

The adsorption kinetics of metal ions on the surface of the polymer was investigated as shown in Figure 7 for example. The adsorption of metal ions increase with time until complete saturation.

Figure 7: Metal uptake as a function of contact time, at pH = 6, T = 45 °C, and initial concentration of 150ppm.

Adsorption Isotherms of the Polymer

Using linearized Langmuir and linearized Freundlich isotherm as analyzed to determine adsorption isotherms for metal ion Pb(II), Zn(II) and Cd(II) at different pH values (4.00, 5.00 and 6.00) and different temperatures (25.0 oC, 35.0 oC and 45.0 oC) in the range of concentrations from 20.0 to 150.0mg/L. The adsorption isotherms results are presented in Table 3 and shown in Figure 8 & (Table 2) (20-23).

Figure 8: Plots of a) adsorption isotherm b) Linearized Freundlich c) Linearized Langmuir of Pb(II) at pH = 6 and 45 °C.

Table 3: R², qm, and KL values obtained from Langmuir plots

In the Langmuir model, the values of correlation regression coefficient (R2) are greater than 0.90 and had excellent linearity. This indicates that homogenous sites of interaction are better to describe the process and the maximum sorption capacities (qm) deduced from these results indicated that the polymers has the highest capacity towards Pb(II) ions, but it shows a lower capacity towards Cd(II). It is observed that the adsorption capacity (qm) increases as the temperature and pH values increase for all investigated metal ions. Comparing the values of qm of the synthesized polymer to literature values Table 2. Typical qm values obtained in this work at pH= 6.00 and 45.0 oC for the adsorption of various metal ions on our polymer were as follows:

Metal ion: Pb(II) > Zn(II) > Cd(II)

qm (mg/g) = 35.7 > 23.8 > 22.7

Metal ion: Zn(II) > Cd(II) > Pb(II)

qm (mmol/g) = 0.36 > 0.20 > 0.17 (Tables 3 & 4).

Table 4: R², KF and n values obtained from Freundlich plots

The trend in qm values in poly(1,4-cyclohexanedimethylen phthalate) at pH= 6.00 and 25.0 oC is Pb(II) > Cd(II), in (mg/g) were 53.5>17.7 respectively [15]. The trend in qm values for poly(1,4- cyclohexanedimethylene oxalate) at pH= 4.00 and 25.0 oC is Pb(II) > Cd(II) > Zn(II), in (mg/g) were 31.2 > 29.8 > 15.9, respectively [19]. The trend for Pb(II) and Cd(II) ions in poly(hydroquinone oxalate), and in poly(neopentyl oxalate) polymer, were as follows: Pb(II)>Cd(II) [24-27] and thus the results similar in order the metal ion with our results in the literature [23] that is qm values 207.7 >30.7 >19.1 for Pb(II) >Zn(II) >Cd(II) in poly(bisphenol A oxalate). The results indicate that our polymer has reasonable qm values. In the Freundlich model, both KF and nare Freundlich constants, being indicative of the adsorption capacity and the adsorption intensity respectively. High value of n between (1.4-3.6) indicates that adsorption is good over the entire range of concentration studied, while small values of n means that the adsorption is good at high concentrations but much less at lower concentrations and the values of n were greater than one indicating that the adsorption was favorable. A greater value of KF indicates a higher capacity for the adsorption than smaller values [28].

Dubinin-Radushkevich

The linear form for Dubinin-Radushkevich (D-R) isotherm has the following expression:

R is the ideal gas constant (8.3145 J.mol-1.K-1) and T is the

absolute temperature (Kelvin). The values of p and q max are evaluated from the slope and intercept of the linear plot of lnq versus s2, where q max is related to the adsorption capacity and p is the constant related with the adsorption energy. The free energy of adsorption (E) is defined as the free energy change required for transferring one mole of ions from solution to the solid surface, this energy is calculated as follows:

Table 5: Dubinnin-Radushkevich (D-R) isotherm parameters for Pb(II), Zn(II) and Cd(II).

As illustrated in Tables 3-5, the values of E for Pb (II) are (0.1100.600 kJ/mol), for Cd(II) are (0.080 -0.200 kJ/mol) and for Zn(II) are (0.180-0.310kJ/mol). All values are less than 8.00kJ/mol, this indicates that physical forces affect adsorption. The result of the concentration variation isotherms of polymer (Table 5) and the plots of Dubinin-Radushkevich at pH= 4, 5 and 6 at 25 °C, 35 °C, 45 °C are shown in Figure 9.

The Effect of Temperature on The Uptake

The effect of varying temperature on the % uptake of metal ions was also investigated. The results are obtained by plotting % uptake at different pH against temperature and are presented in Figure 10. The results obtained showed that the adsorption process of Pb(II) , Zn(II) and Cd(II) onto the surface of the polymer is an endothermic process since the % uptake increases as the temperature increases nearly at all tested pH values.

Figure 9: Plots of Dubinnin-Radushkevich (D-R) isotherm for the adsorption of Pb(II) on the polymer at pH= 6.00 and a) T= 25 °C, b) T= 35oC, c) T=45 °C

Arrhenius Parameter

Table 6: The Arrhenius parameters for Pb(II), Zn(II) and Cd(II) at pH=6 and temperatures 25.0oC, 35.0oC, 45.0oC.

Table 7: The Arrhenius parameters: Activation energy ( E) and pre-exponential factor (A) for Pb(II), Zn(II) and Cd(II) at pH=6 and temperatures 25oC, 35oC, 45oC.

Arrhenius equation can be used to determine the activation energy and pre-exponential factor for a reaction were calculated from Figures 11 and shown in Table 6. The results A and Ea values that obtained in Figure 11 and Table 6 are calculated from Arrhenius equation:

Ln k = - Ea / R T + Ln A .....(4) (Table 7)

Where k is the rate constant, Ea activation energy, R gas constant and A pre-exponential factor. The values of A and Ea can be calculated from intercept and slope of a straight line of a plot of Ln k against 1/ T. The pre-exponential factor A is the constant of proportionality between the concentration of the reactants and the rate at which they collide. The activation energy Ea is the minimum kinetic energy required for a collision to result in reaction, through the more favorable molecular orientations. The factor exp (-Ea / RT) represents the fraction of molecular collisions that have an energy value equal to or greater than the activation energy Ea. At higher temperatures a larger portion of reactant molecules will have the required Ea to react. Thus, the reaction rates depend on Ea, the reactant orientations (relative positions) during collisions and the temperature. Both A and Ea are approximately constant over a moderate range of temperature (50K) [29]. The order of Ea values for Pb, Zn and Cd is (19.2, 32.1, 83.9kJ/mol) respectively. This low value of Ea indicates a reaction rate slightly sensitive with temperature [30]. So, we cannot explain the mechanism of the process from activation energy only but needed to use Eyring equation [31].

The Eyring equation (activated complex theory)

Determination of activation energy, entropy and enthalpy of activation by this equation

Thus, the above general form ofthe Eyring equation or activated Complex Theory equation, also known as Eyring-Polanyi equation in chemical kinetics, relates the reaction rate to temperature and is trivially equivalent to the empirical Arrhenius equation. The results were calculated from Figures 11 & 12 and shown in Table 8.

Figure 10: The temperature dependence of % uptake of Pb(II) , Zn(II) and Cd(II) ions at pH=6.

Figure 11: The Arrhenius Plots of (a) Pb(II), (b) Zn(II) and (c) Cd(II) at pH= 6.00.

Figure 12: The Activated Complex theory Plots of (a) Pb(II), (b) Zn(II) and (c) Cd (II) at pH= 6.00 .

Table 8: Calculated thermodynamic parameters of activation (AH, ASt, AGt) at pH= 6 and 25oC.

The Eyring-Polanyi equation has been applied to rate processes and the calculation of values of enthalpies and entropies of activation without pointing out the significance of the obtained values and the difference between the activation energy values found by using the Arrhenius equation.

A plot of (Ln k/T) versus 1/T gives a straight line with a slope of -ΔHǂ/R from which the enthalpy of activation can be derived and with intercept of ln (kB/h) +ΔSǂ/R from which the entropy of activation is derived. From the values of the free energy of activation the real energy requirements are known, thus, suggesting the use of the Eyring-Polanyi equation mainly as a tool for gaining a deeper understanding of the actual processes at work and not only as a tool for predicting reaction rates based on measured rate constants. This relation is usually used for the suggestion of a mechanism for a certain reaction in the following way: the certain reaction is performed at various temperatures where the reaction rate constant is measured. The pre-exponential factor A of Arrhenius equation has been related to ΔSǂ of Eyring equation.

Low values of lnA correspond to negative values of ΔSǂ, the activated complex in the transition state has a more organized, more ordered and more rigid structure than the reactants. This happens when bonds are formed or substances are absorbed, and high values of lnA correspond to positive (or less negative) values of ΔSǂ, a positive value for the entropy of activation indicates that the transition state is disordered (less organized), compared to the state of the reactants. This happens when bonds are broken or substances are desorbed. The calculated value of the entropy of activation is used for the suggestion of a mechanism i.e. in replacement reactions: Associative (ΔSǂ< 0), Dissociative (ΔSǂ> 0), Interchange (ΔSǂ = 0). [32] In our results in Table 8, the values of ΔSǂ for Pb(II), Zn(II) and Cd(II) are -188.7, -164.7, -21.3 J/mol.K, respectively all the values of ΔSǂ< 0 indicated that the process has Associative mechanism. The relation between Ea of the Arrhenius and ΔHǂ of the Eyring equation (activated complex theory) is:

There was no comparison between Ea values and the ΔGǂ values that lead to the conclusion that Ea does not represent the full energetics of a process. Thus ΔGǂis the critical factor and not Ea. Thus, near room temperature (the thermodynamic temperature, 25 oC), Ea is roughly 2.5 kJ mol-1 larger than ΔHǂ. [32] Through Table (4.68) can be calculated divide between ΔHǂ and Ea for Pb(II), Zn(II) and Cd(II) that equal (2.6, 2.6, 2.5 kJ mol-1) respectively, there results indicated of the temperature independence on reaction rate and the temperature influences is room temperature 25 oC [32]. For, so, we needed calculate the free energies of activation ΔGǂ. It has been found that ΔGǂ gives a more realistic/true value of the "activation the processes need in order to take place and not Ea or ΔSǂ alone. The free energy of activation ΔGǂ includes not only the ΔHǂ component (= Ea-RT) but also the ΔSǂ component that may be important. The term -TΔSǂ that hΔSǂo be added to ΔHǂ in order to give ΔGǂ which may be critical,

ΔGǂ = ΔHǂ- T ΔSǂ......(8)

Determines the spontaneity of the reaction ΔGǂ

ΔGǂ greater than zero reaction is spontaneous

ΔGǂ0 = system at equilibrium, no net change occurs

ΔGǂ less than zero reaction is not spontaneous [33]. The results of ΔGǂ in Table 8 were explaining that all the values of ΔGǂ > 0. So, this process is spontaneous (physical process).

Distribution Coefficient (Kd)

The distribution coefficient is defined ΔSǂhe final concentration of metal ion in the sorbed form on polymer divided by its final concentration in solution. It is regarded a standard parameter in the assessment of the physicochemical behavior of metal ions between solid and liquid phases. It is calculated by the following equation.

Kd = qe / Ce = KL qm-KL qe........(9)

Table 9: Distribution coefficient for Pb(II) for different pH values and temperatures.

Where Kd is the distribution coefficient (L/g). Thus, a plot of (qe / Ce) against (qe) should be a straight line with slope= - K and an intercept= qm K if Langmuir equation is applicable The distribution coefficients (Kd) is calculated for the polymer at different pH values (4.0, 5.0, and 6.0) and temperatures (25°C, 35°C, and 45°C) are given in Table 9.

Thermodynamics of Adsorption on the Polymer

In order to understand the possible adsorption mechanism involved in the removal process, thermodynamic functions for the system, including changes in Gibbs free energy (ΔG°), change in enthalpy of adsorption (ΔHǂ) and changes in entropy of adsorption (ΔS°), were calculated using the following equation Using the following equation:

Where Kd is the equilibrium constant, R is the gas constant and T is the temperature in Kelvin.

The plot of lnKd against 1/T for each metal ion gives a linear relationship, where the values of enthalpy (ΔH^o) were entropy (ΔS^o) are obtained from the slope and intercept of lnKd vs. 1/T plots. AG^o was calculated at each temperature using the following equation:

Table 9 present the data of distribution coefficients at different temperatures and pH values, while Figures 13 show the plots of lnKd versus 1/T (Table 10).

Figure 13: Plots of ln KdVs 1/T for Pb(II),(a) pH =4.00 (b) pH=5.00 and (c) pH=6.00.

Table 10: Thermodynamic Functions for Pb(II) at T= 298.15 (K).

The results of the studies on the influence of temperature on metal ions adsorption are presented in Table 10 above. The positive values of enthalpy indicate that the adsorption removal increased with increase of the solution temperature. This shows that the adsorption process is an endothermic one. AG°, ΔHǂ, and ΔS° are the thermodynamic functions related to the experiment conditions. Spontaneity and favorability of the adsorption process is established by decrease in Gibbs free energy values, AG°. The value of AG° between (0.16 - 1.04) indicates the degree of favorability of the adsorption process, so the values of AG presented in Table 10 indicate that the adsorption of Pb(II), Zn(II) and Cd(II) is a favorable process [28]. All the values of AG° are very small and positive which suggests that the adsorption of metal ions onto polymer require some small amount of energy to convert reactants into products [34].

This is agreeing with values of Table 10 which represent to the degree of favorability of adsorption, the decrease of AG° values of Pb(II) >Zn(II) >Cd(II). As shown in Table 10 all AH values are positive this suggests the endothermic nature of metal adsorptions. One possible explanation of this is the well-known fact that heavy metal ions used are well solvated in water. In order for these ions to be adsorbed, they are denuded to some extent of the hydration sheath. This dehydration process of ions requires energy for removal of water from ions is essentially an endothermic process [35]. We assume that the energy of dehydration exceeds the exothermicity of the ions attaching to the surface [36]. The implicit assumption here is that after adsorption the environment of the metal ions is less aqueous than it was in the solution state.

The endothermic interactions between polymer surface and metal ions were accompanied by small positive values of entropy, which wΔS⫲he driving force for adsorption. The positive values of AS signify an increased state of randomness at the solid- solution interface following adsorption. Also the positive entropy of adsorption reflects the affinity of adsorbent for metal ions used. The adsorbed water molecules, which are displaced by the adsorbate species, gain more translational energy than is lost by the adsorbate ions, thus allowing the prevalence of randomness in the system [28]. The entropy changes were most likely to be due to structural changes and adjustments in the adsorbate as well the adsorbent. The structural changes arise from the release of ions like H+ from the polymer surface into the solution and also from partial solvation of the metal ions in water. The adsorptions of Pb(II), Cd(II) and Zn(II) on polymer were associated with entropy decrease in conformity with the general situation of ions existing in a more chaotic random distribution in aqueous solution compared to their adsorbed and immobilized states [37].

Column Experiments

Metal ion uptake by the polymer

The metal ion uptake by the polymer using column experiment for Pb(II), Zn(II) and Cd(II) was determined at pH 6.0 and 25.0 oC, initial concentration of 150.0 mg/L and a flow rate 1 mL/4min. The uptake for metal ions is represented in Table 11.

Table 11: Metal iron uptake using column experiments.

It can be seen that the uptake capacities of the polymer with the metal ions fall in the order;

This result is similar to the order of the metal ions in the batch experiment. However, the values of percent uptake for the metal ions in column experiment are lower than those obtained in batch experiments, because in order to achieve the complete saturation a much greater time is needed. On the other hand, there is no mechanical shaking associated with the column experiments, which result a decrease in percent of metal uptake.

Desorption Studies

Two eluting agents, 0.10 M HNO3 and 0.10 M EDTA were used for removal of metal ions, keeping the flow rate of elution 1 mL/4 min. The fluent was collected in five portions, 10.0mL for each portion; the results are expressed as percent recovery and represented in Table 12. The eluting agents react in two different ways: HNO3 act as proton-exchange agent and the second a complex-forming agent as EDTA. Depending on the values of the % accumulative recovery, in Table 12, the following trend was observed for the eluting agents of metal ions from the polymer:

0.1M HNO3 > 0.1M EDTA

Table 12: Desorption of Pb(II), Zn(II) and Cd(II) ions from the polymer.

The experiments confirmed that maximum metal desorption can be achieved with mineral acids in concentrations of 0.1M solutions. This could be attributed to cation exchange between the proton and metal sorbed. However, this method is more complex than protonation [8,38].

Conclusion

In this study, we prepared a polymer containing phthalate function group and capable of adsorbing the metal ion by solution polycondensation and characterization of poly(1,4- benzenedimethelene Phthalate). The structure and properties of polymer was confirmed by FT-IR, 1H NMR, 13C NMR, elemental analysis, SEM and thermal analysis. The sorption properties of the synthesized polymer toward Pb(II), Zn(II), and Cd(II) in aqueous solutions were examined under various experimental conditions using both batch and column experiments. The effective desorption for the metal ions was studied, and the coefficient of recovery of sorption ability was also investigated. The polymer has high sorption rate for Pb(II) observed during the first 24h with high percentage of uptakes toward Pb(II), Zn(II) and low percentage of uptakes toward Cd(II) ions. The influence of different pH on metals uptake showed that the metal-ion uptake by the polymer increased with increasing pH and reached a maximum at pH=6 for Pb(II), Zn(II), and Cd(II). The best conditions for adsorption of metal ions and maximum adsorption capacity (qm) on polymer surface are pH=6, T= 45°C and initial metal concentration of 150 ppm.

The obtained adsorption data showed fitting for Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherm models. The application of the Eyring equation to literature data i.e. the calculation of AH+, AS+ and AG+, has pointed out that in geochemical transformations it is necessary to calculate the entropy of activation along with the enthalpy of activation in order to fully characterize a process energetically. A column packed with the polymer has good metal uptake properties toward all metal ions, and followed the order: Pb(II) > Zn(II)> Cd(II) at pH 4.0 and 25 oC and flow rate 1 mL/4min. The efficiency of recovery of metal ions after adsorption can be carried out by treatment of the loaded polymer with 0.1M HNO3 and 0.1M EDTA with good percent recovery.

Acknowledgements

The authors would like to thank the Deanship of Academic Research and Quality Control (DAR) of The University of Jordan for supporting this work and all supervisors who worked in the improvement of this work.

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Lupine Publishers | Focusing on Food Security or Targeting the Economy: A Study on Maize and Cotton Production in Kandi Commune

 Lupine Publishers | Journal of Environmental & Soil Sciences 

Abstract

Maize and cotton are two crops that are highly produced in North Benin. Their production has advantages as well as constraints. These advantages and constraints are taken into account in the choice of the producer to cultivate one of them. The objective of this study is to present, at first, the advantages and constraints that the producers of Kandi commune face on these two crops. It also aims to expose the producers’ preference according to the advantages and constraints listed by them. To achieve this, the data were collected in two districts of the municipality over a period of two weeks. Semi-structured interviews were conducted with fifty producers through an interview guide. Data processing was carried out using a dual approach (quantitative and qualitative) which, on the one hand, consisted in carrying out statistical tests and, on the other hand, analyzing the statements collected during the data collection. The main statistical test used in this study is Kendall’s W-concordance test, which has been used to prioritize constraints. At the end of the analyses, it appears that cotton, just like corn, enables producers to meet the needs and social development of their households. On the other hand, the non-organization of the maize sector, the lack of inputs and the delay in their distribution, maize prices fluctuation and difficulties in the evacuation of cotton are the main constraints reported by producers. Despite its lack of organization and the other constraints to which it is subject, maize crop is the most preferred. In view of this, it would be appropriate to consider the organization of the maize sector and the optimization of the services provided by the organizations in charge of the cotton sector. This will be beneficial to both production systems and also to all actors involved.

Keywords: Food security; Income; Advantages; Constraints; Farmer’s choice

Introduction

Agriculture is one of the crucial activities that human being cannot neglect for his survival. It keeps the human species alive and contributes to its evolution. In Benin, it plays a great role in strengthening the economy and provide about 75% of jobs [1]. Among all the crops produced in the territory, two prove to be vital both in the constitution of the national economy and in the fight for food security: Those are corn and cotton. Known as the main cash crop in Benin [2] and the engine of the Beninese economy [3], cotton alone counts for 27% of exports and contributes by 7% to the national GDP. Its production has not stopped growing over the last five years. It reached in 2016, a tonnage of 451,000, which is an increase of more than 70% from the year 2015 [4]. Due to its multiple outlets, the cotton sector remains the country’s best organized sector [5]. If cotton receives a lot of attention from the Beninese government, corn itself does not have such a privilege. Nevertheless, it is the crop that could be an alternative to cotton production [6] in northern Benin. It comes second, after cotton as a subsistence and cash crop [7]. Indeed, its cultivation occupies nearly 70% of the total area devoted to cereals in Benin and represents about 75% of cereal production [8]. Together with cowpea, cassava and yam, it forms the staple crops of people’s diet [9]. Studies have shown that 63.1% of households in Benin consume 7 days out of 7, maize being the main cereal in the food ration [9]; [10]. Apart from the aspects raised, corn also has medicinal properties. According to [11], the corncob is used in combination with other plants to cure knee and low back pain. Some use it to treat diseases such as malaria.

Material and Methods

Study Area

The study took place in the municipality of Kandi, county town of the department of Alibori. Located in the agro ecological zone of the cotton pan, it is limited by the communes of Malanville (North), Gogounou (South) Ségbana (East) and Banikoara (West). It is spread out an area of 3421Km² and includes ten districts, sixty-seven villages and fifteen districts. The climate in Kandi is of Sudanese type characterized by two seasons that follow each other: The first, rainy from May to October and the second, dry from November to April. Climate change in sub Saharan Africa does not leave the Kandi commune on the side-lines. It is worth noting since a few decades in the commune and its surroundings an early drying up and a late or sometimes violent arrival of rains. Several studies carried out in the region have noted this [12-15]. In addition, the soil found at Kandi is of tropical ferruginous type. The relief is made up of plateau and one distinguishes by place hills made of granites and quartzite. As for vegetation, the town has grassy savanna, shrub and trees with some gallery forests. In terms of agricultural production, Kandi has a good reputation coming in second place after Banikoara, the giant cotton supplier in Benin. Apart from this asset, the municipality is essential in the department in terms of corn production. The following table gives an idea of the evolution of these two crops from 2011 to 2016 (Table 1).

Table 1: Production in tons of the last five years.

Analysis of this table shows a peak of cotton and maize production between 2014 and 2016 with a respective tonnage of 48853.09 and 102240. The respective average production of the two crops is 362681.86 and 66394.68 tons.

Methodological Approach

Among the ten districts of Kandi commune, only two were chosen to shelter the study. These are the districts of Angaradébou and Sonsoro. This choice was made in a participatory way with the coordinator of the Interprofessional Association of Cotton Producers. Firstly because of their performance in the production of both crops within the municipality and secondly because of their positioning. This choice was made for a wide variation of collected data and the obtaining of a socio cultural diversity in order to better touch the realities of the producers of Kandi as a whole. The data was collected using an interview guide designed to collect qualitative and quantitative data. The collection took place during the month of April of the year two thousand and eighteen (2018) and lasted 2 weeks. After an individual interview with five producers, the questionnaire underwent a slight adjustment. Faced with the unavailability of some farm managers, other people who were relatively close to them and involved in the farming activities of the households proved to be able to provide the necessary information for the study. A total of 25 subjects per district producing maize and cotton were included in the study. These have been identified by secretaries of cooperatives who hold leadership positions within their community. The following Table 2 provides an overview of the structure of the sample considered in the study.

Table 2: Structure of the study sample.

Data Analysis

The data capture and analysis was carried out exclusively with SPSS v21.0 32bits software. The data processing was done using descriptive statistics, speech analysis and Kendall’s W-concordance test. The descriptive statistics essentially allow to obtain the frequencies and average of variables characterizing from a social and demographic point of view the interviewed farmers. The comments received from producers were analyzed and then used to model the “benefits and constraints” section. This technique was chosen inspired by the work of several authors including [16- 18]. The Kendall’s W-concordance test was also used to prioritize production constraints in order of importance.

Results

Table 3 below summarizes the socio-demographic characteristics of the producers surveyed in this study. It indicates that the subjects included in the sample are predominantly male (90%) with a low representation of women (10%). Ninety-four per cent of them live entirely depending on agriculture, compared to six per cent who make it as a secondary activity. Their farming experience varies from 3 to 40 years with an average of 16.92 years. Compared to the size of farm households in both localities (13 persons), the average number of farm active Worker (7 approximately) is relatively small. Farmers send their children to school until they are unable to move on. Sixty percent received formal education and forty percent got literate in local languages. Among those who have been literate 22% hold the certificate of primary school, 10% hold the certificate of secondary school and 2% hold the high school diploma and bachelor’s degree. Anyone wishing to cultivate cotton is required to belong to a Village Cooperative of Cotton Producers, this justifies the membership to an organization unanimously own by the respondents. The average area of cotton planted is 6.62 ha on an average total area of 15.62 ha. In contrast, the average area of maize grown is 5.69 ha. An observation of these figures allow to say that the cotton takes with a small difference, the top on the corn in terms of cultivated area in the commune. This could be explained by the several constraints faced by corn producers. Note that these results are quite similar to those obtained by [19] in their studies in the same commune. able 2: Structure of the study sample ese two crops from 2011 to 2016.

Table 3: Socio-demographic characteristics.

Advantages

Advantages Related to Cotton Production

Cotton plays a major role in the lives of Kandi producers. From the exchanges held with the 50 people surveyed, it appears that several benefits are derived from the production of cotton. It allows heads of households and farms to make investments (buying cattle for traction, rolling stock, building houses ...), to perform ceremonies (marriage, baptism, burial ...) and then to meet regular expenses in their households and farms (schooling, food, expenses and debts of agricultural campaigns). The Interprofessional Cotton Association known as ‘’AIC’’ is the structure in charge of the cotton sector throughout the national territory. It has set in place a mechanism that allows producers to get inputs on credit before the campaign. They receive the inputs on credit, use them for production, and subsequently pay their debts at the time of payment. This approach is appreciated by the producers because, they lack sufficient financial means at the time of starting the campaign. Through the comments transcribed below, two producers support what has been said above. “The cash of cotton appears for me like a tontine, it allowed me to buy my bike, to build the house where I live. Thanks to the cotton I bought a ginning machine that serves me a lot after the corn harvest. My eldest son is already old enough to marriage. I need to buy him a motorcycle and prepare for his wedding by next year. It is on the cash of the cotton that I count to be able to do it. “ “The cash we get from cotton also allows us to do ceremonies. It is an obligation for us. In our culture, when someone close to your family dies, that means that your money is dying too. You cannot have money hidden somewhere without doing it. It’s like a duty for us.

Advantages Related to Maize Production

Corn in the first place ensures the food needs of households and the farm. After production, much of the crop is set aside to allow the producer, his family and those who serve him to overcome hunger, one of Maslow’s primary human needs. In the same way, the seeds used by the producers are taken from the previous crops. Apart from these two aspects, a great part of the producers have said that corn helps them financially. In fact, after harvest they reserve a larger portion for commercial purposes. The main reason behind this, is to cover regular expenses and household contingencies. These unforeseen events are usually cases of illness or death. Growing maize for the farmer is therefore a way to keep his relatives in safe from the food and financial point of view. The comments collected on this issue were analyzed and reissued below. “Corn helps us a lot, that’s what we eat at home almost all the time. In the form of dough, boiled, and akassa (local meal made with corn). When we are facing a financial problem we just have to take a bag of maize, sell it and the problem is solved. “Cotton’s cash lasts before coming. All the while, it’s corn that keeps us alive. Corn helps us a lot without lying to you.”

Cotton Production Constraints

The benefits of cotton and corn production are enormous. However, during the survey, producers listed a number of constraints they face every day. Seven main constraints came back during the exchanges. They have been grouped in the following table with their respective average ranks. It is noted after analysis of the table that the main constraint reported by the population studied is the insufficiency of the seeds supplied to them. The majority of producers have not only deplored the lack of seeds but also the late availability of these inputs. Similarly, the removal of seed cotton, the late payment of cotton costs, the inadequacy of herbicides and the high cost of inputs are the secondary constraints recorded in this study. It is also important to note through the Kendall coefficient (0.379) that the order of importance of these constraints varies quite remarkably from one producer to another (Table 4).

Table 4: Classification of constraints related to cotton production.

Corn Production Constraints

Concerning corn production constraints, there is a relatively high degree of agreement on the ranking (Kendall’s coefficient = 0.698). The first three constraints recorded are the lack of specific inputs for maize, the obligation to sell cheap the crops, and the lack of financial means to cover the expenses inherent to production. The lack of agricultural equipment and the fluctuation of the price of maize occupy the last places in this ranking (Table 5).

Table 5: Classification of constraints related to corn production.

Corn or Cotton

The objective of this section is to expose the respondents’ position after having simulated a situation where they are faced with making a choice between the two crops. It also aims to explain the reasons justifying their respective positions. Table 6 presents the distribution of producers according to the crop chosen. From this table, it appears that more than half of the producers (58%) chose corn, 22% cotton and 20% decided not to take a position. Table 7 below is a summary of the reasons given by the producers following the choice made. Producers, who opted for cotton justify their choice by the fact that the sector is organized, the price is fairly stable, and inputs are provided on credit. At the same time, those who chose maize justify this by its ability to cope with the producer’s financial problems, its ability to keep them alive before the arrival of cotton revenue and also by its easiness and short production cycle. Producers who have maintained a neutral stance argue that the two crops are inseparable and that in the current context, corn production is necessary in order to reap the benefits of cotton.

Table 6: Crop chosen by farmers.

Table 7: Summary of the reasons given by the producers following the choice made Farmer stances.

Discussion

As maize is a foodstuff, it is mainly used to cover the food needs of producers and their households. The forms under which it is consumed differ from one region to another, or even from one social category to another [20]. In Kandi commune, it is consumed in the form of porridge, paste and akassa. Secondarily, it is the subject of a commercial transaction and generates significant income for producers. After discussions with these producers, it is noted that the income earned is used for security purposes and social fulfilment. Purchases of food, buildings and ceremonies (marriage, baptism, death ...) are the main uses made of these incomes. They also, but very rarely, invest money that can add value to their production. Purchasing production equipment is generally limited to the minor tools that are necessary. This could be explained not only by the relatively large size of households living at the expense of these incomes, but also by the primacy of physiological and security needs over other needs. The difficulties that undermine the maize sector in the municipality are enormous, as well as the benefits that result from it. The lack of specific maize inputs outweighs all constraints by unlawfully resorting to inputs for cotton production. According to [5]; [7] and [21], this diversion is reflected in the low yields obtained at the cotton level. One could say that maize seems to be in the study area a parasite of the cotton crop. Studies conducted by [22] on the corn seed production and distribution system in accordance with this study revealed that the lack of input is one of the main weaknesses of the maize sector. The study also shows that, apart from the lack of inputs, the sale at low prices of harvests is a strategy developed by producers in urgent need of financial means. They are often lacking when they harvest the cotton. Cases of illness or other unforeseen events arise occasionally. In response to these problems, they sell corn crops. Those who do not adhere to this practice generally resort to Micro Finance Institutions (MFIs) loans as mentioned by [23]. The ‘‘warrantage’’, (a sort of securing by storing a part or the full harvest) implemented in Benin for more than a decade [24] in response to this situation hasn’t unfortunately had a significant impact in the study area. With regard to cotton, it is noted that income from production has the same purpose as corn, with the difference that cotton is exclusively sold and used more for sustainable projects. In some localities in the study area, cotton producers pay contributions after receiving cotton income to build classrooms or other community infrastructures. Numerous producers greet the organization around the cotton sector and mainly the credit-input which is granted to them. This credit would allow them, according to [25], to effectively fight against pests and raise the level of fertility of their land. Nevertheless, the high cost of inputs, the insufficiency of seeds supplied and especially the delay in their delivery are denounced as the real handicaps of the sector. Many are forced to informally leave money in order to have the extra amount of seed needed. Added to this, the evacuation of cotton harvests from the production areas to the factory loses its nature of gratuity at a given period of the campaign. All these constraints call into question the performance of the production system.

Conclusion

The aim of this study was to shed light on the two most important agricultural value chains in northern Benin. This, through the advantages and constraints that characterize their productions. At the end of the study, it appears that cotton as much as maize represents a lot. farmers. Corn is the staple of their diet and significant revenues are derived from the production of both crops. These revenues are mainly used to meet the needs of households and their social development. Cotton, on the other hand, enables producers to meet their economic and social needs. Besides, the two production systems are subject to constraints that need to be considered for the betterment of these sectors and the actors involved. Giving common attention to both crops through the organization of the maize sector and the optimization of the services provided by the AIC are means likely to boost the satisfaction of all the actors involved.

Acknowledgments

The authors of this paper express gratitude to all those who contributed to the success of this study. They especially thank Mr. Soufianou ARZOUMA, Mr. Washiou ATCHAOU and Mrs. SANNI Adéline for the introduction in the investigation zones and the preparation in local language. A kind regard is also addressed to Mr. Lafia Baky and Mrs. Gauthe Faïdath.

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