Synthesis and characterization of modified Poly(Ethylene-Co-Vinyl Alcohol) and its application as a biocidal agent

ABSTRACT


Introduction
The microbiological contamination of water causes various negative effects on the human health, because of the spread of infections, and the quality control difficulties of the microbial corrosion and fouling, caused by the biofilm layer [1].The conventional methods for water treatment concludes different mechanical and physical process [2,3].Furthermore, the chemical treatments have been applied, such as the application of different chemical agents (disinfectants, biocides) to inactivate microorganisms [4,5] .Chlorination is the most applied treatment that involves some difficulties, as the evaluation of toxic byproducts [6].The infection by pathogenic microorganisms has a Delta Journal of Science Available online at https://djs.journals.ekb.eg/DJS Vol.42 (1) (2020) pp.15-20 .great potential in various applications, particularly in the medical fields, health care, and hygienic applications, textiles, water treatment, dental surgery and food industries [7], [5].Antimicrobial agents are defined as materials that are able to kill pathogenic microorganisms [8].The application of antimicrobial copolymers decreases the environmental impact related to the conventional antimicrobial agents by the reduction of their residual toxicity, and hence optimization of their efficacy through controlling their lifetime.Moreover, the antimicrobial polymers are nonvolatile chemically stable agents that cannot invade through the skin.In this area, infections related to the biomaterials, signify a certain task to the medical implants [9][10][11].Efficient copolymers is referred to both the functional groups and to their polymeric nature that their features be influenced by the extraordinarily size of the polymeric molecules [12-14].Antimicrobial mediators are applied for various applications, for instance water disinfection, medications, sterilization, and the inhibition of the microbial growth[13], [15][16][17].Ethylene vinyl alcohol copolymer (EVOH) is a semi-crystalline copolymer of ethylene and vinyl alcohol monomeric subunits.P(EVOH) is a well-known flexible thermoplastic copolymer for packaging, funnel tanks, and different medical techniques [18].The synthesis of EVOH has been adjusted depending on their applications, for example, films, nanoparticles, and nanofibers [19,20].Several reasons for the selection of EVOH in this research.First, the polymeric material is highly hydrophilic because of the vinyl alcohol subunits.Second, it is a waterinsoluble referred to the ethylene subunits.Third, the good biocompatibility of EVOH; and finally, the other hydroxyl functionality exhibits chances for chemical modification [2,21,22

Test microorganisms and media
The tested microorganisms were Escherichiacoli, Streptococcusaureus, Klepsiellasp and Proteus sp in addition to some fungi such as Asperigillusniger and pathogenic Candida spp.(C.krusei, C. albican, C. tropicalis and C. glabrata).The tested microorganism was obtained from the Bacteriology and Mycology unit, Botany Department, Faculty of Science, Tanta University.

Chloroactylation of poly (ethylene co vinyl alcohol)
Pyridine (55 mL ) was added to a suspension of EVOH (27 % , 32 % , 38 % and 44% ) (10 g ) in 100 mL DMSO and the mixture was cooled to 0 C. Chloroacetylchloride (55 mL ) was added dropwise and stirred at 0 C for 3 h and room temperature for further 4 days .The insoluble part was removed by filtration and the filtrate was collected and concentrated on the rotary evaporator.The product was precipitated by adding distilled water, filtered off washed with water and was dried under vacuum at 40 C for two days.
Copolymer (1) 25 °C.After one hour, 10 ml of water in the glass beaker were withdrawn to measure the amount of urea released from the matrix and the same volume of fresh water was were the same as that of loaded CRUF) were also carried out, respectively.The study of the release of urea from superabsorbent composite was carried out as described in the experimental part.The best

Study of urea release from the CRUF matrix in water
The release behavior of urea from the CRUF in distilled water was studied according to the following procedure: 0.3 g of the CRUF was contained in a tea bag-like tissue and then immersed in 200 ml of distilled water in a glass beaker properly covered and kept at replenished.Detection of released urea was performed using UV-Vis spectrophotometer.According to Ehrlich reaction, P-N,N' dimethylamino benzaldehyde reacts with urea to give a lemon Kelly color which would absorb visible light at 440 nm.All the release experiments were done in a triplicate, and their results were averaged.

Release of urea from CRUF in soil
In order to demonstrate the release of urea from superabsorbent composite in agricultural field, release experiments in soil column were done.The soil used in this experiment was airdried and sieved to less than 2 mm.Polyvinyl chloride (PVC) pipe of 45 mm internal diameter was used to hold soil.Loaded CRUF (2 g) was well mixed with 200 g dry sandy soil and placed in the PVC pipe.The bottom of the tube was sealed by nylon fabric.Water was added slowly by a perfusion tube (one drop every 10 s).The time started when water seeped from the bottom of the pipe, i.e. water saturation.The leached water was collected, from which urea was estimated by the ultraviolet spectrophotometer [7].Control experiments, i.e. urea, (the amounts of urea

Amination of chloroacetylated poly(ethylene-co-vinyl alcohol) Amination with Ethylene diamine
A suspension of copolymer (1) (3 g) is added to 30 mL of ethylene diamine.The reaction mixture was stirred at 90 C for 7 h, then remain the reaction mixture to complete for 24 h.The product was filtered off, washed with distilled water then with ethanol to remove the excess of ethylene diamine.The product was dried at composite-urea formulation that can give good controlled release behavior was selected.
To investigate the properties of the selected composite as a new controlled release system, various formulations were prepared from the selected composite and urea as shown in table (1).The release measurements were carried out in distilled water at room temperature (25 °C) and the release was monitored using UV spectrophotometer at 440 nm.
The studies were carried out for 16 hours the results showed clearly that on increasing the amount of composite in the formulation from 10 wt% to 50 wt%, the release rate decrease and release time increased from 3 hours (in case of CRUF1) to 16 hours (in case of CRUF5).
Figure (1) depicts the release profiles of urea from loaded controlled release urea fertilizer (CRUF) with different urea loading percentage in distilled water (swollen in aqueous solutions of urea with different concentrations).Even though pure urea dissolve in water entirely in five seconds, CRUF1 released 100% of its urea after 3 hours while the CRUF2 released 100% 0f urea after 6 hours.Similar results were obtained for CRUF3, CRUF4 and CRUF5 which released 100% of urea in 10, 13 and 16 hours, respectively.
It was found that during the first hour of release study, the CRUF1 released 35% of urea, while CRUF2 released 12.5% of its urea content.The decrease of percentage of the released urea was repeated with the other formulations.The first hour release of CRUF3, CRUF4 and CRUF5 were 10.8%, 7% and 6.5% respectively.The high percent of the released urea from CRUF1 could be due to the release of urea adsorbed on the composite surface and pores formed on the surface CRUF.
The formed pores on the surface may have led to easy penetration of water vapor to the urea entrapped in the core causing the initial release of urea in the first hour of release study as the coating composite has not reached the swelling equilibrium yet.After the swelling equilibrium is reached, all the pores on the surface may have been closed forcing urea release from the CRUF to follow a diffusion mechanism from the interlayers of the composite.
The decrease in the rate of the released ureacomposite formulation was noted by increasing the superabsorbent composite content.This could be attributed to the fact that the release is diffusion controlled.Therefore, on increasing the percent of superabsorbent composite, more barriers are formed which decreases the diffusion rate and consequently the release rate of urea.After the swelling equilibrium was achieved, the perfect swollen samples were formed.as shown also in Figure (3), the urea released 44.5%, 68.4% and 99.5% within 1, 5 and 10 days, respectively.The urea release characters of loaded CRUF in soil was similar to that in water except that the release rate was slower in soil.It is well known that urea is easily dissolved in water, so it would quickly dissolve in the soil solution, and then release out of the soil by purge water, therefore, the release rate of untreated urea was very fast.However, for the loaded CRUF, the release of urea could be described by the following steps: 1) CRUF was slowly swollen by the water in soil and then transformed to hydrogel, and urea dissolved.
2) Urea could be released or desorbed slowly through the dynamic exchange of free water between soil solution and CRUF [9].3) The released urea was purged out of the soil by water.The reasons for the slower release rate in soil than in water may be due to the existing of many kinds of ions in soil solution, the swelling degree of CRUF is less in soil than that in distilled water, then the diffusion of urea in it would be difficult [10].Moreover, when the urea passed through the soil column, there are many-time absorbing and deabsorbing processes between urea molecule and soil granules, which also contribute to the slower urea release rate in soil.The effect of pH on the release of urea from the controlled release fertilizer (CRUF5) To investigate the effect of the pH of the release media (aqueous media) on the release rate of urea, the release was conducted in the different pHs media (pH4, 7 and 10).Figure (2) shows that there was a slight difference in the release behavior of urea from the CRUF5 in the various pHs that 100% released after 11, 16 and 14 h for pHs 4, 10 and 7 respectively.This could be attributed to the presence of different ions.The presence of cations like Na + , Ca +2 , Mg +2 , Fe +3 , H + and others lowered the swelling of the composite involved in CRUF5 formulation due to the screening effect of these cations on the anionic hydrophilic groups, which restricts the expanding of polymeric network and consequently increase the release rate of urea from the urea-composite formulation.

Fig. (2):
The release rate of urea from CRUF5 in different media.

Release of urea from CRUF in soil
Because there are many factors that could affect the release of urea from loaded CRUF in soil, such as the kind of soil, cation exchange capacity (CEC), water content, bulk density, urea concentration, gel collapse and so on, there must exist obvious differences for urea release from loaded CRUF between in distilled water and in soil.Therefore, we measured the urea release behaviors in soil.Figure (3) shows the urea release behaviors of loaded CRUF and untreated urea in soil.The urea release rate of untreated urea was very fast (as shown in figure (3).While the urea release rate of loaded CRUF decreased obviously compared with that of urea, the result was in agreement with that of Smith [8],

Conclusion
The release study of urea from the formulated controlled release urea fertilizer (CRUF) showed that the rate of urea release from the formulated CRUF decreased with the increased composite content while pH had no evident effect on the release rate.The prepared CRUF showed that urea could last in soil for nearly 12 days while pure urea disappeared from soil after about 3 days only.

Table (
1): Feed composition of the different prepared CRUF samples.