Studies and Development of Interpenetrating  Polymer Networks from Linseed oil and Corn oil

 

K. Priya Rajini¹* and S. Begila David²

¹Department of chemistry,  Sun College of Engineering and Technology, Nagercoil, Kanyakumari District, Tamil Nadu, India.

²Department of Chemistry Scott Christian College, Nagercoil, Kanyakumari District, Tamilnadu, India.

*Corresponding Author E-mail: kpriyasingh13@gmail.com.

Plantoils such as linseed oil and corn oil have been used for the preparation of Interpenetrating polymer networks for special applications. Epoxidation of linseedoil (ELO) and corn oil (ECO) had been carried out by per acetic acid method. Further an Acrylated epoxy resin of Linseed oil (AELO) and Corn oil (AECO) were synthesised from (ELO) and (ECO) .The (AELO) and (AECO) were characterised by physicochemical properties. The IPNs of  biopolymers were prepared by using comonomers like Vinylacetate (VA) , Vinyl pyrrolidone (VP), Methyl meth acrylate(MMA) and Methyl acrylate (MA).These biopolymers were characterised by tensile strength, crosslinked density,FT-IR spectral analysis and Biodegradability. The outcome of the studies revealed that the newly prepared IPNs of polymers are potential biodegradable material for various consumer applications like package materials, sporting goods and floor mats.

 

 

 

INTRODUCTION:

Since petroleum resources are ultimately limited, polymers based on vegetable oils are of great interest because they are renewable and could significantly contribute to a more sustainable development^{1, 2}.Vegetable oils such as linseed and tung oils are drying 0ils, which can self-crosslink under atmospheric oxygen, have long been used in the coating industry³. Semi-drying oils like soybean oils are of plentiful supply and therefore of relatively low cost, have also attracted great interest for the preparation of polymers or resins⁴. In recent years, with the rising cost of fossil raw materials and environmental issues, polymers derived from soybean oil have demonstrated strong cost performance competitiveness in many market applications⁵. However, the ability to obtain structures of sufficient mechanical or thermal properties has remained a challenge. In the recent decades an ever growing demand for improved polymer properties has paved the development of the blending of polymer mixtures^6,7.

 

In order to overcome the poor biological performance and to improve mechanical strength a new class of polymers has been introduced which are based on blending of either natural or synthetic polymers alone or in combinations. An interpenetrating polymer network (IPNs) is defined as a blend of two or more polymers in a network with at least one of the systems synthesized in the presence of another⁸.This results in a formation of physically cross-linked network when polymer chains of the second system are entangled with or penetrate the network formed by the first polymer. Each individual network retains its individual properties so synergistic improvements in properties like strength or toughness can be seen⁹. An IPN can be distinguished from polymer blend in the way that an IPNs swells but does not dissolve in solvents and creep and flow are suppressed¹⁰.They are also different from graft copolymers and polymer complex that involve either chemical bonds and or low degree of cross-linking. From this point of view only, IPNs can be generally named “polymer alloys” through which polymer blends can be made chemically compatible to achieve the desired phase morphology ¹¹. IPNs can be distinguished from the other multiple systems through their bi continuous structure ideally formed by cross-linking of two polymers   that are in intimate contact but without any chemical contact and yields a material with improved properties depending on the composition and degree of cross-linking .The concept of IPNs goes back at least as far as 1914 when the first interpenetrating polymer network was invented by Aylsworth¹².This was a mixture of natural rubber, sulphur, and partly reacted phenol-formaldehyde resins. The term IPNs was introduced for the first time by Miller in 1960s in a scientific study about polystyrene networks¹³. The present study explores the potential utility of interpenetrating networks such as Linseed oil and corn oil for the preparation of Novel cross linked bio polyesters eco-friendly biodegradable materials for various consumer applications like packaging materials and sporting goods.

 

EXPERIMENTAL AND METHODS:

Linseed oil and corn oil were purchased from the supermarket, acetic acid (glacial),hydrogen peroxide (Rankhem), Vinyl acetate (sigma Aldrich),Vinyl pyrrolidone (Sigma Aldrich), Benzoyl peroxide (Merk), Triethyl aniline (Merk) were purchased from respective dealers. All the materials were used without purification. Epoxidation of oil using 30% hydrogen peroxide was carried out by per acetic acid method¹⁴. Epoxidation of linseed oil (ELO) and corn oil (ELO) were carried out by using sulphuric acid, glacial aceticacid and hydrogen peroxide. Then (ELO) and (ECO) acrylated  using acrylic acid, triethyl amine  and benzene. Acrylated epoxidized linseed oil (AELO) and Corn oil (AECO) were mixed with 1:1 ratio and cross linked using co monomers like Vinyl acetate(VA), Vinyl pyrrolidone (VP), Methyl acrylate (MA) ,and Methyl meth acrylate (MMA),Benzoyl peroxide as free radical initiator and N,N diethyl aniline as accelerator. The mixture was casted on a clean silicon oil spreaded glass plate cured for 1hour at 100⁰c. All the cured materials showed high toughness, elastomeric and good transparency.

 

Characterization of biopolyesters

The AELO and AECO resin were subjected to extensive analysis for the determination of specific gravity, iodine value, saponification value as per the ISI standard 1964.The molecular weight was determined by GPC using µ Styragel column, 100 A⁰, UV detector and 280 nm filter.  FT-IR spectral analysis of the four biopolymers was done by magna-IR 550 spectrophotometer. The tensile strength of the biopolymers were determined using rectangular shaped polymer samples in the form of strips Test speed: 10mm/min; Tested with 100N load cell; Instrument used: instron model 3345. The values represented are an average mean of about 5-6 samples. The cross link density or effective numbers of moles of cross linked units per gram of polymers were determined using the modified Flory Rehner equation.

 

Biodegradation tests

Soil Burial Test

The soil burial degradation test of polymer was carried as per ISO 846:1997.The replicate pieces of the poly triglyceride esters (5 cm x 3 cm) were buried in the garden soil at the depth of 30 cm from the ground surface for 3 months, innoculated with the sewage sludge having ability to adhere and degrade the polymer film. The test specimen was periodically removed from the soil and the specimen was then gently washed to remove attached soil and dust after being dried in vacuum oven. The extent of degradation was examined by weight loss and surface observation. Scanning Electron Microscope (SEM) was used for assessing surface damages of polymeric sheet subjected to soil burial test.

 

Microbial studies

Bacterial adhesion and antimicrobial activity were evaluated by agar diffusion method. For bacterial adhesion study samples of 1 cm square pieces were used and for antimicrobial activity spherical disc of 10 mm diameter were used. Both test samples were sterilized by autoclaving before performing the test and finished by agar diffusion method. The test was done in triplicates. Gentamycin (10 μ / disc) of positive control was used for antimicrobial activity testing. The microbial strains used for bacterial adhesion study were Escherichia coli ATCC 25922 and S.aureus ATCC 25923.

 

RESULTS AND DISCUSSION:

Linseed oil and corn oil is a mixed glyceride of unsaturated components (lionleic acid,oleic acid) and saturated component (palmitic and stearic acid), since the concentration of unsaturated compounds are higher the mixed unsaturated triglyceride molecule offers a number of reactive sites, C=C bonds, the carbon alpha to the ester group for functionalisation^15,16.Under present experimental conditions epoxidation takes place at the double bonds of the triglyceride units. Reaction of the epoxy-functionalized triglyceride with acrylic acid incorporates acrylates in to the triglyceride^17. The reaction of epoxidized oil with triethyl amine catalyst by acrylic acid leads to the formation of Acrylated epoxidized linseed oil (AELO) and Acrylated epoxidized corn oil (AECO), The analytical data are given in Table1.

 

 

Table 1. Physical properties of AELO and AECO

Parameters	Acrylated epoxidised linseedoil (AELO)	Acrylated epoxidised corn oil (AECO)
Specific gravity gm/ cc at 300c Saponification value Iodine value   Molecular weight/calculated Hydroxyl Number   Molecular weight/ Saponification Value Molecular weight (GPC)	0.693   79.7 49.6   1467   0.623   2017     2108	0.722   86.6 53.72   1938   0.723   1939.9     2014

 

Iodine value represents the degree of unsaturation (=bonds) in the triglyceride oil. The iodine value is increased significantly in the AELO and AECO resin due to the unsaturated acrylate side chain in the resins. Saponification is applied to the hydrolysis of fatty acid ester under alkaline condition. Saponification number is used for the determination of the size, average molecular weight of the fatty acid and to estimate the non fatty impurity if present. Therefore the molecular weight of the compounds were determined from the relation molecular weight= 168,000/saponification value. The molecular weight determined by this method match the calculated value. The hydroxyl value determined the number of hydroxyl groups.

 

Molecular weight between cross links crosslink density

Molecular weights of linear polymers may be determined by appropriate physical measurements on very dilute solutions. Most commonly practiced methods are gel permeation chromatography (GPC) and intrinsic viscosity. Light scattering, ultracentrifugation and osmometry are also used in the determination of molecular weight of polymers. However, all of these methods require the solubility of the polymer, and therefore cannot be used to determine the molecular weight of an insoluble, cross linked polymer. Crosslink density plays an important role in determining the properties of polymers. The cross linked polymers only swell and do not dissolve in a non reactive solvent. The degree of swelling in a non reactive solvent determines the degree of cross linking and the molecular weight between cross links. The cross density of the polymers was determined according to ASTM D 792. The cross link density, of the polymers was determined from the solubility parameter of the polymer. The solubility parameter of the polymers was determined by conducting swelling experiments using small rectangular specimens in nine different solvents . Among all solvents used, dimethyl acetamide (DMA) gave the maximum swelling; hence its solubility parameter was taken as being equal to the solubility parameter of polymers. The polymer solvent interaction parameter χ is given by

 

Where, Vs is the molar volume of the solvent, R is the gas constant, T is the absolute temperature, δ_S are the solubility parameter of DMA, and δ_P is the solubility parameter of polymer. If δ_S = δ_P , the polymer solvent interaction parameter becomes equal to the lattice constant. The crosslink density or effective number of moles of cross linked units per gram of polyester was determined using the modified Flory Rehner equation

 

 =

 

Where,

 =  Volume fraction of the polymer in the swollen state,

 =   ( 1 / 1 +Q )Where, Q is swelling coefficient

    dr  = Density of polymer,

    V₀ = Molar volume of the solvent,

     χ  = Polymer solvent interaction.

 

The molecular weight between cross links Mc indicates the degree of cross linking. The higher the value of Mc the lower is the cross link density. The effective crosslink density of polymers is the total sum of chemical cross links. The molecular weight between cross links and cross link density of prepared polymers is shown in Table2.

 

Table 2. Cross linked properties of biopolymers

Sample	Crosslink density(mol cm-3)(x103)	Molecular weight between cross links mol-1	Weight loss %
IPNsVA	11.57	864.30	2.5
IPNsVP	13.14	761.03	6.6
IPNsMMA	15.76	634.51	5.2
IPNsMA	18.64	536.48	6.8

 

The cross link density of the present biopolymers influences the thermal stability. Cross linked IPNs of biopolymers exhibit higher thermal stability with lower weight loss are shown in figure 1.

 

 

Figure .1 : Molecular weight between cross links (Mol^-1)

FT-IR Spectral studies

The cross linking  of prepared biopolymers were confirmed through the FT-IR spectral analysis. The FT_IR spectrum of   the cured samples clearly indicates the significant disappearance of peak at 1,645 cm^-1 and reduction of peak at 981.59 cm^-1 for the unsaturated double bonds of acrylated epoxidized resins. This is due to the cross linking reaction of various co monomers. The strong peak observed at 1738cm^-1,1721cm^-1, 1718cm^-1 and1715cm^-1 indicates the ester groups of the cured samples are comprised predominantly .This is due to the tightness of the polymer network and reduced molecular mobility. The peak at 2947cm^-1, 2900cm^-1, 2817cm^-1 and 2850cm^-1 indicates extra hydrogen bonding interaction with the hydroxyl groups  present in the cured samples are shown figure.2.5.

 

Figure.2 FT-IR Spectral analysis of IPNsVA

 

Figure.3  FT-IR Spectral analysis of IPNsVP

 

Figure.4 FT-IR Spectral analysis of IPNs MMA

 

Figure.5 FT-IR Spectral analysis of IPNs MA

 

Table 3. Mechanical properties of biopolymers

Sample	Tensile strength(Mpa)	% Elongation at break	Tensile modulus(Mpa)	Molecular weight
IPNsVA	38.40 ± 2.4	54.01 ± 1.3	275 ± 5.4	536.48
IPNsVP	30.42 ± 1.3	45 ± 1.2	263 ± 3.3	634.31
IPNsMMA	28.90 ± 1.8	68.50 ± 4.80	377.70 ± 2.0	761.03
IPNsMA	24.36 ± 0.4	72.31 ± 1.2	397.61 ± 7.2	864.30

 

 

Mechanical properties

One of the most extensively used mechanical tests for polymers is the tensile or stress-strain test. The tensile strength of the polyesters are  largely influenced by the presence of aromatic groups, ether groups, long alkyl chain, dangling chains branching and cross linking and also degree of hydrogen bonding ¹⁸.The data on the mechanical properties of thermosetting polymers such as tensile strength,% elongation at break, tensile modulus are shown in Table 3.

 

The samples of biopolymers obtained using different co monomers have characteristics that vary from rubber to hard plastics. The result indicates that the products are typical thermosetting polymers with densely cross linked structures. Among this cross linked biopolymers vinyl acetate based polymers have higher tensile strength and tensile modulus which may be attributed to the higher cross link density. Brittle materials have low toughness, while ductile materials are very tough. In a tensile test, the tensile strength and elongation at break contribute the toughness of a material. This is attributed to the low molecular weight between the cross links and higher cross link density of the resulting biopolymers. The variations of tensile properties of the cross linked biopolymers with Molecular weight between cross links are shown in figure 6.

 

Figure : 6 Variation of Tensile properties with molecular weight between crosslink of various polymers.

 

Biodegradation studies:

Analysis of soil burial test

The synthetic plastics normally resist the microbial degradation and persist in the environment for longer times. The objective of this study was the isolation of the microbial strain having ability to adhere and degrade the vegetable oil based polymers. The films were buried in the soil mixed with municipal sewage sludge for six month. The biodegradability of vegetable oil based biopolymers was determined by visual changes in the polymers. The polymer IPNsVA shows highest weight loss and the sample IPNs MA shows the lowest weight loss in the soil burial degradation test. Triglyceride networks containing hydrolysable ester bonds especially linear diesters are biodegraded rapidly in soil. Kimura et al in their study of degradation of plastics was mainly caused by bacteria, fungi and that different soil conditions affected the rate of degradation of plastics¹⁹ .The percentage of weight loss was low between 30 and 40 days. After 40 days the degradation was rapid from this results triglycerides cross linked with hydrolysable bonds such as esters remain biodegradable²⁰. The weight loss % are shown in figure7.

 

Figure : 7Analysis of soil burial text

 

 

SEM Analysis

The SEM micrographs of polymers after soil burial degradation conditions test for 30 days were taken. The orginal polymer film exhibits a relative smooth surface without any pinholes and cavities (Figure8). However after 30 days in the soil (Figure9), large number of holes, cavities, and pin hole were observed in polymer film, indicated that the polymer surface was attacked by the microorganism under soil environment. Thus from the soil burial test the polymer synthesized is biodegradable and attacked by microorganisms.

A-IPNsVA 

B-IPNsVP

 

C-IPNsMMA                                                                          D- IPNsMA

Figure : 8 - Semphtographs of bio polymer before soil burial test

A-IPNsVA                                                                               B-IPNsVP

 

C-IPNsMMA                                                                          D- IPNsMA

Figure : 9 - Semphtographs of bio polymer after 30 days of soil burial test

 

 

Bacterial adhesion study

The prepared polymers were incubated at 35⁰c to 37⁰c with the test bacterial strains for 18 hours and number of bacteria adhered on the samples were determined. Degradation of several of these polymers proceeds through adsorption of the micro organism to the polymer surface followed by hydrolytic cleavage.S.aureus and E.coli species degrades the polymers Table4.

 

Table4.  Viable count/sample for biopolymer

Sample code	Number of bacterial adhered/sample
	E. coli  x106 cfu	S. aureus x106cfu
IPNs VA	4.9	1.8
IPNs VP	2.9	1.9
IPNs MMA	0.83	2.1
IPNs MA	0.52	1.7

 

Antimicrobial activity

The newly prepared biopolymers have been studied against bacteria and fungi strains .The IPNs VA showed potential anti bacterial and anti microbial activity against micro organisms (Table 5).Anti microbial activity IPNs VA and IPNs VP are shown figure 10 -11.

 

Table 5. Antimicrobial studies with zone of inhibition (nm)

Sample code	E.Coli	Candida albicans
IPNs VA	Nil	Nil
IPNs VP	5	7
IPNs MMA	6	8
IPNs MA	8	9
Gentamycin-10mg	25mm

 

 

Representative photograph of culture plates.

Strain:  C. albicans ATCC 10231

Strain: E. coli ATCC 25922

 

Figure : 11  Antimicrobial studies of  IPNsVP

 

CONCLUSION:

Natural oils are expected to be inexpensive renewable resources. Development of new polymeric materials from vegetable oil is highly desirable. The purpose of this work is to prepare high molecular weight of polymers and it would be alternative petroleum based polymeric materials. The present method of formation of IPNs of biopolymers showed a substantial improvement in polymer properties including cross linked density mechanical properties, as well as reduction in flammability, heat evolution and dimensional stability during processing. Soil and sewage sludge contain microorganisms that are able to bring about some degradation of synthetic polymers. The cured polymer films are biodegradable and used for agricultural films.

 

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Received on 08.09.2014         Modified on 19.09.2014

Accepted on 25.09.2014         © AJRC All right reserved