CHAPTER 2 EXPERIMENTAL TECHNIQUES

Transcription

1 59 CHAPTER 2 EXPERIMENTAL TECHNIQUES This chapter deals with the experimental procedures adopted in the present work for the synthesis and characterization of the IPNs, hydrogels and composites and evaluation of their physical properties. The polymers were characterized by spectral, thermal methods and microscopic techniques. 2.1 MATERIALS Sodium chloride, sodium hydroxide, ethyleneglycoldimethacrylate (EGDMA), N,N -methylenebisacrylamide (MBAAM), potassium per sulphate, 2-bromophenol B, hydrochloric acid, sulphuric acid etc., employed in the present study were all analytical grade and used as such without further purification Benzoyl peroxide (BPO) was recrystallised from a 1:1 mixture of methanol and chloroform and used. Dibutyltindilaurate (DBTDL) (MERCK) was used as a catalyst for the urethane reaction without further purification. Acrylamide (AAM) was purified by recrystallisation from benzene m.pt C. 2-Hydroxyethyl methacrylate (HEMA) (MERCK) was used as received without further purification. Polytetramethylene glycol TM (PTMEG) polyols based on tetramethylene ether backbone having molecular weights 1000 and 2000 having viscosities in the range of cps and cps (at 70 C) were obtained as commercial grade chemicals from BASF. The polyols were degassed at 70 C for 3hrs. Modified Polymeric 4, 4 -diphenyl methane diisocyanate (MDI), or polymeric MDI TM (commercially known as Rubinate 9433) was used as received from Huntsman. This material has isocyanate

2 60 equivalent weight of 132 and free NCO content of 31.09%. It was stored at C under nitrogen atmosphere prior to use. Toluene 2, 4-diisocyanate (Huntsman) was used without further purification and 1, 4-butanediol (BDO) from MERCK chemicals co were used without further purification. The reagents dibutylamine (MERCK), Cetyltrimethyl-ammonium-bromide (CTAB) (MERCK) and triethanolamine (MERCK) was used as such without further purification. 2.2 PURIFICATION OF SOLVENTS Solvents used in the present work include acetone, chloroform, methanol, ethanol, Dimethylformamide (DMF), Tetrahydrofuran (THF), benzene, toluene, water and isopropylalcohol were purified following procedures cited in literature (Furniss et al 1994). Acetone (SRL) (1L) was refluxed with successive quantities of potassium permanganate until the violet colour persisted. It was then dried with anhydrous potassium carbonate and distilled. The fraction boiling at C was collected. Chloroform (SRL) was washed with water, dried over anhydrous calcium chloride and distilled. The fraction boiling at 62±1 C was collected. N, N-Dimethylformamide (SRL) (1L) was dried overnight using 4Ǻ molecular sieves, filtered and then distilled at temperature C. The fraction boiling at this temperature was collected and used. Methanol (SRL) was treated with magnesium metal and distilled. The fraction boiling at 65±1 C was collected. Tetrahydrofuran (Qualigens) (1L) was dried with anhydrous calcium Sulphate. This was refluxed for 16h on a water bath and

3 61 distilled. The fraction boiling at 65±1 C was collected and stored in metallic sodium wire. Ethanol (SRL) (1L) was dried overnight using calcium carbonate and further refluxed for 1hr and then distilled at temperature C. The fraction distilled at this temperature was collected. Benzene (SRL) (1L) was dried over anhydrous CaCl 2. After decanting, benzene was distilled with the exclusion of moisture and then stored for sometime over sodium wire before further distillation. The fraction boiling at 80±1 C was collected and used. Isopropyl alcohol (SRL) (1L) was refluxed for 4 hrs using calcium oxide and then distilled. The distillate was allowed to stand over 5A molecular sieve for several days followed by further fractionation. The fraction boiling at C was collected and used. Toluene (SRL) (1L), 80ml conc.h 2 SO 4 was added and stirred mechanically at 30 C by occasional cooling. Toluene was then decanted and treated again with the acid till no more color was extracted. Finally, it was washed with water and dried over anhydrous CaCl 2 and then distilled. The fraction boiling at 110±1 C was collected and used. Double distilled water was used in the present study. 2.3 FILLERS FOR COMPOSITES Montmorillonite (MMT) i) Purification of Montmorillonite clay: A known amount (25g) of the crude montmorillonite clay (Fluka) was dispersed into 5 litres of 1N solution of NaCl with constant stirring for 24 hrs at 70 C.Upon centrifugation of the solution at high speed an opaque whitish gel accumulates in the bottom of the centrifuge tubes. The gel was isolated and washed several times with deionised water until no chloride was detected in the centrifugate which was ascertained by testing with one drop of 0.1 N AgNO 3 solution. The purified clay was dried at 70 C and stored in desiccator.

4 62 ii) Preparation of organic-mmt : 15g of the purified montmorillonite clay was dispersed into 1200ml of distilled water at 80 C. Cetyltrimethyl-ammonium-bromide (5.7g) dissolved in 300ml distilled water was poured in the hot mixture of the montmorillonite and water and stirred vigorously for 1hr at 80 C. A white precipitate formed, was isolated by filtration and washed several times with a hot water/ ethanol (1:1) mixture until no chloride was detected in the filtrate. The cetyltrimethyl-ammonium ion exchanged montmorrillonite was then dried 10 days at 75 C and ground into powder with a mortar and pestle. The organophillic clay was stored in a desiccator (Ma and Zhang et al 2001) Fiber Treatment i) Bagasse :The bagasse obtained from the local sources was washed with water and soaked in water for about two days, followed by drying at 80 C for 3 hrs. The dried bagasse fiber (25 g) was mixed with 500 ml of distilled water and boiled for 1hr. This boiling process was repeated for several times. The filter was purified by treating the fiber with 350ml of 1.25% H 2 SO 4 and 350ml of 1.25% NaOH solution for 1 hr at 70 C. It was again washed with boiling in water for 1hr to remove any adherent NaOH and kept overnight for air drying. Finally the filter was dried in hot air oven for 24 hrs at 110 C (Cao and Shibata et al 2006). ii) Wood flour fiber pretreatment : The wood flour was obtained from local sources and the wood was extracted with acetone using soxhlet apparatus and the extracted wood flour was dried to 1-2% moisture content using an oven at a temperature of 80 C and then stored in polyethylene bags until needed (Lu JZ and Wu Q et al 2000). 2.4 SYNTHESIS OF HYDROGELS Preparation of polyacrylamide hydrogel (PAAM)

5 63 Acrylamide monomer (AAM) (1g) and N,N methylenebisacrylamide (MBAAM) (1%) were dissolved in 2ml of deionised water. A 1% solution of potassium per sulphate (2ml) was added and the solution was flushed with nitrogen for 15 minutes to remove dissolved oxygen. Polymerization was carried out in a constant temperature bath at 55 C for 30 minutes. The crosslinked polyacrylamide gel obtained was washed with distilled water to remove unreacted monomer and the residual initiator by immersing the gel in deionised water for 24 hrs. The yield of the crosslinked gel was found to be 96% Preparation of starch incorporated polyacrylamide based hydrogels (PAMMS) Acrylamide monomer (AAM) (1g) and N,N methylenebisacrylamide (MBAAM) (1%) and different weight percent of starch (2% and 5%) with respect to acrylamide monomer were dissolved in 2ml of deionised water and 2ml of 1% potassium per sulphate solution was added. The solution was flushed with nitrogen for 15 minutes to remove dissolved oxygen. Polymerization was carried out in a constant temperature bath at 55 C for 30 minutes. The crosslinked starch grafted polyacrylamide gel obtained was washed with distilled water to remove unreacted monomer and the residual initiator by immersing the gel in deionised water for 24 hrs. The yield of the crosslinked gel was found to be 97% Preparation of poly (2-hydroxyethylmethacrylate) films (PHEMA) Films of PHEMA were prepared by initially dissolving ethylene glycol dimethacrylate (EGDMA, 0.1%w/w) and benzoyl peroxide (1%w/w) in HEMA monomer with stirring. The solution.was injected into moulds composed of two glass plates which were separated by rubber spacers and clamped using steel clips. The moulds were then maintained at 60 C for 1 hr

6 64 to ensure homogeneous dispersion of the components and polymerized at 90 C for 1 hr. The formed films were thoroughly washed with deionised water to remove any unreacted monomer and the air dried films were used for further characterization studies (Jones and McLaughlin et al., 2005). The yield of the crosslinked film was found to be 95%. 2.5 SYNTHESIS OF SIMULTANEOUS SEMI- INTERPENETRATING POLYMER NETWORKS The semi-ipn was prepared in two stages (a) Preparation of polyurethane prepolymer (b) Preparation of poly(2-hydroxyethyl methacrylate) incorporated polyurethane based semi-interpenetrating polymer networks Preparation of NCO terminated polyurethane prepolymer (PTEMU-PP) In the preparation of NCO-terminated polyurethane prepolymer (Scheme 2.1) varying NCO/OH ratio of modified polymeric MDI and polytetramethylene ether glycol (PTMEG) polyol of molecular weight 1000 were added slowly with stirring in a three necked flask equipped with a mechanical stirrer and a very small amount of catalyst DBTDL was added and 1, 4-butanediol (BDO) was added for chain extension and the reaction was carried out at 90 C-100 C for 3hrs by purging nitrogen gas. The completion of the reaction and the absence of the monomer were determined by the di-n-butylamine titration method when the isocyanate group content of the reaction mixture reached the theoretical value. This was also confirmed through a characteristic absorption peak at 2270cm -1 for NCO group.

7 65 The same process was adopted for the preparation of NCO terminated polyurethane prepolymer using polyether polyol of molecular weight The prepolymers were obtained in yields of approximately 95% with respect to the polyether polyols. The composition were shown in Table Preparation of poly(2-hydroxyethylmethacrylate) incorporated polyurethane based semi-interpenetrating polymer networks (PTEMU-PP/PHEMA semi- IPNs) IPNs were synthesized by charging the polyurethane prepolymer (PTEMUPP1000) in different proportions (Table 2.1) into a three necked round-bottomed flask.to this, the mixture of HEMA monomer, EGDMA (0.1%w/w) and BPO (1%w/w) was added and (0.1%w/w) triethanolamine (for chain extension and curing) was added and dissolved in 20 wt% of THF. The mixture was stirred at room temperature for 15 minutes to form a homogeneous solution. The temperature was then increased to 70 C to initiate HEMA polymerization. After stirring for 1hr, the viscous solution was degassed to remove trapped bubbles and poured into a glass mould kept in a preheated oven maintained at 70 C. It was kept at this temperature for 24 hr and at 120 C for 6 hr to facilitate the complete network formation. The film thus formed was cooled slowly and removed from the mould and the dried films were used for further studies. The same process was adopted for the polyurethane prepolymer of polyether polyol of molecular weight 2000.The reaction scheme is shown in Scheme 2.1. The different compositions of PHEMA incorporated PTEMU-PP1000 and PTEMU-PP2000 semi-ipns are listed in Table 2.1.

8 66 Scheme 2.1 Poly(2-hydroxyethylmethacrylate) incorporated polyurethane based semi-interpenetrating polymer networks (PTEMU- PP/PHEMA semi-ipns)

9 67 Table 2.1 Compositions used in HEMA incorporated polyurethane based semi-ipns Code of semi-ipns Molecular weight of Polyurethane prepolymer(m w ) NCO/OH Ratio a Polyurethane prepolymer (PTEMU-PP) (Mole %) *Monomer (HEMA) (Mole %) PTEMU- PP1000/PHEMA semi-ipn PTEMU- PP2000/PHEMA semi-ipn * 0.1% EGDMA& 1% BPO w.r.t Monomer; a=0.1% TEA Preparation of polyacrylamide incorporated polyurethane based semi-interpenetrating polymer networks (PTEMU-PP/PAAM semi- IPNs) The semi-ipns were prepared in two steps. The first step involved the NCO-terminated polyurethane prepolymer (Scheme 2.2) was prepared based on PTMEG polyol of molecular weight 1000 & 2000 as per the procedure described in section In the Second step the IPNs were synthesized by charging the polyurethane prepolymer in different proportions (Table 2.2) into a three necked round-bottomed flask.to this, the mixture of acrylamide (AAM) monomer, N, N -methylenebisacrylamide (MBAAM) (O.01%w/w) and BPO (0.5%w/w) was added and dissolved in 20 wt% of THF. The mixture was stirred at room temperature for 15 minutes to form a homogeneous solution.

10 68 The temperature was then increased to 70 C to initiate acrylamide polymerization. After stirring for 1hr, the viscous solution was degassed to remove trapped bubbles and poured into a glass mould kept in a preheated oven maintained at 60 C. It was kept at this temperature for 24 hr and at 100 C for 2 hr to facilitate the complete network formation. The film thus formed was cooled slowly and removed from the mould and the dried films were used for further studies. The same process was adopted for polyether polyol of molecular weight Scheme 2.2 Polyacrylamide incorporated polyurethane based semi- interpenetrating polymer networks (PTEMU-PP/PAAM semi-ipns)

11 69 Table 2.2 Compositions used in Acrylamide incorporated polyurethane based semi-ipns Code of semi-ipns PTEMU- PP1000/PAAM semi-ipn PTEMU- PP2000/PAAM semi-ipn Molecular weight of Polyurethane prepolymer(m w ) NCO/OH Ratio Polyurethane prepolymer (PTEMU-PP) (Mole %) *Monomer Acrylamide (AAM) (Mole %) * 0.01% MBAAM& 0.5% BPO w.r.t Monomer 2.6 SYNTHESIS OF NANOCOMPOSITES The polyurethane nanocomposite was prepared in two stages: (a) Preparation of polyurethane prepolymer (b) Preparation of pure montmorillonite or CTAB modified montmorillonite incorporated polyurethane based semi-interpenetrating polymer networks Preparation of NCO-terminated polyurethane prepolymer (PTETU-PP) In the preparation of NCO-terminated polyurethane prepolymer (Scheme 2.3) varying NCO/OH ratio of toluene diisocyanate (TDI) and polytetramethylene ether glycol (PTMEG) diol of molecular weight 2000 were added slowly with stirring in a three necked flask equipped with a mechanical stirrer and a very small amount of catalyst DBTDL was added and 1, 4-butanediol (BDO) was added for chain extension and the reaction was carried out at 40 C for 2 hrs by purging nitrogen gas. The completion of the

12 70 reaction and the absence of the monomer were determined by the di-nbutylamine titration method when the isocyanate group content of the reaction mixture reached the theoretical value. This was also confirmed through a characteristic absorption peak at 2270cm -1 for NCO group. The composition and notations of the polyurethane prepolymer were shown in Table 2.3. Hard segment phase Soft segment phase Nanocomposites Layered silicate Hard segment Soft segment Scheme 2.3 Synthesis of montmorillonite incorporated polyurethane based nanocomposites

13 Preparation of polyurethane/montmorillonite semi-ipn nanocomposites (PU/MMT semi-ipn ) In the preparation of unmodified montmorillonite /polyurethane IPN nanocomposite, different amounts of unmodified montmorillonite were mixed with 10 ml of THF and the mixture was added to the previously prepared NCO-terminated polyurethane prepolymer (Table 2.3). To this, the mixture of HEMA monomer, EGDMA (O.1%w/w) and BPO (1%w/w) was added and (0.1%w/w) triethanolamine (for chain extension and curing) was added. The mixture was stirred at room temperature for 15 minutes to form a homogeneous solution. The temperature was then increased to 70 C to initiate HEMA polymerization. After stirring for 1hr, the viscous solution was degassed to remove trapped bubbles and poured into a glass mould kept in a preheated oven maintained at 70 C. It was kept at this temperature for 24 hr and at 120 C for 6 hr to facilitate the complete network formation. The film thus formed was cooled slowly and removed from the mould and the dried films were used for further studies Preparation of polyurethane/ctab modified montmorillonite semi-ipn nanocomposites (PU/ CTAB-MMT semi-ipn) In the preparation of organic montmorillonite /polyurethane IPN nanocomposite, different amounts of organic montmorillonite were mixed with 10 ml of THF and the mixture was added to the previously prepared NCO-terminated polyurethane prepolymer (Table 2.3). To this, the mixture of HEMA monomer, EGDMA (O.1%w/w) and BPO (1%w/w) was added and (0.1%w/w) triethanolamine (for chain extension and curing) was added. The mixture was stirred at room temperature for 15 minutes to form a homogeneous solution. The temperature was then increased to 70 C to initiate HEMA polymerization. After stirring for 1hr, the viscous solution was degassed to remove trapped bubbles and poured into a glass mould kept in a

14 72 preheated oven maintained at 70 C. It was kept at this temperature for 24 hr and at 120 C for 6 hr to facilitate the complete network formation. The film thus formed was cooled slowly and removed from the mould and the dried films were used for further studies. Table 2.3 Compositions used in the preparation of montmorillonite incorporated polyurethane based Nanocomposites Code of Nanocomposites a,b,c Polyurethane prepolymer (PTETU-PP) (Mole %) *Monomer (HEMA) (Mole %) Unmodified Montmorilonite (MMT) Weight % PTETU-PP2000/ PHEMA semi-ipn PTETU-PP2000/ PHEMA/ MMT-2 NC PTETUPP2000/ PHEMA/ MMT-5 NC PTETU-PP2000/ PHEMA/ CTAB- MMT-2 NC PTETU-PP2000/ PHEMA/ CTAB- MMT-5 NC CTAB Modified Montmorilonite (CTAB-MMT) Weight % a-molecular weight of polyurethane prepolymer=10,000; b-nco/oh Ratio=2.2; c-0.1%tea ;* 0.1% EGDMA& 1% BPO w.r.t Monomer 2.7 SYNTHESIS OF FIBER REINFORCED COMPOSITES The polyurethane fiber reinforced composite was prepared in two stages: (a) Preparation of polyurethane prepolymer (b) Preparation of different fibers incorporated polyurethane based semi-interpenetrating polymer networks

15 Preparation of NCO-terminated polyurethane prepolymer (PTETU-PP) The NCO-terminated polyurethane prepolymer (Scheme 2.4) was prepared based on PTMEG polyol of molecular weight 2000 as per the procedure described in section Scheme 2.4 Synthesis of fiber reinforced polyurethane based Composites

16 Preparation of polyurethane/bagasse fiber composite (PU/BAGF) In the preparation of polyurethane /bagasse fiber composite, different amounts of bagasse fiber were mixed with 10 ml of THF and the mixture was added to the previously prepared NCO-terminated polyurethane prepolymer (Table 2.4). To this, the mixture of HEMA monomer, EGDMA (O.1%w/w) and BPO (1%w/w) was added and (0.1%w/w) triethanolamine (for chain extension and curing) was added. The mixture was stirred at room temperature for 15 minutes to form a homogeneous solution. The temperature was then increased to 70 C to initiate HEMA polymerization. After stirring for 1hr, the viscous solution was degassed to remove trapped bubbles and poured into a glass mould kept in a preheated oven maintained at 70 C. It was kept at this temperature for 24 hr and at 120 C for 6 hr to facilitate the complete network formation. The film thus formed was cooled slowly and removed from the mould and the dried films were used for further studies Preparation of polyurethane /wood flour fiber composite (PU/WFF) In the preparation of polyurethane /wood flour fiber composite, different amounts of wood flour fiber were mixed with 10 ml of THF and the mixture was added to the previously prepared NCO-terminated polyurethane prepolymer (Table 2.4). To this, the mixture of HEMA monomer, EGDMA (O.1%w/w) and BPO (1%w/w) was added and (0.1%w/w) triethanolamine (for chain extension and curing) was added. The mixture was stirred at room temperature for 15 minutes to form a homogeneous solution. The temperature was then increased to 70 C to initiate HEMA polymerization. After stirring for 1hr, the viscous solution was degassed to remove trapped bubbles and poured into a glass mould kept in a preheated oven maintained at 70 C. It was

17 75 kept at this temperature for 24 hr and at 120 C for 6 hr to facilitate the complete network formation. The film thus formed was cooled slowly and removed from the mould and the dried films were used for further studies Preparation of polyurethane /glass fiber reinforced composite (PU/GF) In the preparation of polyurethane /glass fiber reinforced composite, different amounts of glass fiber were mixed with 10 ml of THF and the mixture was added to the previously prepared NCO-terminated polyurethane prepolymer (Table 2.4). To this, the mixture of HEMA monomer, EGDMA (O.1%w/w) and BPO (1%w/w) was added and (0.1%w/w) triethanolamine (for chain extension and curing) was added. The mixture was stirred at room temperature for 15 minutes to form a homogeneous solution. The temperature was then increased to 70 C to initiate HEMA polymerization. After stirring for 1hr, the viscous solution was degassed to remove trapped bubbles and poured into a glass mould kept in a preheated oven maintained at 70 C. It was kept at this temperature for 24 hr and at 120 C for 6 hr to facilitate the complete network formation. The film thus formed was cooled slowly and removed from the mould and the dried films were used for further studies Preparation of polyurethane/nylon fiber reinforced composite (PU/NF) In the preparation of polyurethane /nylon net reinforced composite involved two stages. First the preparation of polyurethane prepolymer, secondly the preparation of HEMA incorporated polyurethane semi-ipns. The net was cut to desired length and breadth. The prepared HEMA incorporated polyurethane semi-ipns was poured into the nylon net in a glass mould and the glass mould was kept in a preheated oven maintained at 70 C.

18 76 It was kept at this temperature for 24 hr and at 120 C for 6 hr to facilitate the complete network formation. The film thus formed was cooled slowly and removed from the mould and the dried films were used for further studies. Table 2.4 Compositions used in the preparation of polyurethane based fiber reinforced Composites Code of Composites PTETU-PP2000/ PHEMA semi-ipn PTETU-PP2000/ PHEMA/BAGF-2 PTETUPP2000/ PHEMA/BAGF-5 PTETU-PP2000/ PHEMA/ WFF-2 PTETU-PP2000/ PHEMA/ WFF-5 PTETU-PP2000/ PHEMA/ GF-2 PTETU-PP2000/ PHEMA/ GF-5 a,b,c Polyurethane prepolymer (PTETU-PP) (Mole %) *Monomer (HEMA) (Mole %) Bagasse Fiber Weight % Wood flour fiber Weight % Glass fiber Weight % a-molecular of polyurethane prepolymer=10,000, b-nco/oh Ratio=2.2 c-0.1%tea; * 0.1% EGDMA& 1% BPO w.r.t Monomer 2.8 PHYSICOCHEMICAL CHARACTERIZATION Wet chemical analysis The free NCO content of PTEMU-PP, PTETU-PP were determined by reacting the sample dissolved in toluene with known excess amount of n-butyl amine and titrating the excess unreacted n-butyl amine against standard HCl. The free NCO content (%) was calculated with reference to

19 77 blank and evaluated as ((Blank titre value-volume of HCl) x Concentration of HCl x 4.2/ weight of sample in grams) Analysis of isocyanates The most important characteristic of polyisocyanates is NCO content. It is determined according to ASTM D by dissolving isocyanate in the mixture of toluene and dibutylamine (DBA). DBA reacts with isocyanate and the excess is titrated with HCl solution. The NCO content is calculated from the expression: %NCO = [(B-S) N x 4.202]/W where B is the number Of ml of HCl used for titration of the blank, S is the number of ml of HCl used for titration of the sample, N is the molarity of HCl solution, and W is the weight of the sample in grams Analysis of polyols The principle property measured in polyols is hydroxyl content. According to ASTM D , hydroxyl group content is determined by acetylation and the excess of acid back titrated with a base. The acetylating agent is usually a solution of acetidc anhydride in pyridine. Acetylation is carried out at 100 C. Unreacted anhydride is then converted with water into acid and titrated with 1N NaOH. Hydroxyl content is usually expressed as hydroxyl number (OH number), which is defined as milligrams of KOH (M KOH =56.1) used for titration of one gram of the sample. OH number (mg KOH/g) =56.1(B-A) N/W

20 78 where A is the number of ml NaOH, B is number of ml NaOH used for titration of blank, N is molarity of the NaOH solution, and W is the weight of the sample in grams. Hydroxyl content in percent can be calculated from theproporation which takes into account that OH number of 56.1 correspond to1.7% OH groups. Thus, the content of OH groups, X (%) = 1.7Y/56.1 where Y is OH number expressed in mg KOH/g Infrared spectra Fourier transform infrared (FTIR) spectra were recorded by using a KBr pellet on a Spectrum one FTIR (Perkin-Elmer instruments, USA) in the wave number range cm Differential scanning calorimetry (DSC) Differential scanning calorimetry (DSC) thermograms were recorded using a DSC 200PC NETZSCH-Geratebau Gmbh thermal analyzer.the heating rate was 20 C min -1 in the temperature range of -150 C to 300 C Thermogravimetric analysis (TGA) Thermo gravimetric analysis (TGA) was performed on a STA 409PC NETZSCH-Geratebau Gmbh thermal analyzer in nitrogen atmosphere at a heating rate of 20 C min -1.

21 Gel Permeation Chromatography (GPC) The molecular weight estimations were carried out on a JASCO GPC chromatograph model MX fitted with PL gel 5µm mixed C columns, 300x 7.5mm, in tetrahydrofuran (THF) with a flow rate of 1mL min -1 at 30 C using refractive index (RI) detector. The molecular weights were calculated from the calibration curve established for polystyrene standards Water absorption The water absorption was determined by immersing the cut membranes in a beaker of water at 37 C. The membranes, with a thickness of 1mm were cut into circular disks of 20 mm diameter by using a sharp-edged stainless steel knife. The drained samples were weighed every 10 min until they attained the maximum water content. The water absorption (WS) was calculated by using the formula W2 W1 W.S. x100 W1 where, W 1 and W 2 are the weights of the sample before and after the test Swelling behavior The dried samples were immersed in an excess of deionised water until swelling equilibrium was attained. The weight of swollen sample (W s ) was determined after removing the surface water by blotting with filter paper. Dry weight (W d ) was determined after drying the gel in a vacuum oven for 1 day at room temperature. The equilibrium water content was calculated using the formula

22 80 EWC (%) = [W s -W d / W d ] x100 were, W s and W d are the weights of the water absorbed and the dry samples respectively Swelling behavior at different ph values Equilibrium water contents were measured at ph 4.2, ph 7 and ph 9.2 using appropriate buffer solution. Preweighed, dry samples were immersed in ph 4.2, 7 or 9.2 buffer solutions until they swelled to equilibrium. It was confirmed that 24 hr equilibration was enough to reach the equilibrium swelling of disks. After excessive surface water was removed by filter paper, the weights of swollen sample were measured.the equilibrium water content was calculated from the formula mentioned in section Hydrolytic stability measurement The hydrolytic stability was determined as follows: 12 preweighed dry films were saturated with phosphate buffer solution (ph 7.4) and stored in sealed glass vials and kept in an oven at 80 C. Three samples were removed after 3 rd day, similarly each three samples were removed after 5day, 7day and 14 day respectively. They were washed with distilled water and dried at 80 C for 16 hrs. The percent weight loss of sample after different periods of testing were obtained by comparing the weight of dry sample before and after testing X-ray diffractometer X-ray diffractograms were recorded on samples (composites/ipns or hydrogels with a Pan analytica X-pert diffractometer using Cuk α (λ=0.154nm) radiation.

23 Tensile strength and Elongation The tensile strength and elongation of the polymer samples were tested using a Universal Testing Machine (Hounsfield, UK) at a crosshead speed of 5mm/min as per ASTM D638 standard. For test specimens, the standard dumblebell shaped test specimens were used so that the geometry ensures that only tensile stresses occur which act parallel to the surface and perpendicular to the cross sectional area. Moreover, rupture of the test specimen through stress concentration in the grip area was avoided. Both dried and swollen samples were measured; the tensile specimen, 1mm thick and 6mm wide were cut from the sheet. The elongation at break (ultimate elongation) and the corresponding stress (breaking stress) were used as characteristic values of a material. The tensile strength was determined using the formula, Tensile strength (kg/cm 2 ) = Breaking load in kgs Thickness in cm x width in cm Elongation at break was calculated by taking the difference between the original length and the length at the time of rupture under the tension force. The elongation is measured simultaneously with the measurement of tensile strength. Percentage elongation at break is given by Increase in length in cm Percentage elongation at break = x 100 Original length in cm Compressive strength The compressive strength of the swollen polymer samples were tested using a Universal Testing Machine (Hounsfield, UK) at a crosshead speed of 5mm/min as per ASTM D695-02A standard. The hydrogel samples

24 82 were prepared as per the ASTM standard measurement and tested. The hydrogel samples were cut into certain lengths of cylindrical shape and swollen in distilled water to equilibrium. The swollen samples were used for testing by mounting on the UTM instrument Hardness Hardness was tested in Hardness Shore D tester as per ASTM D Spring-loaded pins are pressed into the test specimen and the penetration depth under a standardized load was taken as a measurement of the hardness of the sample Scanning Electron Microscopy (SEM) SEM observations were made with Leo Stereoscan 440 Scanning electron microscope. The cryogenically fractured film in liquid nitrogen was mounted vertically on the SEM stub by silver adhesive paste. The specimens were sputter coated with gold to avoid electrostatic charges and to improve image resolution before being examined by the electron microscopy.