Cloisite-g-Methacrylic Acid Copolymer Nanocomposites by Graft from

Article pubs.acs.org/IECR

Cloisite-g-Methacrylic Acid Copolymer Nanocomposites by Graft from Method for Leather Processing Sellamuthu Nagappan Jaisankar,*,† Sathya Ramalingam,† Hariharan Subramani, Ranganathan Mohan,‡ Palanivel Saravanan,§ Debasis Samanta,† and Asit Baran Mandal† †

Polymer Lab, ‡Shoe Design and Development Centre, §Tannery, Council of Scientific and Industrial Research (CSIR)-Central Leather Research Institute (CLRI), Adyar, Chennai 600 020, India ABSTRACT: A series of novel facile water dispersible cloisite-g-methacrylic acid copolymers were prepared by graf t f rom method. These graft copolymers were applied on goat skin before and after neutralization processes to produce lightweight, soft, grain tight, and water vapor permeable leather. All the graft copolymers and polymethacrylic acid (PMA) were thoroughly characterized by spectroscopic methods and thermal property changes. The intercalated cloisite-g-methacrylic acid copolymer nanocomposites exhibit a decreasing trend in viscosities with increase in the weight percentage of cloisite. The cloisite-gmethacrylic acid (C-g-MA) copolymers exhibit better thermal stability. All the nanocomposites showed a shear-thickening flow behavior. The stress−strain measurements of leather treated with nanocomposite samples reveal an increase in modulus property with the increase in cloisite content. The low weight percentage graft copolymers nanocomposite treated leathers are lightweight, have better smoothness, and show uniformity in feel, fullness, and load at grain crack.

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INTRODUCTION

in leather making process and other applications without impairing its natural characteristics.14,15 Recently, a new generation of nanomaterial-based synthetic tanning agents have been reported from our lab12 and trials have been performed up to technical scale that showed double efficiency of the existing products in the market. Nanomaterials can be classified in to several different classes, like nanoclusters, nanopowders, nanocrystals, nanoclays, etc. that is 1−10 nm size in at least one dimension. Among them, nanoclays have high combination potential with polymers to form polymer clay nanocomposite materials (PCN).9 The PCN have received a great deal of attention16 in leather processing because of the fact that nanocomposites exhibit gains in structural, thermal, mechanical properties, UV-resistance, fungi resistance, and antiradiation without a significant loss in impact or clarity of the leather.17,18 Recently, many researchers have reported on preparation and characterization of polymer−clay nanocomposites based on single-polymer matrices.19 Very recently, application of polymeric nanocomposite materials for leather tanning processes has been reported.20 The most commonly used methods to prepare nanoparticlefilled polymer for leather coatings are solution blending and in situ polymerization.17 Synthetic retanning agents like syntans, resins, or polymers of acrylic acid (AA) and methacrylic acid (MA) have found use in the leather industry as anionic syntans and have been extensively reported.21−23 Acrylic resin was applied as retanning agent successfully revealing a series of excellent properties: good adhesion to pigments; strong adhesion to leather and soft, transparent, and elastic films. Furthermore, there are some better sanitary

In recent years, polymer/clay nanocomposites have generated much interest because of their enhanced properties at lower nanofiller loading as compared with conventional micrometersize fillers.1−3 The understanding of the behavior of these composites is important to control the interactions at the nanofiller/matrix interface. Various recent reports focused on the chemical attachment of polymer chains on the cloisite surfaces.4,5 Two methods can be used to graft polymer chains on nanoparticles. The first method is the “graf t onto” method, where the polymer end group reacts with nanoparticle surface. The second method is “graf t f rom”, where the monomer chain grows up in situ from the surface.6 In the polymer/nanoclay systems, the restrictive environment of the polymer chain inside the clay gallery greatly affects (i) the molecular relaxation, (ii) mobility, and (iii) crystallization.7 The low polar amorphous polymers like polystyrene (PS) and poly(methyl methacrylate) (PMMA) can form nanocomposites that tend to form intercalated structures.8,9 The ecological concerns related to synthetic retanning agents is “free formaldehyde” in the product and subsequently in the leather that is developed and reported from our lab.10,11 Polymers, which are usually used as conventional syntans, are manufactured by dispersion polymerization.12 It has been reported that inorganic additives were originally introduced into polymer matrix as fine solids to act either as fillers or reinforcing agents.3 These inorganic fillers were used to dilute and hence to reduce the amount of the final polymers used in shaped structures, thereby lowering the cost of the polymer matrix. We have recently reported the synthesis of nanosilica for transparent biocompatible hydrophobic coatings on biological substrates such as leather.13 Several recent reports suggested that polymers comprised with nanomaterials (such as nanoclays, biomaterials) have an immense application potential © 2012 American Chemical Society

Received: Revised: Accepted: Published: 1379

February 2, 2012 October 8, 2012 December 24, 2012 December 24, 2012 dx.doi.org/10.1021/ie300290g | Ind. Eng. Chem. Res. 2013, 52, 1379−1387

Industrial & Engineering Chemistry Research

Article

specialties than casein resin24 such as light fastness and rub fastness and some better properties than nitrocellulose and polyurethane leather coatings as well.25 The best method to overcome the unstable properties of the acrylic resin at different temperatures was modified by using copolymerization, graft copolymerizations,3 or cross-linking of acrylic monomers. Using these methods, the heat and solvent resistance of the polymers can be improved.26 There are several reports on polymeric nanocomposites composed of styrene (St) and maleic anhydride (MAH) for processing leather in recent years.29 In order to optimize synthetic tanning/retanning agents from an environmental point of view, a concept for high efficiency product was introduced. In recent years, a handful of examples of polymethylmethacrylic acid−clay nanocomposite materials for different applications have been reported. For example Nayak and others27 reported that PMMA nanocomposites can be fabricated using different weight percentage of nanoclays and PMMA in a Haake Rheocord for the improvement of fire retardancy. Fang and others reported that via γ-ray irradiation polymerization, poly(methyl methacrylate) (PMMA)/clay nanocomposites can be prepared with reactive modified clay and nonreactive clay for the enhancement of thermal properties.28 In this paper, we report a new type of water dispersible cloisite grafted methacrylic acid nanocomposites prepared by graft copolymerization method and its application as retanning of goat skins before and after neutralization. The application test shows that the nanocomposites induces the higher shrinkage temperature, lightening of weight, increase in thickness, uniformity in feel, fullness, grain tightness, softness, smoothness of surface leather and cutting value compared with the traditional polymers or copolymers retanned leather.

complete by 4 h, which was confirmed by absence of any monomer smell and from percentage solids content. The temperature of the reactor was then brought down to room temperature by circulating cold water and the resultant nanocomposite solution was adjusted to pH of 3−5 with NaOH. The above experiment was repeated with different weight (0.1, 0.5, 1.0, 2.0, and 3.0 wt %) percentage of cloisite (see Table 1). The optimized products were used as retanning agents before and after neutralization in leather processing (see Table 2). Table 1. Code and Compositions of Cloisite-g-Methacrylic Acid Copolymers s. no. 1 2 3 4 5 6 7

code SH SH SH SH SH SH SH

00 12 20 21 22 23 24

compositions cloisite 10A polymethacrylic acid (PMA) PMA + 0.1% cloisite 10A PMA + 0.5% cloisite 10A PMA + 1.0% cloisite 10A PMA + 2.0% cloisite 10A PMA + 3.0% cloisite 10A

Characterization of Grafted Copolymers and Copolymers Retanned Leather. ATR-FTIR (Nicolat Impact 400 spectrophotometer) was used for providing the proof of grafting of cloisite-g-methacrylic acid copolymers and nanocomposite treated leathers. Differential scanning calorimetry (DSC) was performed to determine the transition temperatures like glass transition temperature (Tg), melting temperature (Tm), and crystallization temperature (Tc) of the copolymers and homopolymer. DSC of the samples were carried out using Q2000 TA Instruments with ramp 15 °C/min from room temperature to 300 °C in a nitrogen atmosphere. Thermogravimetric analysis (TGA) of the sample was carried out using a Q50 TA Instruments, ramp 15 °C/min from room temperature to 600 °C in a nitrogen atmosphere. Weight loss of these materials as a function of temperature was recorded using this study. The viscosity of the PCN was done in Brookfield DV-E viscometer with different spindle nos. (nos. 07, 06, 05, 04, and 03), different speed (20, 30, 50, 60, and 100 rpm). Rheological investigations were performed by Anton Paar MCR 52 Rheometer device using a cone and plate geometry measuring system with an angle (α) of 1.003°. The flow behavior of the PMA and graft copolymer nanocomposites were tested by rotational controlled shear stress condition, where the viscosity (η) of the samples were measured as a function of increasing shear stress (ι).

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EXPERIMENTAL SECTION Materials. Nanoclays (Cloisite 10 Å, supplier designation dimethyl, benzyl, hydrogenated tallow quaternary ammonium chloride organoclay, specifications 125 CEC, organic content = 36.9 wt %, d001 spacing = 1.95 nm), supplied by Southern Clay Products Inc. (Texas, USA) were used. Prior to graft, the cloisite nanoclays were dried in a vacuum oven at 80 °C for at least 12 h. Methacrylic acid (MA) was obtained from Loba Chemie Pvt Ltd., potassium persulfate (K2S2O8), (Merck Specialties Private Limited), sodium metabisulfite (Na2S2O5), (Merck Specialties Private Limited), sodium hydroxide (RANBAXY Laboratories Limited), methanol (SISCO Research Laboratories Pvt. Ltd.). All the above chemicals were used as received. Preparation of Methacrylic Acid Grafted to Cloisite. A 1 kg reactor with flange containing four inlets for nitrogen gas, thermometer, stirrer, and additional inlets for catalyst and monomer were used for this experiment. Nanoclay (Cloisite10 Å) with 0.1 wt % of redox initiators K2S2O8 and Na2S2O5 was dispersed in distilled water while stirring the contents continuously with a stirrer at a rate of 120 rpm for 1 h. The temperature of dispersion was raised to 80−90 °C. Calculated quantity of MA and K2S2O8 (3−5% v/v) in distilled water were added to the reactor drop by drop through the respective inlets for monomer and initiator. The inlet was adjusted in such a way that both monomer and initiator were added to the dispersion drop by drop over the period of 45 min while stirring the mixture continuously. The reaction was allowed to proceed for 4 h. It was found that the consumption of monomer was

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RESULTS AND DISCUSSION Determination of Percent Grafting and Grafting Efficiency of Grafted Copolymers.3 A number of the experiments were carried out to optimize the polymeric conditions to get the desired results. To determine the percent grafting (% PG) and grafting efficiency (% GE), after completing the polymerization, the product was extracted using Soxhelt apparatus with methanol to remove the homopolymer. When the extraction time was complete, the sample was carefully transferred into an evaporating dish and the sample was weighed. The percent PG and GE were calculated according/to the formulas given in eqs 1 and 2. 1380

dx.doi.org/10.1021/ie300290g | Ind. Eng. Chem. Res. 2013, 52, 1379−1387


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Table 2. Retanning Formulations for Goat Skin process before after acid wash

rechroming

washing

neutralization

washing

retanning, dyeing and fat liqoring

control

experiment

after neutralization

before neutralization



water 300% Tergolix A 0.50% formic acid 0.50% W/D/W water 100% Catalix L 1% 10′ + basic chromium sulfate 5% 30′ water 50% at 60 ◦C sodium formate 1% 10′ sodium bicarbonate 1% 3*10′ check pH-3−4 +60′ water 200% 5′ pile O/N water 150% Vernatan AKM 2% formic acid 0.50% 30′ sodium bicarbonate 0.75% 3*5′ check pH-4.8−5 45′

water 300% Tergolix A 0.50% formic acid 0.50% W/D/W water 100% Catalix L 1% 10′ + basic chromium sulfate 5% 30′ water 50% at 60 ◦C sodium formate 1% 10′ sodium bicarbonate 1% 3*10′ check pH-3−4 +60′ water 200% 5′ pile O/N water 150% samples 5% 30′ Vernatan AKM 2% formic acid 0.50% 30′ sodium bicarbonate 0.75% 3*5′ check pH-4.8−5 45′ water 200% 3*5′ water 100% Tanicor A 4% Tergotan ARF 4% 30′ Tanicor DRF 4% Granogin TA 2% Chestnut 2% 30′

water 300% Tergolix A 0.50% formic acid 0.50% W/D/W water 100% Catalix L 1% 10′ + basic chromium sulfate 5% 30′ water 50% at 60 ◦C sodium formate 1% 10′ sodium bicarbonate 1% 3*10′ check pH-3−4 +60′ water 200% 5′ pile O/N water 150% 30′ Vernatan AKM 2% formic acid 0.50% 30′ sodium bicarbonate 0.75% 3*5′ check pH-4.8−5 45′

water 300% Tergolix A 0.50% formic acid 0.50% W/D/W water 100% Catalix L 1% 10′ + basic chromium sulfate 5% 30′ water 50% at 60 ◦C sodium formate 1% 10′ sodium bicarbonate 1% 3*10′ check pH-3−4 +60′ water 200% 5′ pile O/N water 150% samples 5% 30′ Vernatan AKM 2% formic acid 0.50% 30′ sodium bicarbonate 0.75% 3*5′ check pH-4.8−5 45′ water 200% 3* 5′ water 100% Tanicor A 4% Tergotan ARF 4% 30′ Tanicor DRF 4% Granogin TA 2% Chestnut 2% 30′

water 200% 3*5′ water 100% samples 5% Tanicor A 4% Tergotan ARF 4% 30′ Tanicor DRF 4% Granogin TA 2% Chestnut

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water 200% 3*5′ water 100% samples 5% Tanicor A 4% Tergotan ARF 4% 30′ Tanicor DRF 4% Granogin TA 2% Chestnut



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Table 2. continued process

control

before after



2% 30′ Coralon OT 1% 10′ + dye 3% run for 30′ water 100% at 60 °C + fat liquor 3% 30′ + formic acid 2% 3*5 + 45′ check the exhaustion water 100% dye 2% run for 30′ 2% formic acid 3*5 +45′ rinse and pile O/N

top dyeing

experiment

Coralon OT 1% 10′ + dye 3% run for 30′ water 100% at 60 °C + fat liquor 3% 30′ + formic acid 2% 3*5 + 45′ check the exhaustion water 100% dye 2% run for 30′ 2% formic acid 3*5 +45′ rinse and pile O/N

percentage grafting (PG) weight of the graft polymer = × 100 weight of the back bone (polymer)

(1)

(2)

Table 3 summarizes the results of percentage of grafting and grafting efficiency of copolymer of different composition. Table 3. Percentage of Grafting and Grafting Efficiency of Cloisite-g-Methacrylic Acid Copolymer

1 2 3 4 5

sample SH SH SH SH SH

20 21 22 23 24

total polymer (g)

wt of graft

percentage grafting (PG)

percentage grafting efficiency (PGE)

5.7 5.2 6.8 7.8 8.4

5.5 4.7 4.9 6.5 6.9

55.0 47.3 49.1 32.7 34.3

96.2 91.1 72.0 83.3 81.9

before neutralization Coralon OT 1% 10′ + dye 3% run for 30′ water 100% at 60 °C + fat liquor 3% 30′ + formic acid 2% 3*5 + 45′ check the exhaustion water 100% dye 2% Run for30′ 2% formic acid 3*5 +45′ rinse and pile O/N

and experimental leathers. A test specimen was conditioned, and the width of each test piece to the nearest 0.1 mm was measured at three places on the grain side and flesh side. The sample was mounted on the jaws. Then, the machine was run at the rate of 100 mm/min until the specimen broke. The procedure was repeated for all other samples. The values were tabulated (see Table 4). Grain Crack Index and Water Vapor Permeability. The lastometer (STD 104, UK) test is intended to determine grain crack force and distension at grain crack. Test specimens of 44.5 mm diameter are cut from the testing area of the leather. Test specimens are conditioned at 20 ± 2 °C and RH 65 ± 2% for 48 h. Then, test pieces were tested on the machine. The values of control and experiment were tabulated (see Table 5). Water vapor permeability (WVP), Croydon-England, test method (SATRA 06121) is to determine the ability of leather to permeate the amount of water vapors (steam vapors) in terms of milligram/unit area and for a specified period of time. During the testing, the samples were tested for 8−16 h. Water vapor permeability was measured for all the sample, and the values are given in Table 6. FTIR Spectroscopic Studies. The FTIR spectrum of homopolymer (Figure 1a, solid line) shows a peak at 1694 cm−1 due to carbonyl stretching vibrations. The bands at 2934, 1449, and 1388 cm−1 were from CH3 vibrations. The surface modified graft copolymers of FTIR spectrum (Figure 1b) show a peak at 3629 cm−1 corresponding to the Al−OH and Mg− OH group on the modified MMT (cloisite). A band of CH2 stretching 2963 cm−1 was due to the organic modifiers. A broad and strong peak between 1017 and 1259 cm−1 was attributed to Si−OH stretching vibration. Figure 1b (dotted line) shows the FTIR spectrum of methacrylic acid grafted cloisite nanoclays.

grafting efficiency (GE) weight of the grafted copolymer = × 100 weight of the total polymer (homo + grafted)

s. no.

after neutralization 2% 30′ Coralon OT 1% 10′ + dye 3% run for 30′ water 100% at 60 °C + fat liquor 3% 30′ + formic acid 2% 3*5 + 45′ check the exhaustion water 100% dye 2% run for 30′ 2% formic acid 3*5 +45′ rinse and pile O/N

Physical Testing of Nanocomposite Retanned Leather. The physical properties of the nanoclay nanocomposite treated leathers were measured by INSTRON 3369, USA. The stress−strain properties of the samples (after neutralization and before neutralization) were tested as per the SATRA(TM-43) physical test methods. All the stress−strain values are given in Table 4. Test pieces of standard shape and size were cut from at parallel and perpendicular directions to the backbone of control 1382



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Table 4. Physical Properties of the Leather tensile strength (MPa)

thickness (mm)

tear strength(MPa)

thickness (mm)

sample code

along

across

along

across

along

across

along

across

control (after neutralization) SH 12 SH 20 SH 21 SH 22 SH 23 SH 24 control (before neutralization) SH 12 SH 20 SH 21 SH 22 SH 23 SH 24

22.12 21.28 25.49 20.74 18.71 24.99 22.78 26.74 27.45 30.45 28.26 25.78 27.07 26.03

17.4 14.75 21.12 15.13 15.16 17.35 20.52 17.64 20.25 23.19 17.74 24.33 20.31 20.04

0.87 1.10 1.18 1.00 0.97 1.01 0.86 0.85 1.11 0.82 0.86 0.95 0.85 0.87

0.93 1.13 1.06 1.04 0.95 0.98 0.90 0.91 1.14 0.91 0.91 0.98 0.91 0.95

33.21 31.37 41.14 44.02 35.65 42.12 35.74 42.86 33.17 47.15 41.14 48.47 39.99 41.38

33.57 43.68 46.67 45.48 40.32 40.45 39.88 46.84 42.35 47.46 43.81 44.48 47.91 42.14

0.86 1.10 1.12 1.06 0.98 1.06 0.9 0.9 1.11 0.81 0.87 0.95 0.89 0.88

0.88 1.03 1.02 1.06 0.9 1.08 0.87 0.89 1.11 0.81 0.87 0.90 0.87 0.88

The decrease in intensity in the region of 3458 and 1694 cm−1 was observed, and a new peak at 1541 cm−1 appeared freshly. Those changes in IR spectra are clear indications of grafting of polymers on nanoclays. Differential Scanning Calorimetry (DSC). Differential scanning calorimetry (DSC) was performed to determine the thermal transition temperatures like glass transition temperature (Tg), melting temperature (Tm), and crystallization temperature (Tc) of the homopolymers as well as copolymers. Figure 2a shows the DSC thermogram of cloisite (SH00), polymethacrylic acid (SH12), and one representative grafted copolymer with nanoclays (SH21). Figure 2b shows the DSC thermogram of grafted copolymers with different weight percentage of nanoclays. The homopolymer (PMA) of the thermogram (Figure 2a) shows a Tg (glass transition) of 66.72 °C. It is obvious that the grafted copolymers with different weight percentage of nanoclays exhibit lower glass transition temperature as compared to homopolymer. Thermogravimetric analysis was performed on homopolymers, nanoclays, and methacrylic acid grafted copolymers. Figure 3a shows the TGA thermogram of cloisite (SH00), polymethacrylic acid (SH12), and one representative grafted copolymer with nanoclays (SH23). Figure 3b shows the TGA thermogram of grafted copolymers with different weight percentages of nanoclays. The thermogram of SH12 shows two stage decompositions, the initial decomposition occurs at 209.3 °C and the final decomposition occurs at 389 °C (see Figure 3a). The TGA thermogram exhibits decrease in decomposition temperatures with incorporation of nanoclay contents in the composite matrix. The composite of methacrylic acid/nanoclays thermogram shows two stage decompositions. This may be due to the low molecular weight of the grafted polymer onto closite 10 Å and less efficiency in grafting. Viscosities of the nanocomposite solutions were determined using Brookfield viscometer with different RPM and spindles. The viscosities of the nanocomposities shows less viscosities compared to homopolymer. For example, the PMA shows the viscosity of 8950 mPa·s. Whereas SH20 4661, SH21 1066, SH22 1070, SH23 448, and SH24 155 mPa·s. The unusual low viscosity of SH24 is possibly the result of low efficiency in polymerization in presence of the cloisites. In this case, the cloisites decreases the rate of polymerization.

Table 5. Lastometer Data for Control and Samples sample code

load (kg)

distension (mm)

33

12.7

41 42 28 31 31 46

11.74 11.51 10.19 13.73 11.00 12.81

control (after neutralization) SH 12 SH20 SH21 SH22 SH23 SH24

sample code

load (kg)

distension (mm)

29

10.41

39 32 34 30 25 29

13.00 10.36 10.87 10.16 8.76 10.28

control (before neutralization) SH12 SH20 SH21 SH22 SH23 SH24

Table 6. Water Vapor Permeability Data for Control and Samples sample code

WVP (mg/(cm2 h))

control SH 12 SH 21 SH 22 SH 23 SH 24

13.44 14.71 14.97 13.55 14.03 14.33

Figure 1. FTIR spectra of (a) homopolymer (SH12)solid lineand (b) PMA-g-cloisite copolymers (with 2% cloisite SH23)dotted line.

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Figure 2. (a) DSC thermograms of cloisite (SH00), polymethacrylic acid (SH12), and one representative grafted copolymers with nanoclays (SH21); (b) DSC thermogram of grafted copolymers with different weight percentage of nanoclays.

Figure 3. (a) TGA thermograms of cloisite (SH00), polymethacrylic acid (SH12), and one representative grafted copolymers with nanoclays (SH23); (b) TGA thermogram of grafted copolymers with different weight percentage of nanoclays.

Figure 4. . Flow curve for (a) PMA and (b) cloisite-g-MA.

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Figure 5. SEM photomicrograph of (a) control sample (AN), (b) SH 12 (AN), and (c) SH 21 (AN).

and weight average molecular weight of the polymer, Mw and polydispersity index, PDI, of the sample SH22 is 38 000, 79 800, and 2.1 as determined by GPC) . The polymers fill the voids in the crust leather and give good tensile strength properties. Grain crack test was measured for all the composite treated leather samples. The SH20 and SH24 show better performance. Water vapor permeability was measured for all the samples and the values are given in Table 6. The nanoclay samples show improved properties with increasing the nanoclay content. This may be due to the porous nature of the clay content. Scanning Electron Microscopy (SEM). The surface morphology of the chrome tanned leather shown in SEM micrographs of cloisite based nanocomposites finished leathers are given in Figure 5a−c. It was observed that the SEM samples retanned by cloisite-g-MA nanocomposites have smooth fiber, firmness, and grain. These are clear evidence for the penetration of the copolymer nanocomposites onto the leathers which have excellent dispersion and filling properties on leather. The filling of the grain layer improve buffability of the leather. We believe that the basis for the tanning mechanism of the cloisite based nanocomposites was the electrochemical interactions of the carboxylic acid groups with the amino groups of the collagen. In this case, the reactivities of active groups of acrylic acid may have been improved in the presence of cloisites. The physical networks have formed between the cloisite based nanocomposites and collagen fibers. It may be a reasonable to expect such a compound to form a coordination complexes with chrome. Transmission Electron Microscopy (TEM). Figure 6 shows the transmission electron microscope image of a representative cloisite graft polymer sample (SH21). Cloisite nanoparticles and polymers are separately visible in the image.

The pH of the nanocomposites solutions were adjusted between from 2 to 3.4 using 40% NaOH solution to apply these solutions as filler with retanning agents on leather. Rheological Properties of the Nanocomposites. Flow behavior of the cloisite-g-MA nanocomposite (SH20, 0.1 wt % cloisite 10 Å) and PMA are given in Figure 4. Figure 4a and b shows the viscosity changes as a function of shear stress for PMA and cloisite nanocomposite. A representative flow curve for SH20 is given in Figure 4b, that shows higher viscosity [85.2 Pa·s] than the neat polymer [27 Pa·s]. The cloisite based nanocomposites show low shear rate (γ, 1/s) than homopolymer PMA, which are the characteristic for the nanocomposites. This may be the ratio between droplet surface and droplet volume and as a consequence, the resulting increase in the interaction between the droplets may leads to higher viscosity. Moreover, all the nanocomposites showed a decrease in viscosity with increase in the shear rate (γ̇). These cloisite-g-MA nanocomposites exhibit a shear-thickening behavior. In general polymers having high molecular weights have a tendency to entangle with neighbor polymer in the three-dimensional network at low shear rate (γ̇). During the shear all the molecules may be oriented in the shear direction by entangling to a certain extent, which may lower their flow behavior. The cloisite clay may be intercalated or delaminated, which could support this orientation by alignment of their rigid crystalline lamellar structure toward the direction of flow at high shear rate as similarly reported by other authors.18 The viscosity of polymer and nanocomposites indicates a similar trend, but clay affects the viscosities. This result indicates that the more organophilic cloisites show better compatibility with the polymer chain, which leads to stronger intermolecular interactions resulting in higher viscosities and stronger shear thickening behavior. The tensile value of the homopolymer treated leather is 21.28 MPa. The values for the methacrylic acid/cloisite nanoclay treated leathers with different weight percentages are given the Table 3. As tabulated in Table 4, SH20 shows higher tensile value of 25.49 MPa compared to other samples. The percentage of clay varied from 0.1−2 wt %, and the tensile value increased for SH20 and SH24. The SH20 has low weight percentage of the composites (0.1% clay) and has better interaction with collagen. Increasing the clay content, the interaction between nanoclays and collagen did not improve much. So the lower nanoclay incorporated graft copolymer may be the best compositions for the leather as filling with retanning agents. Similarly the Table 4 shows tear strength value increases with increasing the clay content. It was observed that SH22 has broad molecular weight distributions and low molecular weight in nature (the number average molecular weight, Mn 38 000,

Figure 6. TEM image of the sample SH 21. The scale bar is 0.5 μm. 1385



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CONCLUSION Grafting of cloisite-g-methacrylic acid copolymers on to nanoclay with different weight percentage was successfully demonstrated. All the graft copolymers were characterized by using FTIR, DSC, TGA, and viscosities. All the grafted nonpcomposites exhibit shear thickening non- Newtonian flow behavior. The characterized copolymers were applied on the cluster leather as filler with retanning agent. The retanned leathers were tested by their physical properties. The lower weight percentage nanoclay incorporated methacrylic acid graft copolymers nanocomposite exhibits the best threshold ratios for the crust leather as retanning agents. The initial addition of the cloisite in the polymerization reactions shows decreased viscosity with increasing the weight percentage of the clays.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +91-44-24422059. Fax:+91-44-24911589. E-mail: [email protected] or [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS S.N.J. is thankful to Mr. R. Radhakrishnan for leather coating at Clariant Chemicals (India) Ltd. Chennai India, and Mr. V. Srinivasan and Mr. Pramod Ragunanthan for the rheological studies at Anton Paar, India. The authors acknowledge the partial funding from CSIR cross cluster project ZERIS.

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(29) Ma, J. Z.; Chen, J.; Chu, Y.; Yang, Z. S. The preparation and application of a montmorillonite based nanocomposite in leather making. J. Soc. Leather Technol. Chem. 2002, 87, 131−134.

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Cloisite-g-Methacrylic Acid Copolymer Nanocomposites by Graft from

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