Maleic Anhydride Grafted Atactic Polypropylene As Exciting New

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Maleic anhydride grafted atactic polypropylene as exciting new compatibilizer for poly (ethylene-co-octene)-organically modified clay nanocomposites: Investigations on mechanical and rheological properties Anirban Bhattacharya, Soumya Mondal, and Abhijit Bandyopadhyay Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie400649p • Publication Date (Web): 10 Sep 2013 Downloaded from http://pubs.acs.org on September 17, 2013

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Industrial & Engineering Chemistry Research

Maleic anhydride grafted atactic polypropylene as exciting new compatibilizer for poly (ethylene-co-octene)-organically modified clay nanocomposites: Investigations on mechanical and rheological properties

Anirban Bhattacharya, Soumya Mondal and Abhijit Bandyopadhyay* Department of Polymer Science and Technology, University of Calcutta 92, A.P.C. Road, Calcutta- 700009, India *Corresponding Author: Tel: +91-033-235013976996/6387/8386, Extn: 288 Email: [email protected]

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Abstract This is probably the first report on maleic anhydride (MA) grafted atactic polypropylene (aPP) acting as typical compatibilizer for synthesis of poly (ethylene-co-octene) (POE)organically modified montmorillonite (OMMT) nanocomposites. The maximally grafted aPP (93.67% with 3 wt% MA) was used for compatibilization. OMMT concentrations were varied as 1, 3 and 5 wt% with respect to POE. Only moderate improvements in mechanical and rheological properties were recorded in both uncompatibilized (POE-OMMT) and compatibilized (POE-OMMT-1 wt% compatibilizer) nanocomposites due to predominant aggregation of OMMT layers. However, at higher compatibilizer content e.g. 3 and 5 wt%, similar properties were hugely improved (92% rise in tensile strength, 55% rise in net elongation etc.) due to partial de-lamination of OMMT galleries. Better processibility including reduced die swell and flow activation energy and smoother extrudate profiles were also obtained as additional benefits at those compositions due to orientation of the delaminated OMMT layers in the flow direction.

Key words: atactic polypropylene, poly (ethylene-co-octene), nanoclay, compatibilizer, mechanical, processibility

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Introduction Metallocene-based poly (ethylene-co-octene) (POE) and poly (ethylene-co-butene) (PBE) are excellent new generation thermoplastic elastomers (TPE). They have uniform co-monomer contents and narrow molecular weight distribution1 which results into interesting combination between their tensile strength and toughness. However, presence of limited short chain branches (octene and butane) hinders quick stress dissipation and produce melt fracture defects, which is considered as their major limitation2. POE is slightly more popular than PBE due to marginally better processibility. It has different grades available in the market. Gradation is done based on its octene content and percent crystallinity. Some previous investigations on POE show that the general purpose grade has been effectively applied as a toughening agent in many thermoplastics like polypropylene (PP)3,4, polyesters5,6 and nylon7,8. Recently, Rajeshbabu et. al. have synthesised radiation crosslinked PP-POE blends using similar grade for better physico-mechanicals9. POE, in addition, had also prevented the degradation of PP. References on direct acid grafting on POE using acrylic acid10,11, maleic anhydride12, benzene sulphonic acid13 etc. to modify its physico-mechanicals are also abundant. Our group previously had reported the melt-induced interpenetrating network (IPN) synthesis in POE using various polar polymers like ethyleneco-acrylic acid (EAA) and ethylene-co-vinyl acetate (EVA) for its improved mechanical and solvent resistance properties14,15. Property enhancement using modified montmorillonite in nylon 6 was first demonstrated by the Toyota Research Group in 199316. They reported a net 69% rise in tensile modulus, 42% rise in ultimate tensile strength, 62% rise in flexural strength and 134% rise in heat deflection temperature of nylon 6 in presence of 4 wt% modified montmorillonite. Since then, many synthetic and natural polymer based nanocomposites including different polyolefins have been synthesised and investigated unveiling several promising properties. Few such examples are: 130% improvement in tensile strength of natural rubber17, 20% improvement in fracture toughness of high density polyethylene (HDPE)18 and 300% rise in gas barrier resistance of polyurethane (PU)19 at optimum nanofiller loading. But, strangely, only one study on POE-electron beam modified montmorillonite nanocomposite has been reported so far by Ray and Bhowmick20 in 2002 or else, this area has remained utterly unexplored. Sodium montmorillonite is the most widely investigated nanofiller so far. It has high cation exchange capacity through which the sodium ions are exchanged with giant ammonium ions to produce organically modified montmorllonite (OMMT). It is a simple technology and is easily performed in the laboratory scale. However, OMMT is also 3



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commercially available. The commercial grades may have a mixture of different high molecular weight amines instead of a single one, intercalated between the clay galleries. Some important polyolefin-OMMT composites investigated so far includes: HDPEOMMT18, LDPE-OMMT21 and PP-OMMT22. Often, compatibilizers are used to facilitate OMMT dispersion, for example, use of styrene-ethylene-co-butylene-styrene (SEBS)-gmaleic anhydride in the preparation of nylon6/PP/clay nanocomposites23. Recently, aPP has attracted huge research interest. It has been explored as a compatibilizer in formation of PP/talc composites24 and as an independent matrix for nanocomposite synthesis with OMMT25. aPP is an industrial waste with its annual production now reaching nearly 22.5% of the whole PP amount26. It is extremely soft and waxy. The only commercial use known so far is as hot melt adhesive. Use of grafted polyolefins as efficient compatibilizers for synthesis of polyolefin/OMMT nanocomposites has been well described in the literature27-31. Maleic anhydride (MA), succinic anhydride etc. were successfully used as grafting agents. The main reason for choosing modified polyolefins for compatibilization was to accomplish better technical compatibility with the matrix. But high compatibility leading to better phase mixing often reduced polyolefin crystallinity and lowered the composite strength. Thus, a low crystalline matrix like polyolefin based TPE instead of a highly crystalline polyolefin could be a better alternative as it can avoid the adverse effects resulting out of huge crystallinity drop during compatibilization. Conceding that we have investigated POE based hybrid nanocomposites, which, incidentally has also been the least explored area in the similar category. MA grafted aPP (aPP-g-MA) was used as the compatibilizer for the nanocomposite synthesis. MA grafting on isotactic PP (iPP) is well documented32,33 and thus grafting on aPP does not add any novelty to this investigation since both aPP and iPP have identical microstructures. However, its role as a compatibilizer in nanocomposite synthesis is yet to be studied and thus is an area of high interest in this investigation. Experimental Materials: General purpose poly (ethylene-co-octene) (POE), commercial grade EngageR 8200 with high octene percentage, was procured from DuPont Dow Chemical Corporation (now Dow Chemical Company), Wilmington, DE. It was used as the base elastomer for current investigation. It has 21% overall crystallinity, density 0.87, DSC melting point of 590 C, hardness 63 Shore A and DSC Tg of -530 C. The nanoclay used was methyl dihydroxyethyl hydrogenated tallow amine modified montmorillonite (OMMT) purchased from Sigma4


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Aldrich, USA. Extremely soft and waxy atactic polypropylene (aPP) with theoretical softening point 1350 C was generously supplied by Reliance Industries Ltd., Mumbai, India. Maelic anhydride and benzoyl peroxide (grafting initiator), each of 99.5% purity, was purchased from Loba Chem, Mumbai, India and were used without any further purification. aPP based compatibilizer preparation aPP along with 1, 3, 5, 7 and 10 wt% MA and 1 wt% benzoyl peroxide (all with respect to aPP) were taken to accomplish the grafting reaction. Benzoyl peroxide was used as grafting promoter. The reactions took place in a Brabender Plasticorder (TYP 815606, Germany) at 650 C under 60 rpm mixing speed. The mixing temperature was kept low in order to generate adequate shearing. The batch weight was 40 g. aPP was first pre-heated for 1 min, then MA was added and mixed for another 1 min and finally, benzoyl peroxide was added and the whole mass was mixed for another 2 min. The final mixing time was optimized from the torque-time monitoring curve. POE-OMMT nanocomposite synthesis POE granules were preheated in the same Brabender mixer at 180⁰C for 1 min. Compatibilizer was added in various proportions and mixed for another 1 min. Finally, OMMT was added in prescribed weight proportions and the whole mass was mixed for another 2 min. Uncompatibilized blends were prepared by mixing OMMT for 2 min directly after 1 min preheating. Similarly, blank compositions without nanoclay were prepared by mixing aPP-gMA with POE for 1 min. Particulars about all blend compositions are reported in Table 1. The samples taken out of the hot mixer were immediately cut into small pieces, cooled and finally molded in a hydraulic press at 1800 C for 5 min under 5 MPa pressure. Characterization Determination of grafting efficiency About 2 g of the sample, wrapped in filter paper, was put into toluene and was extracted overnight. The wrapped residue was unwrapped, dried in an oven to remove absorbed toluene and then again wrapped and boiled in water for 15 min to remove all unreacted maleic anhydride. The boiling was restricted to 15 min to avoid hydrolysis of the anhydride units. Finally, the residual mass was weighed to calculate the grafting efficiency using Equation 1: 5



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Grafting efficiency (% ) = [(Pure aPP weight + MA added) – (Final weight after removal of unreactive MA)/ (Pure aPP + MA added)] x 100

(1)

Infrared spectroscopic analysis Fourier Transform infrared (FTIR) spectroscopic analyses of the grafted samples were carried out in a FTIR spectrophotometer (Spectrum GX) purchased from Perkin–Elmer Ltd., England. The machine was equipped with a DTGS detector. IR spectra were recorded within 4000–400 cm-1. Each spectrum was an average of 120 scans having peak resolutions of 4 cm1

. A programmable temperature controller (Model 50–886, Love Control Corporation) was

used for each scan to perform the thermal perturbation.

Mechanical properties analysis The test specimens were die punched from the sample sheets into dumbbells for evaluation of the mechanical properties. Tensile modulus, ultimate tensile strength and net elongation were tested as per ASTM D-412 in a Universal Testing Machine (UTM LLOYD instrument LR 10 K plus Load Cell 10 KN) at room temperature. An average of three test results is reported for analysis. Scanning Electron Microscopy High resolution imaging of the nanocomposite surfaces was carried out using a scanning electron microscope (SEM) purchased from JEOL (JEOL JSM 5800). The fresh surfaces were exposed by cutting each sample surface with a new knife. They were subsequently gold coated to avoid artifacts generation due to beam heating. The imaging was done at a voltage of 20 KV. Transmission Electron Microscopy The nanostructure of OMMT was visualized under a transmission electron microscope (TEM, C-16, Philips) operated at 400 KV. The sample was cryo-micotomed and placed over a copper grid of 300 mesh. It was then inserted into the machine for observation. X-ray diffraction analysis

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Wide angle X-ray diffraction studies of the samples were carried out in a X’pert PRO MRD X-ray diffractometer (PANalytical, The Netherlands) within the angle 1 to 400. The crystallite plane distances were calculated using Bragg’s Equation (Equation 2) . 2dsinθ = nλ

(2)

Where, λ is the wavelength of the X-ray (0.154 nm, source CuKα), θ is the scattering angle, n is an integer representing the order of the diffraction peak and d is the inter-planar distance. The crystal lamella thickness was determined by the Scherrer Equation (Equation 3)

τ = κ λ / βcosθ

(3)

Where, τ is the crystallite thickness, κ is a shape factor ( typical value = 0.9), λ is the X- ray wave-length, β is the line broadening at half the maximum intensity in radian ( FWHM ) and θ is the Bragg’s angle. Analysis of stress relaxation The tensile specimens were extended to 100% at a speed of 50 mm/min in the tensile tester mentioned earlier and held constant at that point until the decaying stress reached equilibrium following Equation 4. S = S0e (-t/ λ)

(4)

ln S = ln S0 – t/ λ

(5)

Where, S is the decaying stress at different time t and S0 is the stress at zero time i.e. the stress at 100% elongation. λ is the relaxation time. The decaying stress with time was recorded manually and fitted to Equation 5. The relaxation time was calculated from the slope of the plot of ln S vs. t.

Analysis of hysteresis loss Hysteresis test was performed by extending the tensile specimens to 100% at a speed of 50 mm/min and then subsequently allowing them to return to zero extension for three consecutive cycles. The experiments were carried out at room temperature using same tensile

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tester. The loop area, equivalent to hysteresis loss, is reported as the numerical average of three consecutive cycles.

Melt Flow Index (MFI) study MFI of the samples was measured by weighing the mass output in 10 min at 190°C through a standard die of 2.0955 ± 0.0051 mm diameter and 8.000 ± 0.025 mm length under a fixed load of 2.16 Kg. Activation energy for flow was determined by repeating the experiment at 200 and 2100 C. Logarithm of the mass ejected at each temperature was plotted against inverse of the temperature and the energy was calculated from the slope of the best fit straight line.

Die swell measurement and extrudate profile analysis The die swell of the extrudates in percent were calculated using Equation 6.

Die Swell (%) = [(Diameter of the extrudate)/ Die diameter)] x 100

(6)

The diameters of the extrudates coming out of the MFI instrument were measured using a digital slide calipers. Ten readings were taken within 1 inch extrudate length, averaged and was reported as the extrudate diameter in each case. Extrudate profiles were analyzed visually from the magnified images taken by a digital camera.

Results and discussion Optimization of MA grafting on aPP in melt The probable chemical reactions involving aPP, MA and benzoyl peroxide are demonstrated in Scheme 1. The process initiates either by combination of the initiator radicals with MA (reaction A) leading to dismutation (reaction A) or by induction of macroradicals over aPP molecules. The former eventually proceeds towards a dead end while the latter activates series of reactions. The macroradicals can simultaneously undergo self-combination (rise in molecular weight, reactions C and E), β scission (drop in molecular weight, reactions D and H) and grafting reactions with MA molecules (reactions F and G and reactions H, J and K). The reaction sub-chain F and G shows MA grafting on undegraded aPP molecules whereas 8


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the sub-chain H, J and K demonstrates grafting preceded by the β scission. However, another possibility could be MA grafting followed by β scission shown through the sub-chain L, which produces two probable microstructures, 7 and 8. Finally all relevant products would undergo dismutation through hydrogen transfer. The FTIR spectrums of all reacted aPP samples are shown in Figure 1. Absorbance at 2868 and 2962 cm-1 marked the presence of aliphatic C-H stretches of aPP molecules. The complementary bending peaks of both CH2 and CH3 units appeared at 1455 and 1376 cm-1. The absorbance at 1740 cm-1 denoted the C=O stretching frequency of the grafted MA units. It eventually represented all grafted microstructures shown by 4, 6, 7 and 8 in Scheme 1 since they were physically indistinguishable. A weaker absorbance at nearly similar position was also noticed with virgin aPP. It was possibly due to minor oxidation effect at its labile tertiary hydrogen on the backbone chain. The gravimetric grafting yields calculated against different MA concentrations are reported in Table 2. All values are on the higher side and are rationally close. It evidently shows high grafting probabilities at all MA concentrations. But still, the maximum (93.67%) was achieved at 3 wt% since at higher compositions, reaction A probably became more competitive and reduced the grafting efficiency.

Studies on POE-OMMT nanocomposites All nanocomposites were prepared using 3 wt% MA grafted aPP (aPP-g-MA3). Both aPP-gMA3 and OMMT concentrations were varied for optimization. Blank experiments with aPPg-MA3 were also carried out to investigate its sole effect on POE. The tensile behaviors of the composites are demonstrated in Figures 2a-c. Their wide angle X-ray diffractograms are shown in Figures 3a-d. Neat POE had shown a tensile strength of 4.25 MPa (Figure 2a and Table 1). Its diffractogram exhibited two mutually interfering peaks located at 20.43 and 22.0 degrees34. Those peaks were de-convoluted and are shown in the inset. The net crystallinity and crystallite thickness were calculated from the de-convoluted profiles. The values are reported in Table 3. Addition of 1 wt% OMMT in POE (POE1) had slightly increased the composite strength to 4.82 MPa but the modulus marginally dropped from 2.16 to 1.99 MPa. However, the net elongation significantly increased from 1528.2% to 1952.9% (Figure 2a and Table 1). The diffraction data showed marginal rise in net crystallinity (21.41 to 21.62%) in POE1 which was supposed to be responsible for improvement in tensile strength. Higher elongation was, however, due to better heat 9



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dissipation characteristics impressed by the presence of thinner lamella of the POE molecules (Table 3). But with 3 wt% OMMT (POE3), both tensile strength and elongation did not improve as much as POE1 (Figure 2a and Table 1). We assume that to be due to rise in lamellar thickness distressing heat dissipation behavior of the composite. Also poor matrixOMMT interaction emanating from its poor dispersion status (indicated by the identical diffraction angle and gallery spacing as that of the virgin, Figure 3b and Table S1 (shown as Supporting Information) was also responsible as well. The composite surface appeared to be extremely wavy and showed presence of thicker OMMT stacks of average thickness exceeding 1.5 µm (the SEM image of POE3 shown as inset in Figure 3a). However, addition of 5 wt% OMMT (POE5) had drastically improved both tensile strength and elongation but the modulus dropped marginally from its preceding value (Figure 2a and Table 1). Higher crystallinity along with reduced lamellar thickness was primarily responsible for that (Table 3) since interaction with OMMT was even poorer than POE3 due to greater aggregation effect (indicated by the positive shift in diffraction angle in Figure 3b and Table S1 (shown as Supporting Information) which is equivalent to reduced inter-planner distance). But in spite of that, the mechanical properties were much improved than neat. Unlike POE5 similar improvements in POE1 and POE3 was poor and thus were selected for further investigation with aPP-g-MA3 to study its compatibilization efficacy. But, before moving into that, the sole effect of aPP-g-MA3 on mechanical and other properties of POE was investigated. Tensile properties of blank samples containing 1 (POEC1), 3 (POEC3) and 5 (POEC5) wt% aPP-g-MA3 are reported in Table 1. It shows that, except net elongation, both tensile modulus and strength steadily declined on raising the aPPg-MA3 content. The net elongation, however, had shown the reverse trend. Both tensile strength and modulus were reduced due to intimate mixing between POE and aPP-g-MA3 owing to identical backbone structures. Moreover, drop in net crystallinity was also responsible as well (Table 3). Higher elongation was registered due to formation of thinner lamella than neat POE. Nevertheless, in the nanocomposite series, both POE1/1 and POE3/1 had produced lower tensile strength, modulus and net elongation than POE1 and POE3 (Figure 2b and c and Table 1). Despite higher crystallinity (except POE3/1 where the net crystallinity was marginally low) and low lamellar thickness, their poor mechanical properties were likely to be due to improper OMMT dispersion. Conversely, the properties drastically improved in presence of 3 and 5 wt% aPP-g-MA3. Both POE1/3 and POE3/3 had exhibited radically improved tensile 10


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strength and elongation than POE1 and POE3. In POE1/5 the tensile strength seemed to be saturated but a steep rise of 1.2 MPa was still achieved with POE3/5. Tensile modulus and elongation were also improved significantly. Superior tensile strength of POE1/3 and POE1/5 over POE1/1 and POE1 was due to partial de-lamination of OMMT platelets aided by the presence of higher aPP-g-MA3 concentration since contribution from net crystallinity was insignificant (Table 3). The de-lamination was probably more effective in POE1/5 since higher POE-OMMT interaction had raised the tensile modulus from 2.09 to 2.44 MPa. Higher extensibility was achieved due to efficient heat dissipation by the thinner lamella of the compatibilized samples. POE3/3 had shown equivalent tensile modulus and strength as POE1/3 but its net elongation was higher than POE1/3 due to low lamellar thickness. POE3/5 had exhibited remarkable improvements in mechanical properties due to mutual contributions from i) higher de-lamination effect of OMMT platelets and ii) significant rise in net crystallinity. Low angle diffractogram in Figure 3b and the diffraction data in Table S1 (as Supporting Information) clearly showed widening of the inter-gallery space of OMMT in presence of 5 parts of aPP-g-MA3 which is equivalent to partial de-lamination of OMMT galleries. Finer platelets than before in POE3/5 eventually acted as nucleating agent for POE and raised its net crystallinity from 21.41 to 30.90%. Higher de-lamination had created more POE-OMMT interaction and further raised the modulus from 2.10 to 2.82 MPa. The relevant SEM images are shown in Figures 4a-c. Greatly improved surface morphology with less undulations and finer clay dispersion was observed in POE3/1 (Figure 4a) as compared to POE3. Average OMMT thickness drastically reduced from 1.6 µm to 75 nm owing to reduced energy difference between POE and OMMT through compatibilization. Increasing compatibilizer concentration had produced even better phase mixing in POE3/3 and POE3/5 (Figures 4b and 4c). The surfaces appeared even smoother and the average length and thickness of the OMMT stacks were further reduced. The stacks were more POE coated and thus did not appear as brighter as the preceding compositions. Average platelet thickness was reduced to 63 nm in POE3/3 (Figure 4b) and 40 nm in POE3/5 (Figure 4c). Excellent OMMT dispersion in POE3/5 was further delineated through TEM imaging in Figure 4d. Uniformly dispersed and virtually oriented OMMT platelets with average thickness 42 nm were seen to be embedded within POE. Excellent corroboration between average platelet thickness from TEM and SEM (40 nm, Figure 4c) factually proved supreme uniformity in OMMT dispersion both inside the bulk and at the surface positions in presence of high aPP-g-MA3 concentrations. 11



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High aPP-g-MA3 concentration was thus the necessity to achieve better mechanicals. Scheme 2 entails the probable reason. The OMMT platelets were positively charged (zeta potential +3.43 mV) due to adsorption of organic ammonium ions both at the OMMT surface and inside of the inter-gallery spacing. The bound moisture associated with positively charged OMMT explicitly hydrolyzed the anhydride units of MA into COOH (Step I). Those COOH moieties subsequently interacted with the adsorbed ammonium ions and moved closer to the OMMT surfaces along with the intimately mixed POE segments (Step II). Since more COOH units (i.e. high aPP-g-MA3 concentrations) favoured more POE segments to migrate closer to the OMMT surface, the higher pressure exerted by the segments on the OMMT aggregates eventually de-laminated few OMMT galleries. Few POE segments from its very high population around OMMT could also move into the clay galleries and execute the same. At low aPP-g-MA3 content, insufficient POE population around OMMT could not generate enough pressure for de-lamination and thus the property improvements were low at low aPPg-MA3 concentrations. The dynamic properties like stress relaxation and hysteresis were also remarkably affected by the variant clay morphology (Table 1). The relaxation profiles of the nanocomposites shown in Figure 5 do not include profiles of neat POE and the blank samples to avoid overcrowding. Table 1 shows that, the relaxation time of POE was immediately reduced on OMMT addition (POE1) but then slowly picked up at higher OMMT contents (POE3 and POE5), although it had never exceeded the relaxation time of the neat POE. Uncompatibilized nanocomposites had more aggregated morphology leading to poor POE-OMMT interaction. The low and close hysteresis loss due to presence of more free and elastic segments (unadsorbed) is possibly another evidence of that. Poor POE-OMMT interaction followed by low POE volume fraction had reduced the relaxation time of all uncompatibilized composites than neat POE. The blank samples had shown faster relaxation than neat as well but it was due to different reason (Table 1). Waxy aPP-g-MA3 produced excellent phase mixing with POE and improved heat dissipation behavior (higher elongation and lower hysteresis). Presence of such flexible segments induced faster relaxation which constantly became faster on more aPP-g-MA3 addition (3 and 5 wt%) in POE. Conversely, the relaxation time tremendously increased in the compatibilized nanocomposites, particularly in POE3/3 and POE3/5 due to formation of more “slow relaxing” domains. More de-laminated clay morphology (Scheme 2) particularly at higher aPP-g-MA3 levels had enhanced POE-OMMT contacts which remarkably arrested the segmental fluidity of POE and retarded the relaxation behavior. Such 12


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segmental immobility was further complemented with huge hysteresis loss which is noted in Table 1. Neat POE had shown high flow ability which strongly perturbed on OMMT addition in uncompatibilized system. In fact, the flow gradually reduced with increasing OMMT content since more aggregated morphology created more hindrance in polymer flow (Table S2, shown as Supporting Information). But the activation energy had slightly reduced than virgin due to faster sliding of the mass over thick aggregated layers owing to loss of interaction at elevated temperatures. Figure 6 compared the visuals of selective extrudate profiles. Neat POE showed severely deformed texture due to high residual stress (low hysteresis loss). The die swell was also high, 63%, due to faster relaxation (Table 1). Conversely, extrudates of POE1, POE3 and POE5 were comparatively less deformed (only POE3 has been shown) as the inorganic OMMT had slightly improved stress dissipation behavior. However, the die swell was reduced (51%) despite faster relaxation, due to slightly more lossy nature of the composites (higher hysteresis loss) than neat. Conversely, all blank samples had exhibited improved flow rate and reduced activation energy due to softening of the mass by the presence of aPP-g-MA3 (Table S2, shown as Supporting Information). However, the extrudate profiles were still deformed alike uncompatibilized system. The die swell was also higher than neat (Table 1) and those were due to their faster relaxation behavior. Conversely, the flow rate was notably improved than blank in the compatibilized nanocomposites. At equal OMMT content, the mass flow rate was higher in presence of 1 parts aPP-g-MA3 which further increased with 3 parts aPP-g-MA3 and then finally saturated at 5 parts aPP-g-MA3. Activation energy followed similar trend (Table S2, shown as Supporting Information). Higher aPP-g-MA3 content had influenced more de-lamination whereby thinner OMMT layers further oriented themselves in the flow direction and assisted more POE segments to slide past. Tensile properties of the extrudates were measured to ensure the orientation theory. Table S2 (shown as Supporting Information) shows the data. Tensile strength of neat POE extrudate was 13 MPa and those of POE1, POE3 and POE5 were restricted within 15 MPa which shows lack of orientability of thicker aggregated mass. With 1 part aPP-g-MA3, the strength was not too great either. But it increased dramatically to the range of 30 MPa in 3 and 5 parts aPP-g-MA3 compatibilized nanocomposites owing to orientation of thinner OMMT platelets along the flow direction. In tandem they showed much less deformed extrudate profiles (Figure 6d) and reduced die swell (32% in POE3/3 and 22% in POE3/5) due to presence of more lossy and slow relaxing segments. 13



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Conclusion The study revealed outstanding role of the new compatibilizer developed from aPP in improving the mechano-rheological features of POE-OMMT composites. The compatibilizer was found to be more effective at 3 and 5 wt% as compared to 1 wt% loading with respect to neat POE. The net rise in tensile strength was 92%, modulus was 30.5%, elongation was 55% and the breaking energy (area under the stress-strain curve) was 155%. The extrudates were smoother and were dimensionally more stable. The flow activation energy was also less indicating better process economy. The trick was partial de-lamination of OMMT galleries induced by high aPP-g-MA3 contents at high OMMT levels. Those wonderful property combinations aspires more future investigations on effectiveness of this unique compatibilizer in similar polymer matrices. Acknowledgement: The corresponding author gratefully acknowledges the financial assistance provided by All India Council for Technical Education, Govt. of India, under the scheme of Career Award for Young Teachers (CAYT) (Ref: 1-51/RID/CA/21/2009-10, June 01, 2010). Supporting Information Available: This information is available free of charge via the internet at http://pubs.acs.org.

14


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Page 19 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. Sample composition, designation and their mechano-rheological properties

Notations

POE

POE1

POE3

POE5

POEC1

POE1/1

POE3/1

POEC3

POE1/3

POE3/3

POEC5

POE1/5

POE3/5

POE (gm)

35

34.65

33.98

33.33

34.65

34.314

34.654

33.98

33.654

33.019

33.33

33.019

32.408

Clay (%)

0

1

3

5

0

1

3

0

1

3

0

1

3

Compatibilizer

0

0

0

0

1

1

1

3

3

3

5

5

5

Initiator (%)

0

0

0

0

1

1

1

1

1

1

1

1

1

Temperature

180

180

180

180

180

180

180

180

180

180

180

180

180

2

3

3

3

2

4

4

2

4

4

2

4

4

2.16

1.99

2.10

2.02

1.90

2.09

2.07

1.65

1.88

1.90

1.32

2.44

2.82

4.25

4.82

4.53

5.83

4.20

4.58

4.43

3.92

7.01

6.96

3.82

7.00

8.15

Net Elongation

1528.

1952.9

1736.9

2438.4

1665.0

1609.8

1660.5

1900

2256.0

>2331.2

>2367.4

(%)

2

Relaxation

26.84

13.12

16.28

20.72

18.67

29.62

56.87

19.3

19.3

21.7

22.8

190.6

224.0

63

59

51

50

37

22

(%)

(0C) Batch Time (Min) Tensile Modulus (@300%, MPa) Tensile Strength (MPa)

21.56

27.55

36.09

144.6

177.6

57

51

19.23

>2292.

>2502.

1

2

28.63

47.07

183.0

193.8

45

32

Time (min) Hysteresis Loop Area (MPa) Die Swell (%)

67

69

19


68


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 2. Gravimetric grafting efficiency

MA in Initial wt%

Final

Residue

weight weight weight (gm)

(gm)

(%)

1

2.160

1.866

86.39

3

2.149

2.013

93.67

5

2.034

1.818

89.38

7

2.119

1.903

89.81

10

2.062

1.725

83.66

Table 3. Wide angle (2θ= 10-400) XRD data Sample

Bragg’s

%

FWHM

Angle

Crystallinity

Crystallite Thickness

(2θ)

(nm)

POE

21.983

21.41

3.867

0.365

POE1

21.719

21.62

3.979

0.354

POE3

22.049

32.72

3.601

0.392

POE5

21.950

25.12

7.029

0.265

POEC1

21.982

21.33

5.089

0.313

POE1/1

21.765

24.55

4.448

0.317

POE3/1

21.765

20.17

4.139

0.341

POEC3

21.675

20.32

5.350

0.298

POE1/3

22.293

18.04

4.321

0.327

POE3/3

22.359

21.19

3.376

0.319

POEC5

21.765

19.98

5.678

0.278

POE1/5

22.029

23.18

4.292

0.329

POE3/5

22.062

30.90

4.026

0.351

20


Page 20 of 33

Page 21 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


OR

O

O O

(1) B

.

OR

O

O O O

A O

O

.

RO

D

C

.

. O

E

F

O

beta scission

H

O O O

. .

O

+ O

J O

(3)

(2) G

beta scission

L

O O

dismutation

O

.

O

.

O O

O

(5)

O O

(4)

O O

O

dismutation

O

O O

or

(7)

K

O

(6)

(8)

Scheme 1: Proposed chemical reactions in melt between aPP and MA in presence of benzoyl peroxide

21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 33

O O

O

H

H

+

O

OH

OH

O

O

Step-1: Hydrolysis of grafted anhydride linkage into carboxylic acid

H

H O

+ O

+ O

+ O

+ O

O

O

O O+

+O

O+

O+

H

H O

O

O HO

H

+ O

O

indicates organic ammonium ion

O

O H O

O +

O

OH + O

+ O

indicates POE segments

+ O

O

OH +O

O

O+

O+

O+

O O

OH

OH

OH

O

O +O +O +O

H

H O

O+ O+ O+

O

O

O

O+

Step-2: Subsequent interaction of the hydrolyzed app-g-MA3 with the adsorbed organic ammonium ion on MMT surface, migration of the app-g-MA3 and POE segments closer to OMMT stacks and finally partial delamination of the OMMT platelet under tremendous pressure of POE segments.

Scheme 2: Mechanism showing partial de lamination of OMMT through interaction with app-gMA3

22


Page 23 of 33

7

2962 cm-1 2868 cm-1

1458 cm-1

6

1377 cm-1

5

% Absorbance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1740 cm-1

10% MAH 7% MAH

4

5% MAH

3 3% MAH

2 1

1% MAH APP Pure

0 500

1000

1500

2000

Wavenumber ( cm

2500

-1

3000

)

Figure 1. FTIR spectra of different MA-g-aPP samples

23



6

POE 5 5

POE 3 PO E 1

4

POE

3

2

1

0 0

500

1000

1500

2000

2500

% Strain

Figure 2a. Tensile data for uncompatibilized POE/ nanoclay systems; the inset shows the SEM image of POE3

8

POE 1/3

7

**

6 5

Stress(MPa)

Stress(MPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

POE 1/5

4 3

POE POE 1/1

POE 1

2 1 0 0

500

1000

1500

2000

2500

% Strain

Figure 2b. Tensile data for POE/1 part nanoclay and compatibilizer variation 24


Page 24 of 33

Page 25 of 33

POE 3/5

8

* *

POE 3/3

*

6

Stress(MPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


POE 3/3 POE 3/1 4

POE

POE 3

2

0 0

500

1000

1500

2000

2500

% Strain

Figure 2c. Tensile data for POE/ 3 parts nanoclay and compatibilizer variation

25



1300 POE/1

21.82

20.41

1200

1200

1100

800

POE/5 POE/3 POE

POE1

22.16

900

20.46

1000

Counts

1000

1100

700

900

Counts

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 33

19.5

20.0

20.5

21.0

21.5

22.0

22.5

23.0

2θ

800

POE5

700

POE3

600 500

POE

400 300 200 100 10

15

20

25

30

35

40

2θ

Figure 3a. XRD spectra and net tensile property variation of POE/clay nanocomposites

26


Page 27 of 33

5000

1200

4.65

4.65 4.75

POE5

4.25

4000

POE3/5

Counts

1000

Counts

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3000

POE3 800

2000

600 1000

400

0

2

4

6

8

3

10

4

5

6

2θ

2θ

Figure 3b. Low angle XRD spectrum of neat OMMT and in different composites

27


7


8000 7000

21.82 22.04 22.14

20.23 20.27

6000

POE/1/1 POE/1/5 POE/1/3

20.45

21.76

1200 1100

5000

Counts

3000

2000

6000

1000

POE1/1

4000

POE1/5

POE/1 POE

1000

900

Counts

7000

POE/1 22.00

800 700

POE

600 19.5

20.0

20.5

21.0

21.5

22.0

22.5

23.0

POE1/3

23.5

2θ

500 20

5000

21

22

23

24

2θ

Counts

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 33

4000

POE1 3000

POE 2000

1000

0

10

15

20

25

30

35

40

2θ

Figure 3c. XRD spectra and net tensile property variation of POE/ 1%clay at different compatibilizer concentrations

28


Page 29 of 33

8000 7000

7000

21.80

20.28

POE/3/1

6000

POE/3/5 5000

20.08

Counts

20.56

6000

POE3/1

4000

3000

22.17 20.73

POE/3/3

2000

20

5000

Counts

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2θ

POE3/5 4000

POE3

3000

POE3/3 POE

2000 1000 0 10

15

20

25

30

35

40

2θ

Figure 3d. XRD spectra and net tensile property variation of POE/ 3%clay at different compatibilizer concentrations

29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

(b)

(c)

Figure 4. SEM images of (a) POE3/1 (b) POE3/3 and (c) POE3/5.

30


Page 30 of 33

Page 31 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100 nm

Figure 4d. TEM image of POE3/5

31



14 13 12

POE POE1

11 10

POE3 POE5

9

Stress (MPa)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 33

8

POE1/1 POE1/3

7 6 5

POE1/3 POE3/3

4 3

POE1/5 POE3/5

2 1 0 0

100

200

300

400

500

600

Time (s)

Figure 5. Stress relaxation behaviors of all nanocomposites

32


Page 33 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 (c) 55 56 57 58 59 60


(a)

(b)

(d)

(c)

Figure 6. Melt extrudate profiles of (a) neat POE (b) POE3 (c) POEC3 and (d) POE3/5

33


Maleic Anhydride Grafted Atactic Polypropylene As Exciting New

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