Environmentally friendly polymer hybrids Part I Mechanical, thermal, and barrier properties of thermoplastic starch/clay nanocomposites

As an attempt to develop environmentally friendly polymer hybrids, biodegradable thermoplastic starch (TPS)/clay nanocomposites were prepared through melt intercalation method. Natural montrorillonite (Na⁺ MMT; Cloisite Na⁺) and one organically modified MMT with methyl tallow bis-2-hydroxyethyl ammonium cations located in the silicate gallery (Cloisite 30B) were chosen in the nanocomposite preparation. TPS was prepared from natural potato starch by gelatinizing and plasticizing it with water and glycerol. The dispersion of the silicate layers in the TPS hybrids was characterized by using wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). It was observed that the TPS/Cloisite Na⁺ nanocomposites showed higher tensile strength and thermal stability, better barrier properties to water vapor than the TPS/Cloisite 30B nanocomposites as well as the pristine TPS, due to the formation of the intercalated nanostructure. The effect of clay contents on the tensile, dynamic mechanical, and thermal properties as well as the barrier properties of the nanocomposites were investigated.     

Preparation and characterization of poly(methyl methacrylate)-clay nanocomposites via melt intercalation: Effect of organoclay on thermal, mechanical and flammability properties

The PMMA nanocomposites were prepared by melt processing method. The influence of organoclay loading on extent of intercalation, thermal, mechanical and flammability properties of poly(methyl methacrylate) (PMMA)-clay nanocomposites were studied. Three different organoclay modifiers with varying hydrophobicity (single tallow vs. ditallow) were investigated. The nanocomposites were characterized by using wide angle X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, differential scanning calorimetry (DSC), and tensile tests. The intercalation of polymer chain within the silicate galleries was confirmed by WAXD and TEM. Mechanical properties such as tensile modulus (E), tensile strength, percentage elongation at break and impact strength were determined for nanocomposites at various clay loadings. Overall thermal stability of nanocomposites increased by 16-17 °C. The enhancement in T_g of nanocomposite is merely by 2-4 °C. The incorporation of maleic anhydride as compatibilizer further enhanced all the properties indicating improved interface between PMMA and clay. The flammability characteristics were studied by determining the rate of burning and LOI.     

Polypropylene-blended organoclay nanocomposites – preparation,characterisation and properties

Intercalated/exfoliated nanocomposites of thermoplastic polyolefin (TPO) blended nanoclay (Cloisite 20?A and Cloisite 30B) were fabricated using melt extrusion process. Polypropylene grafted maleic anhydride (PP-g-MA) was used as a compatibiliser to improve the dispersibility of clay. TPO/nanoclay composites were prepared with different percentages of clay loading (3, 5 and 7?wt%) by adding PP-g-MA as a compatibiliser. The nanocomposites having 5?wt%C20A/5?wt% compatibiliser exhibited a remarkable improvement in mechanical (tensile modulus, flexural modulus and impact strength) and thermal (heat distortion temperature, HDT) properties. The thermal measurements have been carried out by differential scanning calorimetry, thermogravimetric analysis and HDT methods. Dynamic mechanical analysis studies indicated that PP macromolecules were intercalated or exfoliated between the interlayer of silicates. The morphology of nanocomposites was characterised by scanning electron microscopy (SEM) and X-ray diffraction (XRD) was used to find out the arrangement of crystals in the nanocomposites. The SEM and XRD clearly demonstrated the progressive break up of particles and results in decreased particle size with the optimised combination.     

Effect of temperature,duration and speed of pre-mixing on the dispersion of clay/epoxy nanocomposites

The effect of temperature, duration and speed of pre-mixing on the dispersion of organoclay in epoxy was studied. The technique of high-speed mixing process was used. Epoxy and Cloisite 30B were pre-mixed at different temperatures, different speeds and for different durations of time. The quality of dispersion and intercalation/exfoliation of organoclay in epoxy after pre-mixing (before adding hardener) was analyzed by means of X-ray diffraction (XRD) and viscosity measurement. The dispersion and intercalation/exfoliation of organoclay in the epoxy nanocomposites (ENCs) after curing were characterized by XRD, field emission gun scanning electron microscopy (FEGSEM) and TEM. The results illustrate that the clay particles were broken down to smaller and smaller sizes with increase of pre-mixing temperature and especially with increase in pre-mixing speed. These parameters do not significantly affect the intercalation/exfoliation of organoclay in epoxy at the pre-mixing step, but they have indirect effect on intercalation/exfoliation at the curing step.     

Structure and properties of nylon 6–clay nanocomposites: effect of temperature and reprocessing

Melt-compounding is a technique which has been commonly used for producing polymer–clay nanocomposites with enhanced mechanical, thermal, and physical properties. Twin-screw extruders have been found to effectively exfoliate the clay platelets due to their high shear intensity. However, concerns about polymer and organoclay degradation have been raised in some studies. In this investigation, a composite of nylon 6–Cloisite 30B with fully exfoliated and well-dispersed clay particles was produced using a single-screw extruder and hence with limited polymer degradation. We show that processing temperature plays an important role in enhancing dispersion and that reprocessing at a higher temperature can enhance both dispersion and exfoliation and thus can result in composites with superior properties. We attempt to elucidate how the change in melt viscosity—coupled with the change in processing temperature—affects clay exfoliation and dispersion.     

Morphology development and stability of polypropylene/organoclay nanocomposites

A series of polypropylene (PP)/organoclay nanocomposites with varied concentrations of clay, from 1 to 7 wt%, was successfully prepared via melt intercalation using a PP functionalized with maleic anhydride as compatibilizer. The morphology/property relationships of the nanocomposites were investigated by XRD, TGA and DSC analyses. Two distinct groups of composites, from a quasi-exfoliated to an intercalated/flocculated morphology, were identified. In particular, intercalated/flocculated morphologies were obtained for those composites with an organoclay concentration beyond the threshold (3 wt%), as evidenced by XRD analysis and confirmed by the increase of the glass transition temperature. This last effect was related to the confinement of polymer chains between the silicate layers, generating a reduction of the chain mobility. The variable increase of the thermal stability of the nanocomposites was also likely related to the different degree of exfoliation/intercalation of the samples. The toluene extraction of composites was used as a powerful methodology to distinguish between polymer phases differently interacting with the inorganic surface: composites having a semi-exfoliated structure were split into two fractions having a similar morphology. For those samples having the higher organoclay concentration and intercalated morphology, a toluene-residue fraction was obtained containing almost all the clay present in the pristine composite. Furthermore, in this case the morphological analysis of the residue fraction evidenced a collapse of the inorganic structure compared to that of the unextracted composite. A careful characterization of both soluble and residue fractions is reported and the results are discussed considering the interactions at the interface between the functionalized PP chains and silicate layers and their effects on the organoclay dispersion degree and stability.     

Influence of morphology on the dynamic mechanical characteristics of PP-EP/EVA/organoclay nanocomposites

A study on the dynamic mechanical properties of polypropylene copolymer/ethylene–vinyl acetate/organoclay (PP-EP/EVA/C20A) nanocomposites is presented. Nanocomposites were obtained by melt blending. Morphology consisting of intercalated–exfoliated clay nanolayers preferentially located within the EVA phase was observed by transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD). Polar groups of vinyl acetate in the EVA facilitated the polymer–clay interactions. Changes in the glass transition temperature (T_g) were correlated with changes in the clay intercalation–exfoliation levels. The highly reinforced with intercalated–exfoliated clay layers EVA phase was considered as the origin of the improvement on mechanical properties of the ternary nanocomposites and is associated with the increase on viscosity, heat deflection temperature (HDT), and storage modulus.     

Biodegradable aliphatic polyester-poly (epichlorohydrin) blend/organoclay nanocomposites; synthesis and rheological characterization

Polymer/organoclay nanocomposite systems were prepared from biodegradable aliphatic polyester (BAP)-poly(epichlorohydrin) (PECH) blends via the solvent casting method. From X-ray diffraction analysis, it was confirmed that the increased interlayer distance of the clay was solely affected by the BAP, implying that the BAP has better affinity to clay than PECH in a competitive intercalation mechanism. To clarify the sole effect of clay on polymer blend nanocomposite systems, we fixed the clay content at 3 wt%. The mechanical properties and rheological characteristics in steady and oscillatory shear modes of BAP-PECH/clay nanocomposites were investigated and compared with those of BAP-PECH blends without clay.     

Study of rheological properties of polypropylene/organoclay hybrid materials

Polypropylene nanocomposites reinforced with organic modified montmorillonite clay have been fabricated by melt compounding using extrusion. The morphology of the composites is studied with transmission electron microscopy and X-ray diffraction. The melt-state rheological properties of the nanocomposites have been investigated as a function of temperature and organoclay loading. It is found that the organoclays are intercalated and dispersed evenly in the matrix. The storage and loss moduli of the hybrid composites decrease with temperature and increase with organoclay concentration. Both polypropylene and its composites demonstrate a melt-like rheological behavior, indicating the low degree of exfoliation of the organoclay. A shear thinning behavior is found for both polypropylene and its composites, but the onset of shear thinning for organoclay composites occurs at lower shear rates.     

Melt processing of polypropylene/clay nanocomposites modified with maleated polypropylene compatibilizers

Maleic anhydride-grafted polypropylene (PPgMA) and organically modified clay composites were prepared in a plasticorder. PPgMAs, including PB3150, PB3200, PB3000, and E43, with a wide range of MA content and molecular weight were used. The structure was investigated with X-ray diffraction (XRD) and transmission electron microscopy (TEM). PPgMA compatibilizers gave rise to similar degree of dispersion beyond the weight ratio of 3 to 1 with the exception of E43, which had the highest MA content and the lowest molecular weight. It was found that thermal instability and high melt index were responsible for ineffective modification by E43. Furthermore, PPgMA with low melting point and high melt index was compounded at low equilibrium temperature in order to maintain a certain level of torque. We then modified polypropylene/organoclay nanocomposites with different levels of PPgMA compatibilizers on a twin-screw extruder. The PP/E43/clay system, as shown through XRD patterns and TEM observation, yielded the poorest clay dispersion among the compatibilizers under investigation. The relative complex viscosity curves also revealed a systematic trend with the extent of exfoliation and showed promise for quantifying the hybrid structure of the nanocomposites. Mechanical properties and thermal stability were determined by dynamical mechanical analysis and thermogravimetric analysis, respectively. Though PPgMA with lower molecular weight and higher MA content could lead to good clay dispersion in PP/clay composites, it caused the deterioration in both mechanical and thermal properties of PP/PPgMA/clay composites.     

Synthesis and properties of new polyimide/clay nanocomposite films

A series of polymer–clay nanocomposite (PCN) materials consisting of polyimide and typical clay were prepared by solution dispersion. Quaternary alkylammonium modified montmorillonite, Cloisite 20A, was used as organoclay. Poly(amic acid) solution was prepared from the reaction of benzophenone-4,4′,3,3′-tetracarboxylic dianhydride and 2-(5-(3,5-diaminophenyl)-1,3,4-oxadiazole-2-yl) pyridine in dimethylacetamide. Thermal imidization was performed on poly(amic acid)/organoclay dispersion in a regular temperature-programmed circulation oven. The study of interlayer d-spacing with X-ray diffraction pattern indicates that an exfoliated structure may be present in the nanocomposite 1%. Intercalated structures were obtained at higher organoclay loadings. Nanocomposites were studied using thermogravimertic analysis and differential scanning calorimetry. Nanocomposites exhibit higher glass transition temperature and improved thermal properties compared to neat polyimide due to the interaction between polymer matrix and organoclay particles. The results are also compared with data of a similar work. Morphology study with scanning electron microscopy showed that the surface roughness in nanocomposite 1% increased with respect to pristine polyimide. Solvent uptake measurements were also carried out for the prepared materials. Maximum solvent adsorption was observed for dimethyl sulfoxide (DMSO). It was found that the solvent uptake capacity decreased with increasing clay content.     

Blends and clay nanocomposites of cellulose acetate and poly(epichlorohydrin)

The aim of this work was to investigate cellulose acetate/poly(epichlorohydrin) (CA/PEPi) blends and cellulose acetate/poly(epichlorohydrin)/organically modified montmorillonite clay nanocomposites (CA/PEPi/MMTO) prepared by melt processing in a twin-screw extruder. The combination of an elastomer and clay in the cellulose acetate matrix was an attempt made to reach a balance between toughness and strength properties. The blend and nanocomposite structure, morphology and thermal properties were investigated by small angle X-ray scattering, transmission electron microscopy and dynamical mechanical analysis. The results showed immiscibility of the polymer components for all the CA/PEPi blend composition range investigated. In the case of the nanocomposites, the results indicated a significant polymer intercalation in the clay gallery as well as the exfoliation of the silicate layers. Moreover, the organoclay was present in the CA phase, but some of the organoclay migrated to the CA/PEPi interface and tended to surround the PEPi phase. The addition of PEPi elastomer to cellulose acetate showed a significant increase in the blend impact resistance. However the combination of PEPi and MMTO did not in fact produce a good stiffness versus toughness balance.     

聚氯乙烯/粘土纳米复合材料的制备及性能

通过原位插层法制备了聚氯乙烯／粘土纳米复合材料，分别采用X射线衍射，透射电子显微镜对其结构与形态进行了表征。结果表明，粘土片层已基本被刺离，均匀分散于聚氯乙烯树脂基体中。复合材料的力学性能和耐热性能测试结果表明，适量有机粘土的加入能使其拉伸强度和维卡软化点均较纯聚氯乙烯有较大提高。     

Preparation and characterization of poly(vinyl chloride) calcium carbonate nanocomposites via melt intercalation

Calcium carbonate was synthesized by in situ deposition technique and its nano size (35–60 nm) was confirmed by transmission electron microscopy (TEM). Composites of the filler CaCO₃ (micro and nano) and the matrix poly(vinyl chloride) (PVC) were prepared with different filler loadings (0–5 wt%) by melt intercalation. Brabender torque rheometer equipped with an internal mixer has been used for preparation of formulations for composites. The effect of filler content both nano- and micro level on the nanostructure and properties is reported here. The nanostructures were studied by wide angle X-ray diffraction and scanning electron microscopy. The mechanical, thermal, and dynamic mechanical properties of PVC/micro- and nano-CaCO₃ composites were characterized using universal testing machine, thermogravimetric analyzer, and dynamic mechanical analyzer. The results of thermal analysis indicated that the thermal stability of PVC/nano-CaCO₃ composites was improved as compared with corresponding microcomposites, and that of pristine PVC and maximum improvement was obtained at 1 and 3 phr loadings. However, the tensile strength decreased significantly with increase loading of both nano- and micro-CaCO₃, whereas storage modulus and glass transition temperature increased significantly.     

Intercalation behavior of polyimide/organoclay nanocomposites during thermal imidization

To understand the intercalation behavior of polyimide (PI)/clay nanocomposites during thermal imidization, two different types of poly(amic acid) (PAA) were synthesized, and the corresponding hybrids with organically treated clays (O-MMT) were also prepared. The changes in molecular structure of the polymer matrix, interlayer spacing, and fracture morphology with a series of thermal imidization steps were investigated. The PAA/clay nanocomposites initially showed two X-ray diffraction peaks, indicating two levels of intercalation. As the temperature at which the thermal imidization step was performed increased, the peak intensity of the higher angle peak increased, and it remained as a unique peak at 2θ=6.70 (d-spacing of 13.2 Å) for both PI(1), based on pyromellitic dianhydride (PMDA)+4,4′-oxydianiline (ODA), and PI(2), based on PMDA+4,4′-(9-fluorenylidene)-dianiline (9FDA). However, the lower angle peak became smaller and broader, and the angle became higher. This peak finally disappeared after thermal treatment at 300 °C for PI(1), but did not disappear completely for PI(2), although the peak showed a marked decrease in intensity and became broader.     

Preparing PP/clay nanocomposites using a swelling agent

Polypropylene (PP)/clay nanocomposites (PPCN) were prepared using a swollen organoclay, which had a larger interlayer spacing than pristine organoclay. The organoclay was first treated with a swelling agent (maleic anhydride, MA) and a co-swelling agent in solution. Then, it was melt blended with PP-g-MA to generate a pre-intercalated composite (PIC). Finally, the PIC was blended with PP to obtain a PPCN, which contained small amounts of PP-g-MA. The materials were characterized using X-ray diffraction (XRD), Scanning electron microscopy, Transmission electron microscopy (TEM), and TGA. The XRD graphs showed that the basal spacing of the pristine clay treated with MA was 1.6 nm, which was larger than that of the original clay, but smaller than that of the organoclay. The XRD graphs of the organoclay treated with MA showed double peaks at 3 and 5.5°. As the ratio of MA to the organoclay increased, the peak at 5.5° decreased gradually. TEM micrographs indicated that the clay layers in the pre-intercalated blends were still stacked in an orderly manner. However, partial exfoliation of the clay layers was observed in the PPCN. The nanocomposites prepared with the aid of swelling agents contained some PP-g-MA. Good dispersion of the clay layers gave the PPCN greater thermal stability and an enhanced storage modulus, which indicated a reinforcing effect of the clay in the PP matrix. The increased T_g (derived from Dynamic mechanical analysis) of PPCN implied that the PP macromolecules were intercalated between interlayers of the silicate.     

熔体插层制备EVA/粘土纳米复合材料

通过熔体插层制备了乙烯-乙酸乙烯酯共聚物(EVA)／粘土纳米复合材料。采用FT-IR、XRD、TG分析和力学性能测试研究了有机改性粘土和EVA/粘土复合材料的结构与性能。实验结果表明，通过离子交换反应，可使长链十八胺阳离子嵌入粘土片层间，增大了粘土的片层间距；对于EVA／有机化粘土体系，通过熔体插层可使EVA分子链插层于粘土片层中，使粘土片层被进一步撑开；EVA／粘土纳米复合材料具有较好的力学性能。     

Chlorinated polyethylene nanocomposites: thermal and mechanical behavior

Chlorinated polyethylene (CPE) nanocomposites prepared with natural and organically treated montmorillonite (MMT) clays by solution intercalation method were investigated. X-ray diffraction and transmission electron microscopy techniques showed separation of organically modified clay MMT layers and indicated formation of exfoliated nanocomposites. Fourier transform infrared spectroscopy results showed interaction between the CPE matrix and the clay intercalants of Cloisite^® 30B and Cloisite^® 15A (natural MMT modified with quaternary ammonium salts). Organically treated MMT clays were found to be better dispersed in CPE in comparison to natural MMT clay. Mechanical testing showed enhanced tensile strength, Young’s modulus, and storage modulus of chlorinated-polymers/organically treated MMT clay nanocomposites. Significant improvements in the above properties were obtained with Cloisite^® 15A nanoclay. The temperature, at which maximum degradation occurred, was higher for the nanocomposite having 5 wt% Cloisite 15A than that of neat CPE. Differential scanning calorimetric results revealed that the same composition also absorbed more heat during the heating, indicating better thermal stability. CPE rubber nanocomposite could be a promising heat resistant polymeric material.     

The effect of process parameters on physical and mechanical properties of commercial low density polyethylene/ORG-MMT nanocomposites

Polyethylene/organo-montmorillonite clay (org-MMT) nanocomposites were prepared utilizing PP-g-MA as a compatibilizer by melt intercalation method. In order to increase the miscibility of polyethylene (PE) with nanoparticle surface at firs, a primary masterbatch consist of compatibilizer and org-MMT was prepared then, this compound was melt intercalated with PE to synthesis the PE/org-MMT nanocomposites. In this study, the presence of commercial low density polyethylene in Nanocomposites structure and also the effect of process parameters such as: amount of nanoparticles, mixing rate and mixing time on nanocomposite structure and properties have been investigated. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that the interlayer distance of nanoparticle layers increased and a partially intercalated structure was prepared by melt intercalation method. Interaction between polyethylene chains and nanoparticle layers could be improved if the control of above parameters causes to penetrate the chains into nanoclay layers; by an optimization, this effect could improve the physical and mechanical properties. The DSC data revealed that melting temperature has slowly increased and crystalinity has lightly decreased. Consequently we can claim the thermal properties of LDPE/clay nanocomposite did not considerably change with clay content. A rise in the mechanical properties such as yield stress and modulus was observed by tension test; by addition of 5% clay content the tensile strength increased about 7%, the tensile modulus enhanced about 60% and the yield stress increased about 16% in comparison with the pure LDPE.     

Itaconic acid and amino alcohol functionalized polyethylene as compatibilizers for polyethylene nanocomposites

The compatibilization provided by itaconic acid (IA) and 2-[2-(dimethylamino)-ethoxy] ethanol (DMAE) functionalized polyethylene for forming polyethylene-based nanocomposites was studied and compared. IA was grafted into PE by melt mixing to obtain PEgIA (compatibilizer 1), thereafter, PEgIA was reacted with DMAE also by melt mixing to obtain PAgDMAE (compatibilizer 2). PE-clay nanocomposites were prepared by melt mixing polyethylene with each of the two quaternary ammonium modified montmorillonite clays (Cloisite 30B and Nanomer I28E) plus each of the two previously prepared compatibilizers (PEgIA and PEgDMAE). FTIR characterization confirmed the formation of these two compatibilizers. All the compatibilized nanocomposites had better clay exfoliation–intercalated compared to the uncompatibilized PE nanocomposites. X-ray diffraction and transmission electron microscopy results, as well as the mechanical properties attained showed that the PEgDMAE with the I28E clay produced the better exfoliated–intercalated nanocomposites. Samples with C30B clay did not show any intercalation improvement, as compared to the uncompatibilized samples, which was attributed mainly to the smaller initial intergallery spacing of this clay. Finally, it is concluded that the PEgDMAE offers an outstanding capability for preparing highly exfoliated PE clay nanocomposites.