Electron beam crosslinking of non-lead PVC formulations

PVC samples with lead-free and lead-base stabilizer, containing TMPTMA (trimethylolpropane trimethacrylate) as a crosslinker and DOP (2-ethylhexyl phthalate) as a plasticizer, were electron beam treated at different doses (2–200 kGy) and characterized to evaluate crosslinking and other several properties, as a continuation of our previously reported paper, where these PVC formulations, typical for wire and cable applications, underwent gamma irradiation. The PVC was formulated with two different stabilizing systems: Ca/Zn and dibasic lead phthalate for comparison, to use them as jackets for a 22 wire gage (AWG). Small samples of the jacketed wires were irradiated in an industrial Dynamitron electron accelerator for the corresponding doses, along with two dosimetric systems: radiochromic thin film and alanine pellets dosimeters. The maximum dose applied was decided as the crosslinking increased, until the gel content was stable. The dose of 200 kGy was the condition for the highest crosslinking, so most of the wire was irradiated at such dose. Chemical and mechanical evaluations were carried out to the irradiated wire. The results show that 200 kGy was too high dose for the materials, since an important degradation is observed for the Ca/Zn systems. Unfortunately, such dose affects basically to CaZn formulations, which showed much poorer performance than classical lead-containing compositions. The results also indicate that gel content is not the best way of deciding the optimum condition for irradiation.     

Electrospinning of poly(ethylene-co-vinyl acetate)/clay nanocomposite fibers

Poly(ethylene-co-vinyl acetate)/clay nanocomposite fibers were fabricated using electrospinning. The fiber diameters were controlled by varying the polymer/chloroform concentration, which resulted in fibers with diameters ranging from 1 to 15 μm. The clay concentration was varied from 0.35 to 6.6 wt %. Scanning electron microscopy revealed that the fiber diameter increased with increasing clay concentration, whereas beading decreased. Transmission electron microscopy revealed a disruption of the spherulite structures by clay, which is consistent with heterogeneous nucleation. Shear modulus force microscopy indicated a reduction in melting point (T_m) with decreasing diameter for fibers thinner than 15 μm, which was confirmed by temperature dependent X-ray diffraction data. For fibers thinner than 8 μm, the presence of clay further enhanced the reduction of T_m. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2501–2508, 2009     

Effect of the urethane group on treated clay surfaces for high-performance poly(butylene succinate)/montmorillonite nanocomposites

We successfully modified organic clays containing the urethane group by introducing a covalent bond between the silanol group on the clay side and the hydroxyl group of organic modifier in the silicate layer using 1,6-diisocyanatohexane (HDI), namely surface-treated montmorillonite (30BM), to increase both basal spacing and the favorable interaction between clay and polymer. The effect of the surface urethane modification of clay on poly (butylene succinate) (PBS)/30BM nanocomposites was studied. The results of transmission electron microscopy micrographs at a 10-nm resolution and X-ray diffraction measurements allowed us to examine the degree of the high exfoliation and the effect of surface urethane modification on clay dispersibility. As results of high exfoliation, PBS/30BM nanocomposites not only exhibited the high thermal properties, but also showed a remarkable increase in physical properties (e.g., tensile strength, Young's modulus, elongation at break) due to enhanced affinity between the clay and PBS matrix. Over all, the results suggest that wide gallery spacing and the predominant affinity between PBS and clay must be considered simultaneously to increase the degree of exfoliation and physical properties as key factors.     

Degradation of poly(ethylene terephthalate)/clay nanocomposites during melt extrusion: Effect of clay catalysis and chain extension

Organoclays with various contents of hydroxyl groups and absorbed ammonium were prepared and compounded with poly(ethylene terephthalate) (PET), forming PET/clay nanocomposites via melt extrusion. Dilute solution viscosity techniques were used to evaluate the level of molecular weight of PET/clay nanocomposites. Actually, a significant reduction in PET molecular weight was observed. The level of degradation depended on both the clay structure and surfactant chemistry in organoclays. The composites, based on clay with larger amount of hydroxyl groups on the edge of clay platelets, experienced much more degradation, because the hydroxyl groups acted as Brønsted acidic sites to accelerate polymer degradation. Furthermore, organoclays with different amounts of absorbed ammonium led to different extents of polymer degradation, depending upon the acidic sites produced by the Hofmann elimination reaction of ammonium. In addition, the composite with better clay dispersion state, which was considered as an increasing amount of clay surface and ammonium exposed to the PET matrix, experienced polymer degradation more seriously. To compensate for polymer degradation during melt extrusion, pyromellitic dianhydride (PMDA) was used as chain extender to increase the intrinsic viscosity of polymer matrix; more importantly, the addition of PMDA had little influence on the clay exfoliation state in PET/clay nanocomposites.     

Electron beam crosslinking of poly(vinylmethyl ether)

The electron beam induced branching of poly(vinylmethyl ether) (PVME) in bulk and in isopropanol solutions has been studied by gel permeation chromatography. The branching probability of bulk PVME induced by high-energy electrons can be characterized by gel permeation chromatography and a simple probability constant obtained. In isopropanol solutions this branching probability is not constant as a function of dose and is found to decrease with decreasing concentration. These results indicate the importance of solvent effects on the crosslinking of PVME in isopropanol solution by electron beam radiation. © 1994 John Wiley & Sons, Inc.     

Influence of clay surface modification with urethane groups on the crystallization behavior of in situ polymerized poly(butylene succinate) nanocomposites

The crystallization behavior and fine structure of poly(butylene succinate) (PBS) nanocomposites with intercalation (30B20) and exfoliation (30BM20) morphologies, respectively, were investigated via isothermal crystallization testing and synchrotron small-angle X-ray scattering (SAXS). The dynamic viscosity of 30BM20 was markedly increased due to favorable interactions between the PBS matrix and the urethane group on the clay surface. However, 30BM20 showed similar crystallization rates to that of homo PBS because the surface urethane modification for 30BM20 precluded PBS matrix from the metallic group into clay to difficult in contact with each other, resulting in a reduced nucleation activity for the metallic group. SAXS profiles revealed that the long period and amorphous region size for 30B20 drastically decreased during isothermal crystallization. Meanwhile, 30BM20 was similar to those of homo PBS. This result also supports the above explanation for isothermal crystallization behavior. Considering all results in total, the introduction of a urethane modification considerably enhanced the physical properties of PBS but caused delayed crystallization rates.     

Influence of gamma irradiation on the ageing characteristics of poly(ethylene-co-vinyl acetate) and poly(ethylene-co-vinyl acetate)/carbon black mixture

In this comparative study, the effect of gamma rays on the ageing characteristics of poly(ethylene-co-vinyl acetate) (EVA) and poly(ethylene-co-vinyl acetate)/carbon black mixture (EVA/CB) was investigated in terms of thermal stability. EVA, containing 13% vinyl acetate (VA), and EVA/CB, containing 13% VA and 1% carbon black (CB), were aged at 85°C in air up to 30 weeks for thermal ageing. Same substances were aged by means of UV light with a wavelength in the vicinity of 259 nm, in air, up to 400 h for UV ageing. Same substances were also irradiated with gamma rays at ambient conditions up to 400 kGy. Following these experiments, samples which had been irradiated with gamma rays, were subjected to thermal and UV ageing under the same conditions as for unirradiated samples. Dynamic thermogravimetry studies were performed for determination of the thermal stabilities of the samples. 10 and 50% mass losses were calculated for the samples from their respective curves. As a result of thermal analysis experiments, it was found that CB dramatically loses its protective property against thermal ageing of EVA after gamma irradiation. On the other hand, gamma irradiation does not have any significant effect on the UV ageing characteristics of EVA and EVA/CB in terms of thermal stability.     

Crystallization, morphology, and dynamic mechanical properties of poly(trimethylene terephthalate)/clay nanocomposites

The poly(trimethylene terephthalate) (PTT)/clay nanocomposite has been successfully prepared via melt intercalation using a co-rotating twin screw extruder. The nanocomposite was characterized by wide angle X-ray diffraction (WAXD), transmission electron microscope (TEM), differential scanning calorimetry (DSC), polarized light microscope (PLM) and dynamic mechanical analysis (DMA). The nanocomposite forms an exfoliated structure, which can be observed by WAXD and TEM. The effect of clay layers on the crystallization behaviors of PTT was studied through isothermal and non-isothermal crystallization methods. The results suggest that the introduction of nanosize clay layers accelerates the crystallization rate of PTT and the clay layers act as nucleation agents. The morphology of spherulites was investigated with PLM and the result is well in agreement with crystallization kinetics. DMA shows that glass transition temperature (T_g) and storage modulus (E^′) of the PTT matrix of the nanocomposite are higher than those of pure PTT.     

Polypropylene-clay nanocomposites: effect of compatibilizing agents on clay dispersion

In this work, polypropylene-clay nanocomposites are obtained and studied by using two different coupling agents, diethyl maleate and maleic anhydride. Two different clays, a commercial montmorillonite (Nanomer I30.TC) and a sodium bentonite purified and modified with octadecylammonium ions have also been used. The relative influence of each factor, matrix and clay modification, can be observed from structural analysis (SAXS, TEM) and mechanical properties. An explanation of the results is proposed according to the microstructure and chemical nature of the systems and the thermodynamic interactions operating during nanocomposite preparation.     

Preparation and thermal stability of boron-containing phenolic resin/clay nanocomposites

In order to further improve thermal stability of the phenolic resins, we combined boron and clay with phenolic resins to prepare nanocomposites (BH-B, BP-B, and BE-B series). Boron-containing phenolic resin/clay (montmorillonite) nanocomposites were prepared using in situ polymerization of resol-type phenolic resins. Montmorillonite (MMT) was modified by benzyldimethylhexadecylammonium chloride (BH), benzyldimethyphenylammonium chloride (BP), and benzyltriethylammonium chloride (BE). X-ray diffraction measurements and transmission electron microscope (TEM) observations showed that clay platelets were partially exfoliated after complete curing of the phenolic resins. Thermogravimetric analysis showed that thermal decomposition temperatures (T_d) and residual weight at 790 °C of cured boron-containing nanocomposites were much higher than the corresponding nanocomposites without boron. For example, the rise in decomposition temperature of BE-B10% is about 42 °C (from 520 to 566 °C), whereas the increase in char yields is 6.4% (from 66.2% to 72.6%). However, the boron-containing composites were more prone to absorb moisture (ca. 9-14%) than boron-free ones (ca. 3-4%), which was attributed to unreacted or partially reacted boric acid during preparation process.     

Electron beam irradiation effects on poly(ethylene terephthalate)

Changes in poly(ethylene terephthalate) subjected to electron beam irradiation at doses up to 15 MGy and dose rate of 1.65 MGy/h, were investigated by differential scanning calorimetry, molecular weight measurement, X-ray photoelectron spectroscopy, and scanning electron microscopy. Irradiated samples showed a decrease of molecular weight with a minimum at 5 MGy, which is attributed to chain scission of the macromolecules and then an increase at further doses due to branching and some degradation effect. Irradiation in air is not an important factor because the high dose rate of irradiation inhibits oxygen diffusion in the samples.     

Rheology and thermal stability of polylactide/clay nanocomposites

Polylactide/clay nanocomposites (PLACNs) were prepared by melt intercalation. The intercalated structure of PLACNs was investigated using XRD and TEM. Both the linear and nonlinear rheological properties of PLACNs were measured by parallel plate rheometer. The results reveal that percolation threshold of the PLACNs is about 4 wt%, and the network structure is very sensitive to both the quiescent and the large amplitude oscillatory shear (LAOS) deformation. The stress overshoots in the reverse flow experiments were strongly dependent on the rest time and shear rate but shows a strain-scaling response to the startup of steady shear flow, indicating that the formation of the long-range structure in PLACNs may be the major driving force for the reorganization of the clay network. The thermal behavior of PLACNs was also characterized. However, the results show that with the addition of clay, the thermal stability of PLACNs decreases in contrast to that of pure PLA.     

Toughening of ethylene-propylene random copolymer/clay nanocomposites: Comparison of different compatibilizers

Ethylene/propylene-random-copolymer(PPR)/clay nanocomposites were prepared by two-stage melt blending. Four types of compatibilizers,including an ethylene-octene copolymer grafted maleic anhydride(POE-g-MA) and three maleic-anhydride-grafted polypropylenes(PP-g-MA) with different melt flow indexes(MFI),were used to improve the dispersion of organic clay in matrix.On the other hand,the effects of organic montmorillonite(OMMT) content on the nanocomposite structure in terms of clay dispersion in PPR matrix,thermal behavior and tensile properties were also studied. The X-ray diffraction(XRD) and transmission electron microscopy(TEM) results show that the organic clay layers are mainly intercalated and partially exfoliated in the nanocomposites.Moreover,a PP-g-MA compatibilizer(compatibilizer B) having high MFI can greatly increase the interlayer spacing of the clay as compared with other compatibilizers.With the introduction of compatibilizer D(POE-g-MA),most of the clays are dispersed into the POE phase,and the shape of the dispersed OMMT appears elliptic,which differs from the strip of PP-g-MA.Compared with virgin PPR,the Young’s modulus of the nanocomposite evidently increases when a compatibilizer C(PP-g-MA) with medium MFI is used.For the nanocomposites with compatibilizer B and C,their crystallinities(X_c) increase as compared with that of the virgin PPR. Furthermore,the increase of OMMT loadings presents little effect on the melt temperature(T_m) of the PPR/OMMT nanocomposites,and slight effect on their crystallization temperature(T_c).Only compatibilizer B can lead to a marked increases in crystallinity and T_c of the nanocomposite when the OMMT content is 2 wt%.     

Influence of four different types of organophilic clay on the morphology and thermal properties of polystyrene/clay nanocomposites prepared by using the γ-ray irradiation technique

Polystyrene (PS)/clay nanocomposites were successfully prepared by the γ-ray irradiation technique. Four different types of organophilic clays were used: three of the four contained a reactive group, while the other did not. Exfoliated PS/clay nanocomposites can be obtained by using reactive organophilic clay and intercalated PS/nanocomposites can be formed by using non-reactive ones, which was confirmed by X-ray diffraction (XRD) and by transmission electron microscopy (TEM). In the formation of exfoliated PS/nanocomposites, the effect of the double bond of the clay-intercalated agents is much more important than the alkyl chain length. The enhanced thermal properties of PS/nanocomposites were characterized by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). In particular, the enhancement of the thermal properties of PS/nanocomposites made using the reactive organophilic clay was much higher than that of the thermal properties of PS/nanocomposites incorporating non-reactive clay.     

Effect of epoxy resin on rheology of polycarbonate/clay nanocomposites

Polycarbonate/clay nanocomposites (PCNs) were prepared by melt intercalation using epoxy resin as a compatibilizer. The intercalated structure of PCNs was investigated using XRD and TEM. The linear and nonlinear dynamic rheological properties of PCNs were measured by the use of a parallel plate rheometer. The results reveal that the presence of epoxy influences rheological behavior of PCNs significantly. Addition of epoxy can improve dispersion of clay, enhancing the low-frequency viscoelastic responses; while high loadings of epoxy lead to a severe degradation of PC matrix, decreasing the high-frequency responses together with the plasticizing effect of excessive epoxy. Both of these two effects result in invalidity of time-temperature superposition. Moreover, all samples show high sensitivity to both the quiescent and large amplitude oscillatory shear (LAOS) deformation, despite enhanced percolation of tactoids due to the compatibilization of epoxy.     

Structure and properties of poly(vinyl chloride)/graphene nanocomposites

The goal of the paper was to investigate the influence of graphene (GN) on properties and structure of suspensive poly(vinyl chloride) (PVC). PVC/GN nanocomposites were obtained by the solvent evaporation method, and their structures were evaluated using optical microscopy, SEM, FT-IR, XRD and Raman spectroscopy methods. Thermal properties of the obtained materials were studied by TGA. Electrical properties and swelling behaviour were also determined.The microscopic observations confirm a uniform distribution of graphene in the PVC matrix. The investigations carried out indicated an effect of graphene on a decrease in resistivity to a value which enabled to include the PVC/GN nanocomposites into anti-static materials group. On the basis of swelling studies, it has been found that the PVC/GN nanocomposites have a higher chemical resistance against acetone while compared to pure poly(vinyl chloride). The properties of the obtained materials depend significantly on content and dispersion level of graphene in the PVC matrix. An impact of GN on the acceleration of the PVC degradation process was found.     

Prevulcanized natural rubber latex/clay aerogel nanocomposites

Natural rubber latex (NR)/clay aerogel nanocomposites were produced via freeze-drying technique. The pristine clay (sodium montmorillonite) was introduced in 1-3 parts per hundred rubber (phr) in order to study the effect of clay in the NR matrix. The dispersion of the layered clay and the morphology of the nanocomposites were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Cure characteristics, thermal stability, and the crosslink density of thermal and microwave-cured NR and its composites were investigated. XRD patterns indicated that both intercalated and exfoliated structures were observed at loadings of 1-3 phr clay. SEM studies revealed that the clay aerogel structure was formed at 3 phr clay loading. The increment in Shore A hardness of nanocomposites compared with pure NR signified excellent polymer/filler interaction and the reinforcing effect of the clay to rubber matrix. This was supported by an increase in maximum rheometric torque and crosslink density. The crosslink density of clay-filled NR vulcanizate was found to increase with the pristine clay content in both thermal and microwave curing methods. However, microwave-cured 2 and 3 phr-filled NR vulcanizates exhibited higher crosslink density than those which were thermal-cured under the same curing temperature. In addition, thermal stability studies showed that pristine clay accelerated the decomposition of NR by showing a slight decrease in onset and peak decomposition temperatures along with clay content.     

Poly(vinyl alcohol)/GO-MMT nanocomposites: Preparation,structure and properties

A facile, efficient and environment friendly method is established to prepare poly(vinyl alcohol)(PVA) based graphene oxide-montmorillonite(GO-MMT) nanocomposites in aqueous media. GO-MMT nanohybrid is obtained by the combination of GO and MMT in water without any reducing or stabilizing agents. The formation of GO-MMT nanohybrid is due to the hydrogen bonding and crosslinking effects. The sodium ions within MMT sheets act as crosslinkers between GO sheets and MMT platelets. The resultant nanocomposites are characterized by means of X-ray diffraction(XRD), scanning electron microscopy(SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA) and mechanical testing. Compared to that of pure PVA, PVA nanocomposites show enhanced thermal stabilities and mechanical properties, which results from strong interfacial adhesion of the nanoadditives in PVA matrix. The further increase in the tensile strength and modulus results from strong interaction between PVA chains and layered GO-MMT as well as good mechanical properties of GO-MMT hybrid, compared to PVA/GO and PVA/MMT nanocompsoites.     

Polymorphism behavior of poly(ethylene naphthalate)/clay nanocomposites

Thermally stable organically modified clays based on 1,3‐didecyl‐2‐methylimidazolium (IM2C10) and 1‐hexadecyl‐2,3‐dimethyl‐imidazolium (IMC16) were used to prepare poly(ethylene naphthalate) (PEN)/clay nanocomposites via a melt intercalation process. The clay dispersion in the resulting hybrids was studied by a combination of X‐ray diffraction, polarizing optical microscopy, and transmission electron microscopy. It was found that IMC16 provided better compatibility between the PEN matrix and the clay than IM2C10, as evidenced by some intercalation of polymer achieved in the PEN/IMC16‐MMT hybrid. The effects of clay on the crystal structure of PEN were investigated. It was found that both pristine MMT and imidazolium‐treated MMT enhanced the formation of the β‐crystal phase under melt crystallization at 200 °C. At 180 °C, however, the imidazolium‐treated MMT was found to favor the α‐crystal form instead. The difference in clay‐induced polymorphism behavior was attributed to conformational changes experienced by the clay modifiers as the crystallization temperature changes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1040–1049, 2006     

Transesterification catalysts to improve clay exfoliation in synthetic biodegradable polyester nanocomposites

We report here on the melt intercalation preparation of polymer/clay nanocomposites based on three commercial synthetic biodegradable polyesters: EastarBio Ultra, Ecoflex, and Bionolle, respectively. The montmorillonite clay addition is performed either by direct dispersion of Cloisite 30B in the polyester matrix or by dispersing a “PCL-grafted Cloisite 30B” masterbatch in the biodegradable polyesters. All obtained nanocomposites display an intercalated morphology as attested by X-ray diffraction measurements. The various analyses clearly show that the Bionolle (BIO) matrix gives the best results. Morphological characterization and mechanical properties of these nanocomposites also show that the “masterbatch route” leads to poor results as a consequence of the very low compatibility between the poly(ε-caprolactone) (PCL) of the masterbatch and the three other polyester matrices. In a second part, nanocomposites based on the BIO matrix are prepared by direct dispersion of the organo-clay in the presence of three different metal-based catalysts with the aim to promote transesterification reactions between the nanocomposite constituents. The mechanical properties and morphological characterization of these nanocomposites show that the tin-based catalyst (Sn) is the more efficient. Indeed, the effectiveness of transesterification reactions taking place between the ester functions of the BIO matrix and the hydroxyl groups of the organo-clay and the resulting “grafting” of BIO chains on the organo-clay surface are confirmed by thermogravimetric analyses performed after the extraction procedure. TEM observations show that this catalyst enhances the clay platelets exfoliation within the BIO matrix as a consequence of the transesterification reactions. Nanocomposites prepared in presence of Sn show better clay dispersion and enhanced stiffness with a 60% increase in Young’s modulus.