Mechanical properties and morphology of polypropylene‐calcium carbonate nanocomposites prepared by dynamic packing injection molding

In this article, dynamic packing injection molding (DPIM) technology was used to prepare injection samples of Polypropylene‐Calcium Carbonate (PP/CaCO₃) nanocomposites. Through DPIM, the mechanical properties of PP/nano‐CaCO₃ samples were improved significantly. Compared with conventional injection molding (CIM), the enhancement of the tensile strength and impact strength of the samples molded by DPIM was 39 and 144%, respectively. In addition, the tensile strength and impact strength of the PP/nano‐CaCO₃ composites molded by DPIM increase by 21 and 514%, respectively compared with those of pure PP through CIM. According to the SEM, WAXD, DSC measurement, it could be found that a much better dispersion of nano‐CaCO₃ in samples was achieved by DPIM. Moreover, γcrystal is found in the shear layer of the DPIM samples. The crystallinity of PP matrix in DPIM sample increases by 22.76% compared with that of conventional sample. The improvement of mechanical properties of PP/nano‐CaCO₃ composites prepared by DPIM attributes to the even distribution of nano‐CaCO₃ particles and the morphology change of PP matrix under the influence of dynamic shear stress. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Study on the Improvement of Crystallization in HDPE Induced by High–Molecular-Weight Polyethylene Through Dynamic Packing Injection Molding

The effect of high–molecular-weight polyethylene (HMWPE) on crystal morphology was investigated for high-density polyethylene (HDPE) through dynamic packing injection molding (DPIM). With the aid of differential scanning calorimetry (DSC), wide-angle x-ray diffraction (WAXD), and scanning electron microscopy (SEM) measurements, a typical web-like shish kebab morphology, which markedly increases stiffness and toughness, was found in HMWPE-induced samples through DPIM. The SEM results show that the much better web-like shish kebab structure, in which most of the lamellae connect different columns, compared with conventional shish kebab, was formed in HDPE blends with 4% HMWPE content (B4) through DPIM. The WAXD studies indicate that orientation degrees of crystallographic planes (110) and (200) in the B4 samples were much higher than those of samples molded by static packing injection molding and B0 samples molded by DPIM. A combination of the higher degree of crystal orientation and the formation of web-like shish kebab led to simultaneous great increments of stiffness and toughness, which overcomes the traditional limitation that stiffness and toughness cannot be greatly enhanced simultaneously. All these results show that HWMPE favored for great improvement of crystal structures in HDPE when its content is appropriate through DPIM.     

Combined effect of shear and nucleating agent on the multilayered structure of injection‐molded bar of isotactic polypropylene

Molten polymers are usually exposed to varying levels of shear flow and temperature gradient in most processing operations. Many studies have revealed that the crystallization and morphology are significantly affected under shear. A so‐called “skin‐core” structure is usually formed in injection‐molded semicrystalline polymers such as isotactic polypropylene (iPP) or polyethylene (PE). In addition, the presence of nucleating agent has great effect on the multilayered structure formed during injection molding. To further understand the morphological development in injection‐molded products with nucleating agent, iPP with and without dibenzylidene sorbitol (DBS) were molded via both dynamic packing injection molding (DPIM) and conventional injection molding. The structure of these injection‐molded bars was investigated layer by layer via SEM, DSC, and 2 days‐WAXD. The results indicated that the addition of DBS had similar effect on the crystal size and its distribution as shear, although the later decreased the crystal size more obviously. The combination of shear and DBS lead to the formation of smaller spherulites with more uniform size distribution in the injection‐molded bars of iPP. A high value of c‐axis orientation degree in the whole range from the skin to the area near the core center was obtained in the samples molded via DPIM with or without DBS, while in samples obtained via conventional injection molding, the orientation degree decreased gradually from the skin to the core and the decreasing trend became more obvious as the concentration of DBS increased. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanical Properties and Crystal Structure of HDPE Induced by Small Amount of High-molecular-weight and Low-molecular-weight Polyethylene under Shear Stress Produced by Dynamic Packing Injection Molding

In order to better understand the effect of small amount of both high-molecular-weight polyethylene (HMWPE) and low-molecular-weight polyethylene (LMWPE) on the mechanical properties and crystal morphology under the shear stress field, the dynamic packing injection molding (DPIM) was used to prepare the oriented pure polyethylene samples and its blends ones with different contents of HMWPE and LMWPE. The experiment substantiated that the further improvement of tensile strength and impact stength along the flow direction (MD) of HDPE/HMWPE/LMWPE samples was achieved, while the tensile strength along the transverse direction (TD) still substantially exceeded that of conventional molding. When the contents of HMWPE and LMWPE were respectively 8% in blends, the tensile strength in both flow and transverse directions of the samples were highly enhanced, with improvements from 27.75 MPa to 115.43 MPa (about 316%), in MD and from 23MPa to 32.74 MPa (about 42.34%), in TD; besides the impact strength was improved from 21.55 KJ/m² to 72.6 KJ/m² (about 236.89%), in MD but decreased from 17 KJ/m² to 6.92 KJ/m² in TD. The obtained samples were characterized via DSC, WAXD and SEM. For HDPE/HMWPE/LMWPE, the shish-kebab structure which is composed of stretched chains (shish) and lamellae (kebab) was seen in the oriented region of DPIM samples and the spherulites existed in the oriented region of SPIM samples. Furthermore, the appropriate amount HMWPE and LMWPE (about 8%, respectively) blended into mixture can improve the thickness and the length of lamellae, and the degree of crystallinity in shear region by DPIM which were approved by DSC and SEM, at the same time, it can also enhance the intensity of orientation of lamellae in shear region confirmed by SEM and WAXD. The reason of improvement of mechanical properties is the existence of these thicker, longer and more orientated lamellae in shear region.     

Morphologies and mechanical properties of HDPE induced by small amount of high‐molecular‐weight polyolefin and shear stress produced by dynamic packing injection molding

To better understand the effect of a small amount of high‐molecular‐weight polyethylene (HMWPE) on the mechanical properties and crystal morphology under the shear stress field, the dynamic packing injection molding (DPIM) was used to prepare the oriented pure polyethylene and its blends with 4% HMWPE. The experiment substantiated that the further improvement of tensile strength along the flow direction (MD) of high‐density polyethylene (HDPE)/HMWPE samples was achieved, whereas the tensile strength along the transverse direction (TD) still substantially exceeded that of conventional molding. Tensile strength in both flow and TDs were highly enhanced, with improvements from 23 to 76 MPa in MD and from 23 to 31 MPa in TD, besides the toughness was highly improved. So, the samples of HDPE/HMWPE transformed from high strength and brittleness to high strength and toughness. The obtained samples were characterized via SEM and TEM. For HDPE/HMWPE, the lamellae of the one shish‐kebab in the oriented region may be stretched into other shish‐kebab structures, and one lamella enjoys two shish or even more. This unique crystal morphology could lead to no yielding and necking phenomena in the stress–strain curves of HDPE/HMWPE samples by DPIM. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of graphene nanoplatelets presence on the morphology,structure, and thermal properties of polypropylene in fiber melt‐spinning process

Melt spinning of graphene nanoplatelets (GnPs)‐polypropylene (PP) nanocomposite fibers are reported for the first time. PP/GnPs fibers were spun with a pilot‐plant spinning machine with varying concentration of GnPs by mixing PP/GnPs masterbatch with PP. The effect of inclusion of GnPs on the morphology and crystalline structure of PP fibers was investigated. The thermal stability of the fibers was also evaluated by thermogravimetric analysis. The light microscopy images showed that the GnPs are uniformly distributed over the PP matrix. The differential scanning calorimetry (DSC) results revealed that presence of GnPs affects both the melting and crystallization behaviors. The melting peaks of PP/GnPs nanocomposite fibers were broader than that of neat PP fibers, indicating a broader crystal size distribution in PP/GnPs nanocomposite fibers as compared to the neat PP fibers. Besides, an obvious increment in the crystallization peak temperature was observed in GnPs‐PP nanocomposite fibers. The wide‐angle X‐ray diffraction spectra (WAXD) results showed that the crystal type of nanocomposite fibers did not change and was still the α‐monoclinic crystal form. Moreover, the morphology of spherulites demonstrated that GnPs increased the nucleation sites in the nanocomposite fibers which in turn restricted the crystal growth of PP chains. This finding supported the DSC and WAXD results. Activation energies were calculated by Horowitz and Metzger's method as 77.87 and 105.41 kJ/mol for neat PP and PP/0.2 wt% GnPs fibers, respectively, suggesting an increase in the thermal stability of GnPs‐PP nanocomposite fibers. POLYM. COMPOS., 36:367–375, 2015. © 2014 Society of Plastics Engineers     

Effects of liquid crystal polymer and organoclay addition on the physical properties of high‐density polyethylene films

In this study, physical properties of high‐density polyethylene (HDPE) films, blended and reinforced with small amounts of liquid crystal polymer (LCP) and organoclay (org‐clay), were investigated by employing different characterization tools such as X‐ray diffractometer, scanning electron microscope, differential scanning calorimetry, rotational rheometer, dynamic mechanical analysis, and gas permeability measurements. Viscoelastic properties of samples were quantified by applying several test procedures in melt and solid‐state dynamic measurements. It was found that rigid LCP droplets were dispersed well into HDPE matrix and improved the melt elasticity and creep resistance of HDPE. Compatibilizer and org‐clay loading into HDPE/LCP blends yielded formation of smaller LCP droplets and reduced mean relaxation time and shear modulus values, compared to unloaded counterparts. It was observed that org‐clay stacks were dispersed into HDPE phase due to using of maleic anhydride grafted polyethylene as compatibilizer and HDPE/LCP/org‐clay ternary nanocomposites exhibited intercalated microstructure. Solid‐state uniaxial tensile creep behaviors of films were modeled with the Findley power‐law and four‐element Burger models. HDPE/LCP/org‐clay (90/10/5) ternary nanocomposite film exhibited better gas barrier performance than HDPE by decreasing its permeability by 50%. POLYM. ENG. SCI., 59:1344–1353 2019. © 2019 Society of Plastics Engineers     

PE/PE‐g‐MAH/Org‐MMT nanocomposites. II. Nonisothermal crystallization kinetics

The nonisothermal crystallization kinetics of high‐density polyethylene (HDPE) and polyethylene (PE)/PE‐grafted maleic anhydride (PE‐g‐MAH)/organic‐montmorillonite (Org‐MMT) nanocomposite were investigated by differential scanning calorimetry (DSC) at various cooling rates. Avrami analysis modified by Jeziorny, Ozawa analysis, and a method developed by Liu well described the nonisothermal crystallization process of these samples. The difference in the exponent n, m, and a between HDPE and the nanocomposite indicated that nucleation mechanism and dimension of spherulite growth of the nanocomposite were different from that of HDPE to some extent. The values of half‐time (t_1/2), K(T), and F(T) showed that the crystallization rate increased with the increase of cooling rates for HDPE and composite, but the crystallization rate of composite was faster than that of HDPE at a given cooling rate. Moreover, the method proposed by Kissinger was used to evaluate the activation energy of the mentioned samples. It was 223.7 kJ/mol for composite, which was much smaller than that for HDPE (304.6 kJ/mol). Overall, the results indicated that the addition of Org‐MMT and PE‐g‐MAH could accelerate the overall nonisothermal crystallization process of PE. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3054–3059, 2004     

Poly(L‐lactide)/Poly(D‐lactide)/clay nanocomposites: Enhanced dispersion,crystallization, mechanical properties,and hydrolytic degradation

Poly(L ‐lactide) (PLLA)/poly(D ‐lactide) (PDLA)/clay nanocomposites are prepared via simple melt blending method at PDLA loadings from 5 to 20 wt%. Formation of the stereocomplex crystals in the nanocomposites is confirmed by differential scanning calorimetry and wide‐angle X‐ray diffraction (WAXD). The internal structure of the nanocomposites has been established by using WAXD and transmission electron microscope analyses. The dispersion of clay in the PLLA/PDLA/clay nanocomposites can be improved as a result of increased intensity of shear during melt blending. The overall crystallization rates are faster in the PLLA/PDLA/clay nanocomposites than in PLLA/clay nanocomposite and increase with an increase in the PDLA loading up to 10 wt%; however, the crystallization mechanism and crystal structure of these nanocomposites remain unchanged despite the presence of PDLA. The storage modulus has been apparently improved in the PLLA/PDLA/clay nanocomposites with respect to PLLA/clay nanocomposite. Moreover, it is found that the hydrolytic degradation rates have been enhanced obviously in the PLLA/PDLA/clay nanocomposites than in PLLA/clay nanocomposite. POLYM. ENG. SCI., 54:914–924, 2014. © 2013 Society of Plastics Engineers     

Biaxially self‐reinforced high‐density polyethylene prepared by dynamic packing injection molding. I. Processing parameters and mechanical properties

Uniaxial oscillating stress field by dynamic packing injection molding (DPIM) is well established as a means of producing uniaxially self‐reinforced polyethylene and polypropylene. Here, the effects on the mechanical properties of high‐density polyethylene (HDPE) in both flow direction (MD) and transverse direction (TD) of packing modules and processing parameters in DPIM are described. Both biaxially and uniaxially self‐reinforced HDPE samples are obtained by uniaxial shear injection molding. The most remarkable biaxially self‐reinforced HDPE specimens show a 42% increase of the tensile strength in both MD and TD. The difference of stress–strain behavior and impact strength between MD and TD for the DPIM moldings indicates the asymmetry of microstructure in the two directions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1584–1590, 2004     

The morphology and property of HDPE in the presence of oscillation pressure and poly(ethylene terephthalate)

The injection‐molded specimens of neat HDPE and the PET/HDPE blends were prepared by conventional injection molding (CIM) and by pressure vibration injection molding (PVIM), respectively. The effect of oscillation pressure and PET phase with different shapes on superstructure and its crystal orientation distribution of injection molded samples were characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and two‐dimension wide‐angle X‐ray diffraction techniques (2D‐WAXD). Hermans' orientation functions were determined from the wide‐angle X‐ray diffraction patterns. With the PET particles added, the shear viscosity of blend increase and crystallization rate of HDPE phase is enhanced. For the neat HDPE samples, with the promotion from oscillation shear, the orientation parameter experienced a large increase, moreover, the PVIM can induce transverse lamellae (kebabs) twisting in growth direction. Because of the redefined flow field and nucleation effect of PET particles, the crystal orientation of blend is also increased. So the tensile strength of vibration samples enhanced and elongation at break declined. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

动态保压注射成型HDPE/Nano-OMMT复合材料的结构与性能

聚合物/黏土纳米复合材料是近几年聚合物材料改性的热点。为了进一步理解复合材料性能与结构的关系,利用自行研制的动态保压装置,借助WAXD、DSC、SEM等测试方法,研究了高密度聚乙烯(HDPE)/纳米有机蒙脱土(nano-OMMT)复合材料的结构与性能。结果表明,动态保压使OMMT纳米粒子在基体中的分散性提高,并形成插层结构。与此同时,动态剪切力场使HDPE/nano-OMMT复合材料的HDPE基体结构形态亦发生变化,试样中生成串晶结构,相比常规注塑试样,动态保压试样结晶度最大提高15%,结晶形态的变化和结晶度的提高均有利于HDPE/nano-OMMT复合材料强度的提高。力学性能试验显示,拉伸强度和冲击强度同时得到提高,HDPE/nano-OMMT复合试样的拉伸强度最大提高了119%,冲击强度最大提高430%。     

The role of flow‐induced microstructure in rheological behavior and nonisothermal crystallization kinetics of polyethylene/organoclay nanocomposites

The evolution of polyethylene/organoclay nanocomposite microstructure via shear and extentional flow fields was studied by tracing rheological behavior and nonisothermal crystallization kinetics. Although studying microstructure formed through flow fields, two phenomena were noticed: the breaking of three‐dimensional (3D) network containing filler–filler, filler–matrix, and matrix–matrix interactions, and organoclay platelets orientation. Utilizing nonlinear viscoelastic measurements and thermal analyses, it was proven that clay alignment was present only in large enough shear flows and all elongational flows. It was observed that regardless of the type of flow field and its magnitude, due to the breaking of 3D network, the extent of crystallization can be increased. The half‐lives of the crystallization of film samples and those samples subjected to large enough shear rates for clay platelets to be aligned decreased, proving the effect of clay orientation on crystallization rate increment. Based on endotherms observed through melting behavior studies of samples, it was proven that in elongation and large amplitude shear flows, clay orientation had resulted in forming thicker crystalline lamellae, likely because of forcing the adjacent polymer chains to align with the clay platelets. POLYM. ENG. SCI., 54:1839–1847, 2014. © 2013 Society of Plastics Engineers     

Effect of clay addition on the morphology and thermal behavior of polyamide 6

The nanostructure, morphology, and thermal properties of polyamide 6 (PA6)/clay nanocomposites were studied with X‐ray scattering, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The wide‐angle X‐ray diffraction (WAXD) and TEM results indicate that the nanoclay platelets were exfoliated throughout the PA6 matrix. The crystallization behavior of PA6 was significantly influenced by the addition of clay to the polymer matrix. A clay‐induced crystal transformation from the α phase to the γ phase for PA6 was confirmed by WAXD and DSC; that is, the formation of γ‐form crystals was strongly enhanced by the presence of clay. With various clay concentrations, the degree of crystallinity and crystalline morphology (e.g., spherulite size, lamellar thickness, and long period) of PA6 and the nanocomposites changed dramatically, as evidenced by TEM and small‐angle X‐ray scattering results. The thermal behavior of the nanocomposites was investigated with DSC and compared with that of neat PA6. The possible origins of a new clay‐induced endothermic peak at high temperature are discussed, and a model is proposed to explain the complex melting behavior of the PA6/clay nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1191–1199, 2007     

Crystallization and thermal behavior of microcellular injection‐molded polyamide‐6 nanocomposites

This article presents the effects of nanoclay and supercritical nitrogen on the crystallization and thermal behavior of microcellular injection‐molded polyamide‐6 (PA6) nanocomposites with 5 and 7.5 wt% nanoclay. Differential scanning calorimetry (DSC), X‐ray diffractometry (XRD), and polarized optical microscopy (POM) were used to characterize the thermal behavior and crystalline structure. The isothermal and nonisothermal crystallization kinetics of neat resin and its corresponding nanocomposite samples were analyzed using the Avrami and Ozawa equations, respectively. The activation energies determined using the Arrhenius equation for isothermal crystallization and the Kissinger equation for nonisothermal crystallization were comparable. The specimen thickness had a significant influence on the nonisothermal crystallization especially at high scanning rates. Nanocomposites with an optimal amount of nanoclay possessed the highest crystallization rate and a higher level of nucleation activity. The nanoclay increased the magnitude of the activation energy but decreased the overall crystallinity. The dissolved SCF did not alter the crystalline structure significantly. In contrast with conventionally injection‐molded solid counterparts, microcellular neat resin parts and microcellular nanocomposite parts were found to have lower crystallinity in the core and higher crystallinity near the skin. POLYM. ENG. SCI., 46:904–918, 2006. © 2006 Society of Plastics Engineers     

Structure,morphology, and biodegradability of poly(ε‐caprolactone)‐based nanocomposites

Biodegradable polycaprolactone/organoclay nanocomposites were prepared by solvent casting, using different amounts of filler and matrices differing by average molecular weight. Intercalated nanocomposites were obtained. The nanocomposites were characterized by wide‐angle X‐ray diffraction (WAXD) and small‐angle X‐ray scattering (SAXS) methods. Negligible variations in the degree of crystallinity were detected by WAXD. The thickness of crystalline lamellae, measured by SAXS, increased in low molecular weight polymer nanocomposites with increasing clay amount; this effect was weakened in matrices with high molecular weight. Differential scanning calorimetry showed an inhibiting effect of clay on crystallization. The composites' ductility was largely increased, whereas stiffness was retained. After biodegradation in compost, in all samples, the degree of crystallinity was increased, meaning that the less ordered portion of the sample was preferentially degraded. Clay slowed down the biodegradation rate, coherently with the observed increase in the lamellar thickness due to the filler. This may offer a strategy for tuning the biodegradability by calibrating their semicrystalline framework. POLYM. ENG. SCI., 2011. ©2011 Society of Plastics Engineers.     

Effects of clay and POSS nanoparticles on the quiescent and shear‐induced crystallization behavior of high molecular weight poly(ethylene terephthalate)

The effects of organoclay and polyhedral oligomeric silsesquioxanes (POSS) nanoparticles on the crystallization behavior of high molecular weight poly(ethylene terephthalate) (HMWPET; inherent viscosity of 1.05) were investigated in terms of nanoparticle content and shear rate. Both nanoparticles played a role of nucleating agent for PET and increased the cold crystallization temperature by about 24°C. The half‐time of crystallization was also decreased with increasing the nanoparticle content. Clay proved to be more effective than POSS; a notable nucleating effect was observed at 0.3 wt% for clay and 2 wt% for POSS. Introducing 1 wt% of clay gave the highest crystallization rate among all PET nanocomposite samples examined. Isothermal crystallization of the nanocomposites under dynamic shear exhibited similar crystallization behavior. As in the DSC measurement, clay appeared to be more effective to promote the crystallization of PET under shear. The nucleating effects were more noticeable at higher shear rate. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Nonisothermal crystallization of high density polyethylene and nanoscale calcium carbonate composites

Nonisothermal crystallization of high density polyethylene (HDPE)/maleic anhydride‐modified HDPE(manPE)/nanoscale calcium carbonate (CaCO₃) nanocomposite was investigated by means of wide angle X‐ray diffraction (WAXD), polarized optical microscopy (POM), and differential scanning calorimetry (DSC). WAXD indicated that the crystallinity was reduced with the addition of CaCO₃. The spherulite size of HDPE increased in the presence of manPE, but decreased when CaCO₃ was added from observation of POM. A modified Avrami analysis, Ozawa analysis, and Liu analysis were applied to the nonisothermal crystallization process. Crystallizability followed the order: HDPE/manPE/CaCO₃ > HDPE/CaCO₃ > HDPE/manPE > HDPE when undercooling was taken into account. Dependence of the effective activation energy on the relative crystallinity was estimated by the Friedman equation, and the results were used to calculate the parameters (K_g and U*) of Lauritzen‐Hoffman's equation by Vyazovkin's method. These results indicate that the addition of maleic anhydride groups and CaCO₃ tend to promote the nucleation of spherulites on their surfaces and lead to epitaxial growth of the crystallites. But at the same time, manPE and CaCO₃ particles may hinder the transport of the molecule chains resulting in a decrease of the crystallization growth rate. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Thermal and wide angle X‐ray analysis of chemically and radiation‐crosslinked low and high density polyethylenes

Low and high density polyethylenes (PE) were crosslinked by two methods, namely, chemically by use of different amounts of tert‐butyl cumyl peroxide (BCUP) and by irradiation with different doses of electron beam. A comparison between the effects of these two types of crosslinking on crystalline structure, crystallinity, crystallization, and melting behaviors of PE was made by wide angle X‐ray diffraction and DSC techniques. Analysis of the DSC first heating cycle revealed that the chemically induced crosslinking, which took place at melt state, hindered the crystallization process and decreased the degree of crystallinity, as well as the size of crystals. Although the radiation‐induced crosslinking, which took place at solid state, had no significant influence on crystalline region, rather, it only increased the melting temperature to some extent. However, during DSC cooling cycle, the crystallization temperature showed a prominent decrease with increasing irradiation dose. The wide angle X‐ray scattering analysis supported these findings. The crystallinity and crystallite size of chemically crosslinked PE decreased with increasing peroxide content, whereas the irradiation‐crosslinked PE did not show any change in these parameters. As compared with HDPE, LDPE was more prone to crosslinking (more gel content) owing to the presence of tertiary carbon atoms and branching as well as owing to its being more amorphous in nature. HDPE, with its higher crystalline content, showed relatively less tendency toward crosslinking especially by way of irradiation at solid state. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3264–3271, 2006     

Crystallization behavior of syndiotactic polystyrene nanocomposites for melt‐ and cold‐crystallizations

Analyses of the effects of montmorillonite (clay) on the crystallinity and crystallization behavior of syndiotactic polystyrene (s‐PS) were investigated by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The dispersibility of the clay in s‐PS nanocomposites was studied by X‐ray and transmission electron microscopy (TEM). The clay was dispersed into the s‐PS matrix by melt blending on a scale of 1–2 nm or few tenths–100 nm, depending on the surfactant treatment. On adding clay, the crystallization behavior of the s‐PS tends to convert into the β‐crystal from the α‐crystal after being cold‐crystallized because the clay plays a vital role in facilitating the formation of the thermodynamically favored β‐form crystal when the s‐PS is cold‐ or melt‐crystallized. This phenomenon leads to a change in a conventional mechanism of molecular packing for the s‐PS. Evidently, the clay significantly affects the crystallinity and crystallization behavior of the s‐PS. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2492–2501, 2002