Devulcanized ground tire rubber (DGTR) samples were produced using an independently developed industrially sized single-screw extruder. The DGTR was further revulcanized to produce revulcanized DGTR (RDGTR) samples. The structure and properties of the produced samples were investigated via tests and characterization of sol fraction, crosslink density, Fourier transform infrared spectroscopy spectra, X-ray photoelectron spectroscopy spectra, Mooney viscosity, curing characteristics, dynamic rheology, tensile properties, and surface morphology. The results demonstrate that the extruder can effectively break up crosslinked structure of ground tire rubber to achieve high devulcanization level (characterized by sol fraction and crosslink density), which is mainly associated with its moderate shear strength. The balance between mechanical properties and processability for the DGTR samples was analyzed. Lower ratios of main-chain to crosslink scission and good processability (mainly characterized by modest Mooney viscosity) for the DGTR samples, and high tensile strengths and elongations at break for the RDGTR samples are obtained via appropriately combining the barrel temperature and screw speed. High quality DGTR sample with tensile strength and elongations at break of up to 11 MPa and 370%, respectively, is prepared under the conditions used in this work. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43761.

This work focuses on largely toughening poly(lactic acid)/thermoplastic polyurethane (PLA/TPU) blend with lower content (20 wt %) of TPU using appropriate contents of 4,4-methylene diphenyl diisocyanate (MDI) via simple melt blending. Both scanning electron micrographs and differential scanning calorimetry curves suggest little change of the compatibility between the PLA and TPU phases by adding the MDI. Dynamic rheological test demonstrates that a reaction occurs between the TPU phase and MDI during melt blending. Combining the rheological behaviors and gel contents of the blends, it can be speculated that adding the MDI extends the TPU chains and forms branched and crosslinked structure in the TPU chains sequentially. Toughening mechanism is analyzed and different impact strengths for the blends with different MDI contents are explained based on combined effects of the decreased crystallinities for the PLA matrix and the extended, branched and crosslinked structure in the TPU chains. A 0.8 wt % MDI content is optimal in terms of the impact strength (100.6 kJ/m²) and the elongation at break (392.4%). The former is about 1.9 and 32.5 times of that for the blend without MDI and the PLA, respectively. Moreover, the MDI results in some increase in the tensile strength of the blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42511.

Polymer melts exhibit unique rheological behaviors at high shear rate up to 10⁶ s⁻¹, which is a common phenomenon in micro-injection molding. Both online and commercial capillary rheometers, which were modified to allow regulation of back pressure, were used for measuring the melt shear viscosities of polystyrene (PS), polypropylene (PP), and linear low-density polyethylene (LLDPE) under high shear rates. The rheological characteristics of the three melts were compared through the systematical analyses for three significant effects, namely the end pressure loss, pressure dependence, and dissipative heating in capillary flow. Pronounced end effect begins to appear at the shear rates of 1.6 × 10⁵, 8.0 × 10⁵, and 2.8 × 10⁶ s⁻¹ for the PS, PP, and LLDPE melts, respectively. The significance of the end effect can be ordered as PS > PP > LLDPE. It seems that the polymers with more complex molecular structures exhibit a higher degree of divergence between the comprehensively corrected and uncorrected melt viscosity curves. Moreover, the dissipation effect begins to predominate over the pressure effect under the lowest shear rate of 10⁵ s⁻¹ for the PS melt among the three melts. POLYM. ENG. SCI., 55:506–512, 2015. © 2014 Society of Plastics Engineers

By adding a polymeric β-nucleating agent (acrylonitrile–styrene copolymer, SAN), in situ microfibril reinforced isotactic polypropylene (iPP)/SAN blend parts with high contents of β-form crystals and transcrystals were molded via water-assisted injection molding (WAIM). Thanks to the unique stress and temperature fields occurring during the WAIM, SAN microfibers formed across the whole residual wall of iPP/SAN blend parts with relatively large thickness. Numerical simulations on high-pressure water penetration and cooling stages of the WAIM were carried out to reveal the stress and temperature fields. Comprehensive analysis of both experimental and simulated results showed that not only the shear flow field but also elongational flow field occurring during the WAIM was responsible for the formation of SAN microfibers and unique crystal morphology distribution in the WAIM iPP/SAN blend part. Moreover, during the WAIM, the high cooling rate also played an important role in the formation of both phase and crystal morphologies. The preferential formation of transcrystals in the inner layer of WAIM iPP/SAN blend part could be ascribed to the strong elongation, rather than the strong shear. It was believed that the quantification of stress and temperature fields of the WAIM via numerical simulation could provide a guidence for molding high-performance products. POLYM. ENG. SCI., 55:1698–1705, 2015. © 2014 Society of Plastics Engineers

The relaxation behaviors of the binary immiscible blends reflected on the plots of the storage modulus and the imaginary part of complex viscosity were investigated using the Maxwell and the Palierne models. It was revealed that the peaks in the high- and low-frequency regions on the complex viscosity imaginary part plot are owing to the relaxations of the blend and deformed dispersed droplets, respectively. Based on these two models, six emulsion parameters (interfacial tension, relaxation times and viscosities of two components, and dispersed phase volume fraction) were investigated in terms of their effects on the shape features of the plots of the imaginary part of complex viscosity and the Cole–Cole. The results showed that the viscosities of two components and dispersed phase volume fraction play key roles in the radii of the two circular arcs on the Cole–Cole plot. Furthermore, the two circular arcs are well separated in the case of lower interfacial tensions and dispersed phase viscosities, shorter matrix relaxation times, and higher matrix viscosities and dispersed phase volume fractions. The total relaxation time of the deformed dispersed droplets increases with increasing the viscosities of two components, especially with decreasing the interfacial tension. Three types of polymer blends were prepared and their dynamic frequency sweep testing results demonstrated the effectiveness of the corresponding predicted results. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39690.

An optimization design method is developed for the electric heating system in rapid thermal cycling molding (RTCM) mold. First, a multiobjective optimization model is established, in which the distance between the mold cavity surface and the center of heating elements and the number and power density of heating elements are the design variables, the required heating time t_h and the highest cavity surface temperature T_max at time t_h are the objective functions. Then, an optimization strategy consisting of design of experiment, finite element analysis, artificial neural network (ANN) and response surface methodology (RSM) models, and Pareto-based genetic algorithm is proposed to solve the multiobjective optimization model. Finally, the optimization strategy is applied for the design of the heating system for an automotive spoiler blow mold. The results show that the temperature distribution uniformity on the blow mold cavity surface is obviously improved and high heating efficiency is also ensured with the optimized design parameters. Moreover, the ANN model exhibits its superiority over the RSM model in terms of modeling and predictive abilities. A RTCM blow mold with the optimized electric heating system is constructed and successfully utilized to mold high gloss automotive spoiler. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 39976.

A novel technology, being called as microcellular injection-compression molding (MICM), was proposed for the first time to search an effective way for improving the cellular structure of foamed parts. Both MICM and standard microcellular injection molding (MIM) were used to mold rectangular foamed polystyrene plates with the thicknesses of 5, 4, and 3 mm. Compared to the MIM samples, the MICM samples exhibited thinner outer zone, in which irregular striation-shaped cells were dominated, at three positions along the sample axis; the MICM samples exhibited a little more uniform cellular shape and size distribution in the outer zone, and more uniform cellular structure with smaller sizes in the inner zone, being dominated by ellipsoidal cells, at three positions. Improved cellular structure in the MICM sample leads to its higher storage modulus in the glassy state. Based on the cellular structure in the samples with the three thicknesses, a cellular development mechanism in the compression stage during MICM was proposed and analyzed thoroughly. Moreover, using the MICM can lower the maximum cavity pressure by about 18.6, 29.3, and 55.6% for 3, 4, and 5-mm-thick samples, respectively. POLYM. ENG. SCI., 54:327–335, 2014. © 2013 Society of Plastics Engineers

Microinjection-compression molding was used to fabricate isotactic polypropylene part with microscale thickness. The combined effect of shear (up to the order of 10⁵ s⁻¹) and elongational deformations imposed by the Poiseuille (injection stage) and squeeze (compression stage) flow resulted in pronounced flow-induced crystallization under rapid quenching. Hierarchical crystalline morphology, characterized by two oriented layers, a transitional layer in between, and an isotropic core layer, was detected through the thickness in the upstream region initially filled in injection stage, whereas skin-core morphology appeared in the downstream region filled in subsequent compression stage. Under the molding conditions imposing sufficient strain rates, predominant shish-kebabs developed in the oriented layer. Furthermore, the oriented layer thicknesses, crystallinity, β-form content, and melting behavior of molded parts, all of which were closely correlated with the calculated strain rates, as well as the location of inner oriented layer could be manipulated via varying the compression-related parameters. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

During micro-injection molding, the polymer melt may undergo a shear rate up to 10⁶ s⁻¹, at which the rheological behaviors are obviously different from those in conventional molding process. Using both online and commercial rheometers, high-shear-rate capillary rheology of polystyrene (PS) melt is analyzed systematically in this work. The accurate end pressure drop and pressure coefficient of viscosity are determined via the enhanced exit pressure technique. Experimental and theoretical investigations are conducted on four significant effects, that is, the dissipative heating, end pressure loss, pressure dependence, and melt compressibility in capillary flow. For the PS melt, which exhibits distinct temperature and pressure dependence of viscosity, both dissipation and end effects become pronounced as the shear rate exceeds 2 × 10⁵ s⁻¹. From lower to higher shear rates (10³–10⁶ s⁻¹), the competition between dissipation and pressure effects results in the overestimation to underestimation of Bagley-corrected pressure drop, and finally the comprehensively corrected viscosity becomes about half of the uncorrected one owing to the enhanced superimposed effects. Moreover, the compressibility shows a minor influence on the shear viscosity. Under the shear rate range investigated, the power-law relationship is sufficient for describing the corrected viscosity curve of PS melt used. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

The melt temperature and a special polymeric nucleating agent [acrylonitrile–styrene copolymer (SAN)] were investigated to find an effective way for tailoring the crystalline structures of the water-assisted injection-molded polypropylene (WAIM PP) parts. The results showed that lowering the melt temperature led to the formation of a small amount of β-form crystals in both outer and core layers of the WAIM PP parts. Nevertheless, the melt temperature had little effect on tailoring the crystalline structures of the WAIM PP parts. The addition of a low content (6 wt%) of the SAN was interestingly found to gradually influence the crystalline structures as lowering the melt temperature. WAIM PP/SAN blend parts with high contents of β-form in both outer and core layers (30.7 and 18.4%, respectively), and high contents of transcrystals in the inner layer were molded at relatively low melt temperature (180°C), whereas the SAN had little influence on the crystalline structures at higher melt temperature (230°C). The formation of the transcrystals was ascribed to the in situ fibrillation of the SAN, which was resulted from high shear and cooling rates caused by high-pressure water penetration during WAIM. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers

The biomass-based blend of 80/20 (w/w) poly(lactic acid)/poly(butylene succinate) (PLA/PBS) is prepared using an extruder. The prepared blend shows a typical droplet-matrix morphology. The relaxation behavior of the blend is investigated in terms of storage modulus, loss tangent, and Cole–Cole plots. In the low frequency region, the blend exhibits higher elastic indices than the pure components on the storage modulus and loss tangent curves, and remarkable deviation from a semicircular shape on the Cole–Cole plot. These features are thought to arise from the relaxation of the deformed droplets. The loss tangent curve is more sensitive to the relaxation behavior of the deformed droplets than the storage modulus curve. Moreover, the complex viscosity of the blend is separated into real and imaginary parts to further analyze its relaxation behavior. Three relaxation times for the blend are defined on the curve of the imaginary part of the viscosity. It is demonstrated that the reciprocal of the frequency corresponding to the peak in the low frequency region on the imaginary part curve is equal to the longest relaxation time of the blend obtained from the storage modulus curve. Based on this result, a new method is proposed to calculate the interfacial tension between the PLA and PBS in the blend, which is 3.7 mN/m. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The LLDPE/HDPE blends with two different weight ratios as well as pure LLDPE were molded by means of water-assisted and conventional injection molding (WAIM and CIM) in terms of their different thermal fields. The formation of the crystal morphology in the molded parts was investigated by a scanning electron microscope. The results showed that banded spherulites formed in the WAIM and CIM pure LLDPE parts. Banded spherulites of LLDPE coexisted with the randomly oriented lamellae of HDPE for LLDPE/HDPE blend parts with lower HDPE content at higher cooling rates, whereas a banding to nonbanding morphological transition occurred for LLDPE component (particularly for blend with higher HDPE content) at lower cooling rates. The heterogeneous nucleation effect of HDPE component on LLDPE component was responsible for the banding to nonbanding morphological transition by hindering the twist of LLDPE lamellae. It was interesting to find that the thermal effect, rather than the shear effect, was the main factor for the formation of crystal morphologies in both CIM and WAIM blend parts. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Both 80/20 and 60/40 polypropylene/poly(ethylene-co-octene) (PP/POE) blend samples were collected from four positions along a single-screw extruder, which can induce chaotic and shear mixing, respectively. Results indicated that a wide range of impact strengths was obtained as the formation of series of phase morphologies. For the 80/20 blends, the impact strength increased gradually along the extruder with shear mixing due to gradual decrease of both diameter and size distribution coefficient of droplets. Whereas the impact strengths reached the highest value at about 2/3 length of the whole screw with chaotic mixing as the formation of lamellas, then decreased as their breakup. For the 60/40 blends, the impact strength reached the highest value as the formation of the thick fibrils with shear mixing; whereas the impact strength became higher at about 2/3 length of the whole screw as the formation of thin fibrils and the highest (69 times of that of pure PP) at the end of the screw due to the formation of cocontinuous structure with chaotic mixing. Observing the fractured surface of the tested sample with cocontinuous structure revealed that a distinct deformation of the PP matrix was induced by the shear yielding during impact testing. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

By using supercritical carbon dioxide (sc-CO₂) as the physical foaming agent, microcellular foaming was carried out in a batch process from a wide range of immiscible polypropylene/polystyrene (PP/PS) blends with 10–70 wt% PS. The blends were prepared via melt processing in a twin-screw extruder. The cell structure, cell size, and cell density of foamed PP/PS blends were investigated and explained by combining the blend phase morphology and morphological parameters with the foaming principle. It was demonstrated that all PP/PS blends exhibit much dramatically improved foamability than the PP, and significantly decreased cell size and obviously increased cell density than the PS. Moreover, the cell structure can be tunable via changing the blend composition. Foamed PP/PS blends with up to 30 wt% PS exhibit a closed-cell structure. Among them, foamed PP/PS 90:10 and 80:20 blends have very small mean cell diameter (0.4 and 0.7 µm) and high cell density (8.3 × 10¹¹ and 6.4 × 10¹¹ cells/cm³). Both of blends exhibit nonuniform cell structure, in which most of small cells spread as “a string of beads.” Foamed PP/PS 70:30 blend shows the most uniform cell structure. Increase in the PS content to 50 wt% and especially 70 wt% transforms it to an irregular open-cell structure. The cell structure of foamed PP/PS blends is strongly related to the blend phase morphology and the solubility of CO₂ in PP more than that in PS, which makes the PP serve as a CO₂ reservoir. Copyright © 2009 John Wiley & Sons, Ltd.

The melt blending of polylactide (PLA) and thermoplastic polyurethane (TPU) elastomer was performed in an effort to toughen the PLA. The phase morphology, mechanical properties, and toughening mechanism of the PLA/TPU blends were investigated. The results indicate that the spherical TPU particles dispersed in the PLA matrix, and the uniformity decreased with increasing TPU content. There existed long threads among some TPU droplets in blend with 30 wt % TPU. TPU improved the toughness of the PLA. With 30 wt % TPU, the elongation at break of the blend reached 602.5%, and samples could not be broken in the notched Izod impact tests at room temperature. The matrix ligament thickness of the PLA/TPU blends was below the critical value, and the blends deformed to a large extent because of shear yield caused by debonding, the formation of fibers upon impact; this dissipated a large amount of energy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Injection-compression molding (ICM) has received increased attention because of its advantages over conventional injection molding (CIM). This article aims to investigate the effects of five dominating ICM processing parameters on fiber orientation in short-fiber-reinforced polypropylene (SFR-PP) parts. A five-layer structure of fiber orientation is found across the thickness under most conditions in ICM parts. This is quite different from the fiber orientation patterns in CIM parts. The fibers orient orderly along the flow direction in the shell region, whereas most fibers arrange randomly in the skin and the core regions. Additionally, the fiber orientation changes in the width direction, with most fibers arranging orderly along the flow direction at positions near the mold cavity wall. The results also show that the compression force, compression distance, and compression speed play important roles in determining the fiber states. Thicker shell regions, in which most fibers orient remarkably along the flow direction, can be obtained under larger compression force or compression speed. Moreover, the delay time has an obvious effect on the fiber orientation at positions far from the gate. However, the effect of compression time is found to be negligible. POLYM. COMPOS., 31:1899–1908, 2010. © 2010 Society of Plastics Engineers.

High-density polyethylene (HDPE)–wood composite samples were prepared using a twin-screw extruder. Improved filler–filler interaction was achieved by increasing the wood content, whereas improved polymer–filler interaction was obtained by adding the compatibilizer and increasing the melt index of HDPE, respectively. Then, effects of filler–filler and polymer–filler interactions on dynamic rheological and mechanical properties of the composites were investigated. The results demonstrated that enhanced filler–filler interaction induced the agglomeration of wood particles, which increased the storage modulus and complex viscosity of composites and decreased their tensile strength, elongation at break, and notched impact strength because of the stress concentration. Stronger polymer–filler interaction resulted in higher storage modulus and complex viscosity and increased the tensile and impact strengths due to good stress transfer. The main reasons for the results were analyzed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Polypropylene/nano-calcium carbonate (PP/nano-CaCO₃) composites were prepared by using an intermeshing, co-rotating twin-screw extruder. Two different screw configurations, denoted by screws A and B, respectively, were employed. The former provided high dispersive mixing and the later provided high dispersive and distributive mixing. Effect of mixing type on microstructure and rheologic development of nanocomposites was investigated by taking samples from four locations along screws A and B. Transmission electron microscopy results show that in the sample at the exit of extruder, the percentage of nano-CaCO₃ particles with the equivalent diameter lower than 100 nm along screws A and B is 66.5 and 79.0%. respectively. Moreover, for screw B, the number-averaged diameter at four sampling locations is smaller than that for screw A. This means that the distributive mixing, provided by screw B, favors the size decrease of nano-CaCO₃ in the PP matrix. In addition, rheologic results show that the decrease of complex viscosity for the nanocomposites is deeply related to turbine mixing elements, which provides distributive mixing. The online melt shear viscosity of the nanocomposite at the exit of extruder prepared by screw B is lower than that of pure PP. This is related to the dispersion of nano-CaCO₃ in PP matrix. Finally, the relationship between rheologic properties and microstructure was analyzed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Experiments of water-assisted injection molded polypropylene curved pipe were carried out on newly developed equipment in this lab. First, four processing parameters, including short-shot size, melt temperature, water injection delay time, and water pressure, were investigated in terms of their effects on the water penetration length and residual wall thickness of curved pipe. Second, an orthogonal array of Taguchi, the S/N ratio, and ANOVA were utilized to find the optimal processing parameters resulting in maximum water penetration length. Finally, the crystallization behavior difference between the beginning and the end of the water channel of the curved pipe was analyzed using differential scanning calorimetry. It was interesting to find that the crystallinity of sample from the middle is higher than those from both outer and inner layers at position near the water inlet. The samples taken from the outer layer, middle, and inner layer show similar melting peak and crystallinity at position near the end of water channel. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008