Evaluation of dynamic elastic properties of wood‐filled polypropylene composites

Dynamic modulus of elasticity (MoE) and shear modulus of wood‐filled polypropylene composite at various filler contents ranging from 10% to 50% was determined from the vibration frequencies of disc‐shaped specimens. Wood filler was used in both fiber form (pulp) and powder form (wood flour). A novel compatibilizer, m‐isopropenyl‐α,α‐dimethylbenzyl‐isocyanate(m‐TMI) grafted polypropylene with isocyanate functional group was used to prepare the composites. A linear increase in dynamic MoE, shear modulus, and density of the composite was observed with the increasing filler content. Between the two fillers, wood fiber filled composites exhibited slightly better properties. At 50% filler loading, dynamic MoE of the wood fiber filled composite was 97% higher than that of unfilled polypropylene. Halpin‐Tsai model equation was used to describe the changes in the composite modulus with the increasing filler content. The continuous improvement in elastic properties of the composites with the increasing wood filler is attributed to the effective reinforcement of low‐modulus polypropylene matrix with the high‐modulus wood filler. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1706–1711, 2006     

Fatigue performance of an injection molded talc‐filled polypropylene

This paper reports the fatigue behavior of an injection molded 40wt% talc‐filled polypropylene. The effects of specimen orientation relative to the flow direction, weld line, hole stress concentration and test frequency on the fatigue performance of this material have been considered. The fatigue strength in the flow direction was higher than that normal to the flow direction. However the orientation effect decreased at lower fatigue stress level. The presence of weld line reduced the fatigue strength. On the other hand, the fatigue strength showed very little sensitivity to the presence of hole stress concentration. The failure mode in fatigue was influenced by the test frequency. When the test frequency was less than or equal to 2 Hz, the failure mode of the talc‐filled polypropylene was due to fatigue and the fatigue life increased with frequency. However, when the test frequency was greater than or equal to 5 Hz, the failure of the talc‐filled polypropylene was due to thermal softening and the fatigue life did not appear to be influenced much by the frequency. POLYM. ENG. SCI., 45:510–516, 2005. © 2005 Society of Plastics Engineers     

Injection molding and injection compression molding of thin‐walled light‐guided plates with V‐grooved microfeatures

In this study, we investigated the feasibility of injection molding (IM) and injection compression molding (ICM) for fabricating 3.5‐in. light‐guided plates (LGPs). The LGP was 0.4 mm thick with v‐grooved microfeatures (10 μm wide and 5 μm deep). A mold was designed to fabricate LGPs by IM and ICM. Micromachining was used to make the mold insert. The Taguchi method and parametric analysis were applied to examine the effects of the process parameters on the molding quality. The following parameters were considered: barrel temperature, mold temperature, packing pressure, and packing time. Mold temperature in this investigation was in the conventional range. Increasing the barrel temperature and mold temperature generally improved the polymer melt fill in the cavities with microdimensions. The experimental results for the replication of microfeatures by IM and ICM are presented and compared. The height of the v‐grooved microfeatures replicated by ICM was more accurate than those replicated by IM. Additionally, the flatness of the fabricated LGPs showed that ICM was better than IM for thin‐walled molding. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fungal degradation of wood‐plastic composites and evaluation using dynamic mechanical analysis

Small samples of two wood–polyethylene (HDPE) composite formulations were incubated with either the white‐rot fungus Trametes versicolor or the brown‐rot fungus Gloeophyllum trabeum for 24 and 77 days in an agar‐block test. Noninoculated, side‐matched controls were employed in the tests to serve as references, and solid wood samples of yellow‐poplar (Liriodendron tulipifera L.) inoculated with T. versicolor were included as positive controls. Potential changes in storage and loss moduli because of fungal colonization and moisture were determined using dynamic mechanical analysis, whereas weight loss and visual observation served as indicators of fungal decay. Severe losses in storage modulus (E′) and loss modulus (E″) following incubation of yellow‐poplar with T. versicolor were observed. However, the E′ of the two wood–plastic composite (WPC) formulations increased after 24 days of incubation with T. versicolor. The same effect was observed for G. trabeum, but only in one formulation. The increase of E′ was attributed to a reinforcing effect of the fungal hyphae present in the interfacial gaps between the wood filler and the polymer matrix. Dynamic temperature scans revealed a peak in E″ between 30°C and 63°C, depending on the frequency and fungal treatment. The peak temperature of E″ represents the α‐transition of HDPE. Increased activation energies were required for the α‐transition in WPC samples incubated with T. versicolor for 77 days as compared to controls. This observation confirmed that incubation of WPC with T. versicolor improved interfacial adhesion and reinforced the composite under the assay conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3138–3146, 2006     

Shear‐induced crystallization of injection molded vetiver grass‐polypropylene composites

Vetiver grass was used as an alternative filler in polypropylene (PP) composites in this study. Chemical treatment of vetiver grass by alkalization was carried out to obtain alkali‐treated vetiver grass. It was shown that alkali‐treated vetiver grass exhibited higher thermal stability than untreated vetiver grass. Injection molding was used to prepare the composites. The microstructure of injection molded samples showed a distinct skin layer due to shear‐induced crystallization. It was found that normalized thickness of shear‐induced crystallization layer of the composite was lower than that of neat PP. The effect of vetiver particle sizes on shear‐induced crystallization and physical properties of the composites were elucidated. Furthermore, the effect of processing conditions on shear‐induced crystallization, degree of crystallinity, gapwise crystallinity distribution, and mechanical properties of the composite were investigated. It was shown that injection speed and mold temperature affected the normalized thickness of shear‐induced crystallization layer and degree of crystallinity of the composites. However, processing conditions showed insignificant effect on the mechanical properties of vetiver fiber‐PP composites. The degree of crystallinity showed no distribution throughout the thickness direction of the composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Graft copolymers of lignin as hydrophobic agents for plastic (wood‐filled) composites

Poly[lignin‐g‐(1‐phenylethylene)] graft copolymers synthesized by free‐radical, graft copolymerization on lignin and verified by fractionation, infrared spectroscopy, and solubility change possess macromolecular surface activity as indicated by their capacity to form stable emulsions between incompatible fluid phases, to adhesively bond to wood surfaces, and to change the contact angle of water on coated wood. The surface activity of the copolymer changes with its composition. As the weight percent lignin in the copolymerization reaction product increases beyond 20 wt %, the amount of the emulsion phase formed in a water–benzene mixture decreases. Maple wood flour could be solvent‐coated with a copolymer and both coated and uncoated maple flour could be extruded through a stranding plate into a wood‐filled composite with polystyrene. Physical property tests show that composite control samples are about 3% stiffer and less deformable than are the copolymer composites when dry and about 5 or more percent more deformable than are the copolymer composites when wet, showing that the copolymer coating increased the wet strength. The copolymer samples are always denser than are the controls. Copolymer coating on wood filler decreases the swelling in the composite, the partial molar volume of the imbibed water, and the dimensional change in the solid. These effects cause increase in the density of the copolymer composite upon imbibition of water. Coating the wood component of the composite with a copolymer creates a hydrophobic barrier that produces a decrease in water imbibition into the composite, which will not disappear in 20 or more years of water immersion. Expansion in water is highly dependent on the direction of extrusion. The length expands about 1%, the width expands about five times as much, and the thickness expands over 10 times as much as does the length. This differential expansion may be due to the 22% reduction in the width and a 71% reduction in the thickness of the melt as it passes through the die and the alignment of the long axis of the fiber with the direction of flow through the die. The reaction product is a thermoplastic solid stable below 200°C and thermoformable at between 150 and 180°C. Products which contain between 10 and 50 wt % lignin are heterogeneous solids. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1266–1276, 2003     

Thermal and mechanical properties of wood‐plastic composites filled with multiwalled carbon nanotubes

Wood plastic composites (WPCs) are a new generation of green composites which can come mostly from recycled materials. This study focuses on the thermal conductivity and mechanical properties of WPCs filled multiwalled carbon nanotubes (MWCNTs). The thermal conductivity increases with increasing amount of MWCNTs and decreases with increasing temperature. By comparing the temperature changes of specimens during heating and cooling processes, WPCs with higher MWCNTs contents presents higher average temperature when heated until equilibrium temperature. From differential scanning calorimeter test, the melting temperatures of MWNTs reinforced WPCs change slightly, but the crystallinity is reduced with the increasing amount of MWCNTs. Based on a series of laboratory experiments carried out to investigate the mechanical performance, it can be concluded that the addition of the MWCNTs decreases the mechanical properties of WPCs due to the decohesion between thermoplastic matrix and MWCNTs particles under stress. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46308.     

Hygrothermal aging and tensile behavior of injection‐molded rice husk‐filled polypropylene composites

The effect of the filler volume fraction on the tensile behavior of injection‐molded rice husk‐filled polypropylene (RH–PP) composites was studied. Hygrothermal aging behavior was also investigated by immersing the specimens in distilled water at 30 and 90°C. The kinetics of moisture absorption was studied from the amount of water uptake by specimens at regular interval times. It was found that the diffusion coefficient and the maximum moisture content are dependent on the filler volume fraction and the immersion temperatures. Incorporation of RH into the PP matrix has led to a significant improvement in the tensile modulus and a moderate improvement in the tensile strength. Elongation at break and energy at break, on the other hand, decreased drastically with the incorporation of the RH filler. The extent of deterioration incurred by hygrothermal aging was dependent on the immersion temperature. Both the tensile strength and tensile modulus deteriorated as a result of the combined effect of thermal aging and moisture attack. Furthermore, the tensile properties were not recovered upon redrying of the specimens. Scanning electron microscopy was used to investigate the mode of failure of the RH–PP composites. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 742–753, 2001     

Modeling material property heterogeneity in fiber‐reinforced injection molded plastic parts

Fiber reinforced plastic parts manufactured by injection molding have heterogeneous stiffness and strength behavior due to the molding process influence on the fiber orientations. This paper presents a methodology for determining the process‐dependent anisotropic and inhomogeneous mechanical properties of injection‐molded parts using a thickness‐wise layered homogenization technique. This technique produces an equivalent laminated meso‐scale representation at any location in the part and enables point‐wise application of the existing laminated plate and shell theories. The methodology is demonstrated by illustrating property variations in edge‐gated and center‐gated plaques. Spatial variations of elastic moduli, shear modulus, and Poisson's ratio are modeled. The model can be conveniently embedded within finite element structural analyses accounting for the process‐dependent material heterogeneities within the structure. POLYM. COMPOS., 26:98–113, 2005. © 2004 Society of Plastics Engineers     

Dynamic crystallization of polypropylene and wood‐based composites

Thermoplastic composites made of an isotactic polypropylene (iPP) matrix and woodflour (WF) were prepared by melt‐blending, using twin‐screw extrusion and injection molding. Up to 20 wt % of the composite was composed of WF. The incorporation of an interfacial agent made of an ethylene/methacrylic acid copolymer to iPP and WF, PP/WF, binary blends causes a compatibilization effect that becomes evident due to a reduction in the crystallization temperature of PP. In both the binary composites and the compatibilized or ternary composites, the PP adopts an α or monoclinic structure when crystallization occurs from the melt under dynamic conditions at cooling rates between 1 and 20°C min^?1. On the other hand, X‐ray diffraction analysis using synchrotron radiation of the injection‐molded samples demonstrates the existence of a β or trigonal form in the binary as well as the ternary PP/WF composites. They reach k_β levels between 0.18 and 0.25, which can be interpreted as the co‐operation between a reduction of the crystallization rate and the shear effect induced during the injection. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 6028–6036, 2006     

Shrinkage and warpage prediction of injection‐molded thin‐wall parts using artificial neural networks

This study demonstrates the successful use of back‐propagation artificial neural networks (BPANNs) in predicting the shrinkage and warpage of injection‐molded thin‐wall parts. The effects of structural parameters of a BPANN on the predictionaccuracy and the capability of a BPANN in determining the optimal process condition are also discussed. The training and testing data are obtained experimentally based on a Taguchi L₂₇ (3¹³) test schedule. The results show that the trained BPANN can successfully predict the shrinkage and warpage of injection‐molded thin‐wall parts. Comparing the prediction accuracies of the trained BPANN and C‐Mold software, it is noted that the trained BPANN predicts more accurately. In terms of determining the optimal process condition for minimizing the shrinkage and warpage of injected thin‐wall parts, the trained BPANN is also shown to give a better optimal process condition than Taguchi's method. Polym. Eng. Sci. 44:2029–2040, 2004. © 2004 Society of Plastics Engineers.     

薄壁塑件注塑压缩成型多指标工艺参数的优化

基于Minitab软件建立6因素5水平的田口试验并与模糊数学中的综合评判法相结合,以电脑显示器外壳为研究对象,对不同工艺条件下的注塑压缩成型过程进行模拟分析,对塑件成型后的最大翘曲变形量、平均熔接线和平均体积收缩率等3个目标值进行综合评判。通过对综合评分进行极差分析,确定了模具温度、熔体温度、压缩力、压缩速度、压缩距离和压缩时间等对注塑压缩成型的影响程度,得出了最优注塑压缩成型工艺参数组合方案,并对该工艺参数组合方案进行了模拟验证。最终得出最优工艺参数:模具温度为75℃,熔体温度为260℃,压缩力为60 t,压缩速度为14 mm/s,压缩距离为1.5 mm,压缩时间为7 s。     

Tailoring the crystalline structure of polypropylene parts molded through water‐assisted injection molding: Effects of melt temperature and polymeric nucleating agent

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     

Effects of silane on the properties of wood‐plastic composites with polyethylene‐polypropylene blends as matrices

The influence of 3‐(trimethoxysilyl)propyl methacrylate and benzoyl peroxide on gel content, crystallinity, and mechanical performance of unfilled PP‐PE blends, and their composites with wood was investigated. All materials were compounded in a twin screw extruder and then injection molded. Specimens were then exposed to high‐humidity and elevated temperature in a humidity chamber to cross‐link any unhydrolyzed silane. Adding wood to the PE‐PP blends, increased premature cross‐linking but also increased gel contents. However, the gel contents of the composites were still low. The PP component did not appear to cross‐link well and our gels were almost entirely HDPE. Fourier Transfer Infrared (FTIR) spectra provided additional evidence that TMSPM is grafted and cross‐linked in unfilled PE‐PP blends. Unfortunately, the spectra of wood composites proved difficult to interpret because of the complexity and overlap of the FTIR spectra of the wood. The HDPE component annealed when exposed to high‐humidity and elevated temperature, although less so in samples with high‐gel contents, presumably because of the decreased mobility. Annealing influenced mechanical performance, especially increasing moduli. Adding peroxide and silane appeared to improve adhesion between the wood flour and matrix in the composites but had little effect on energy absorbed during high‐speed puncture tests. Published 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical properties and morphological behavior of calcium carbonate‐filled polypropylene in dynamic injection molding

A custom‐made electromagnetic dynamic injection molding machine was adopted to study the mechanical properties and morphological behavior of calcium carbonate‐filled polypropylene (PP) in a dynamic injection molding process. The influence of vibration amplitude and frequency on the mechanical properties and morphological behavior of samples was investigated using tensile tests, notched Izod impact tests, differential scanning calorimetry, and scanning electronic microscopy. The tensile stress and the impact stress for all samples investigated were found to increase in a nonlinear manner with increasing vibration amplitude and frequency. The tensile stress reached a maximum value at about 8 Hz and 0.15 mm for neat PP and PP filled with 3, 20, and 30 wt% CaCO₃. For PP filled with 40 wt% CaCO₃, the tensile stress reached a maximum value at about 12 Hz and 0.2 mm. The impact stress reached a maximum value at about 12 Hz. From DSC experiments it was shown that the melting temperature slightly increased, but no new polymeric crystalline peak appeared under the vibration force field. The CaCO₃ particles were diffused easily and distributed evenly in the PP melt under the vibration force field, so it is very useful in improving the quality of injection products. Copyright © 2006 Society of Chemical Industry     

Thermal and mechanical properties of polypropylene/wood‐flour composites

In this research, polypropylene/wood‐flour composites (WPCs) were blended with different contents of wood and/or maleated polypropylene (MAPP) and clay. We found that the addition of MAPP or clay in the formulation greatly improved the dispersion of the wood fibers in the composite; this suggested that MAPP or clay may have played the role of an adhesion promoter in the WPCs. The results obtained with clay indicate that it also acted as a flame retardant. The thermal tests carried out with the produced samples showed an increased crystallization temperature (T_c), crystallinity, and melting temperature (T_m) with wood loading. The increase of the two former parameters was explained by the incorporation of wood flour, which played the role of nucleating agent and induced the crystallization of the matrix polymer. On the other hand, the T_m increase was ascribed to the insulating properties of wood, which hindered the movement of heat conduction. The effects of UV irradiation on T_m and T_c were also examined. T_c increased with UV exposure time; this implied that UV degradation generated short chains with low molecular weight that could move easily in the bulk of the sample and, thus, catalyze early crystallization. The flexural strength and modulus increased with increasing wood‐flour content. In contrast, the impact strength and tensile strength and strain decreased with increasing wood‐flour content. All of these changes were related to the level of dispersion of the wood flour in the polymeric matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Heterogeneity and anisotropy of injection‐molded discs of polypropylene and polypropylene composites

The anisotropy and heterogeneity of injection‐molded discs of polypropylene, talc‐filled polypropylene composites, and silane‐treated talc‐filled polypropylene composites are studied by means of dynamic mechanical analysis and thermomechanical analysis. The aims of this work are to discover the relationships between the structure of the composites, their anisotropic properties, and the heterogeneity of the molded discs. The experimental results show that although the discs are almost homogeneous, they present a high degree of anisotropy. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1275–1283, 2000     

Experimental investigation and numerical simulation of injection molding with micro‐features

Injection molding of thin plates of micro sized features was studied in order to manufacture micro‐fluidic devices for bioMEMS applications. Various types of mold inserts—CNC‐machined steel, epoxy photoresist, and photolithography and electroplating produced nickel molds—were fabricated and tested in injection molding. The feature size covers a range of 5 microns to several hundred microns. Issues such as surface roughness and sidewall draft angle of the mold insert were considered. Two optically clear thermoplastics, PMMA and optical quality polycarbonate, were processed at different mold and melt temperatures, injection speeds, shot sizes, and holding pressures. It was found that the injection speed and mold temperature in injection molding greatly affect the replication accuracy of microstructures on the metal mold inserts. The UV‐LIGA produced nickel mold with positive draft angles enabled successful demolding. Numerical simulation based on the 2D software C‐MOLD was performed on two types of cavity fillings: the radial flow and the undirectional flow. The simulation and experimental data were compared, showing correct qualitative predictions but discrepancies in the flow front profile and filled depth.     

Measurement and numerical prediction of fiber‐reinforced thermoplastics' thermal conductivity in injection molded parts

Recent improvements in injection molding numerical simulation software have led to the possibility of computing fiber orientation in fiber reinforced materials during and at the end of the injection molding process. However, mechanical, thermal, and electrical properties of fiber reinforced materials are still largely measured experimentally. While theoretical models that consider fiber orientation for the prediction of those properties exist, estimating them numerically has not yet been practical. In the present study, two different models are used to estimate the thermal conductivity of fiber reinforced thermoplastics (FRT) using fiber orientation obtained by injection molding numerical simulation software. Experimental data were obtained by measuring fiber orientation in injection molded samples' micrographs by image processing methods. The results were then compared with the numerically obtained prediction and good agreement between numerical and experimental fiber orientation was found. Thermal conductivity for the same samples was computed by applying two different FRT thermal conductivity models using numerically obtained fiber orientation. In the case of thermal conductivity, predicted results were consistent with experimental data measurements, showing the validity of the models. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39811.