Effects of nano‐ and micro‐fillers and processing parameters on injection‐molded microcellular composites

The effects of submicron core‐shell rubber (CSR) particles, nanoclay fillers, and molding parameters on the mechanical properties and cell structure of injection‐molded microcellular polyamide‐6 (PA6) composites were studied. The experimental results of PA6 nanocomposites with 5.0 and 7.5 wt% nanoclay loadings and of CSR‐modified PA6 composites with 0.5 and 3.1 wt% CSR loadings were compared to their neat resin counterparts. This study found that nanoclay was more efficient in promoting a smaller cell size, larger cell density, and higher tensile strength for microcellular injection molding parts. A higher nanoclay loading led to more brittle behavior for microcellular parts. It was found that a proper amount of CSR particles could be added to the microcellular injection‐molded PA6 to reduce the cell size, increase the cell density, and enhance the toughness of the molded part. However, CSR particles were less effective cell nucleation agents as compared to nanoclay for producing desirable cell structures, and a higher CSR loading was found to have diminishing effects on the process and on the properties of the parts. POLYM. ENG. SCI., 45:773–788, 2005. © 2005 Society of Plastics Engineers     

TOF‐SIMS study of injection‐molded polystyrene

The purpose of this study was to provide experimental evidence of the separation of the polymer components at different scales during conventional processing. This was achieved by characterizing the surface and the bulk (cross section) of moldings manufactured with a high‐flow grade and a low‐flow grade of commercial polystyrene by the time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) analytical technique. Owing to the geometric constraints of the mold used, a weld was also obtained. Different surface spectra were observed for the two molded polystyrenes. The surface of the high‐flow grade moldings showed the spectral features of low‐molar polyolefin (paraffin) contaminants, whereas the bulk was dominated by polystyrene. Spectra from both the surface and the bulk of the low‐flow grade moldings were characteristic of polystyrene. Mold‐filling effects on the surface composition were observed in the flow front region of molded short‐shots of the low‐flow grade. The spectral changes indicated the abundance, in the surface, of the high end of the molar‐mass distribution of the material during the mold filling process. Two‐dimensional maps of the secondary ions from the low‐flow grade also showed an occasional alkali contamination, preferentially along the notch of the weld.     

Enhanced orientation of the water‐assisted injection‐molded ipp in the presence of nucleating agent

The nucleated isotactic polypropylene (iPP) was molded by water‐assisted injection molding. The crystalline morphology and orientation distribution were studied. The results show that shear brought by melt filling and pressurized water penetration can separately induce the formation of oriented structures in skin region (i.e., the region near mold cavity wall) and the water channel region. For virgin iPP, slightly oriented lamellae appear exclusively in the above aforementioned regions. However, shish‐kebab structure occurs not only in skin and water channel region of the iPP containing moderate content of nucleator (0.2 wt%) but also in the whole region of the iPP containing a higher content of nucleator (1 wt%). It is well known that nucleator cannot directly induce the development of shish‐kebab in the absence of shear, thus the results indicate: shear flow actually distributes over a much broader range than expected; in shear field, nucleator is significantly helpful for the shear which is not sufficient to solely induce oriented structure to promote the formation of the oriented structure. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

The cell forming process of microcellular injection‐molded parts

In this article, we studied the cell forming process of microcellular injection‐molded parts. Using a modified injection molding machine equipped with a Mucell^® SCF delivery system, microcellular‐foamed acrylonitrile–butadiene–styrene parts with different shot sizes were molded. The cell structure on the fractured surfaces along the direction both vertical and parallel to melt flow in the molded parts was examined. The results showed that a regular spherical cells region and a distorted ellipsoidal cells region exist in the molded parts simultaneously. The length of the distorted cells region along the melt flow direction in the molded parts remained basically unchanged for different shot sizes and it is about 195 mm away from the flow front in this study's conditions. The cell formation mechanism was analyzed, two cell forming processes in microcellular injection molding, the “foam during filling” process and the “foam after filling” process, were proposed. It was also found that the melt pressure in the filling stage is the dominant factor affecting the cell forming process, and there is a critical melt pressure value in the filling stage, 20.9 MPa, as the dividing line of the two cell forming processes in this study. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40365.     

Microhardness and water sorption in injection‐molded starch

The microhardness of injection‐molded potato starch was investigated in relation to the water sorption mechanism. The creep behavior under the indenter and the temperature dependence of the microhardness are reported. The influence of the drying time on microhardness, weight loss and density changes for materials with different injection‐molding temperatures is highlighted. Results reveal the role of the various mechanisms of water evaporation involved. The occurring structural mechanisms are discussed in terms of the gradual transformation of single helices of amylose and amylopectin into a network structure of double helices and the partial destruction of this structure. Experiments on starch samples, heated at 200°C, suggested the occurrence of an extreme densification of the network hindering the water adsorption in a humid atmosphere. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1246–1252, 2002     

Luminance of injection‐molded V‐groove light guide plates

Injection‐molded V‐groove light‐guide plates (LGPs) were made of two optical grade polycarbonates of different viscosities at various molding conditions. Their luminance as a function of viewing angle was measured. The depth of melt filling of the grooves in LGPs was measured at different locations selected based on the melt front propagation during the cavity filling. The depth of melt filling of grooves was mostly completed during the cavity‐filling stage. It was only slightly affected by the packing pressure and packing time and strongly affected by other molding conditions and layout of the V‐grooves. Luminance of LGPs showed a strong correlation with the depth of melt filling of the V‐grooves. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Viscoelastic flow analysis of surface morphology on injection‐molded polypropylene

The molecular orientation of a frozen layer in an injection‐molded specimen of a polypropylene–rubber blend was investigated. A typical V‐shaped pattern of birefringence was observed from the surface to the core in a crosscut section. From the comparison of the V‐patterns near the gate to the flow end, it was assumed that a frozen layer formed from the surface to a depth of 0.06 mm in a plaque (3 mm thickness) during the injection molding filling process. Numerical viscoelastic analysis of the fountain flow was carried out using an original 2D unsteady flow simulation program and ignored crystallization. A large extensional deformation formed just when the molten polymer contacted the cavity wall and the deformation immediately froze. A layer with a small birefringence between the surface and the shear‐oriented layer was divided into two parts. The depth profile of birefringence was compared to the principal stress difference calculated by numerical analysis. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Melting and crystallization behaviors of injection‐molded polypropylene

The melting and crystallization behaviors of the skin layer in an injection‐molded isotactic polypropylene (PP) have been studied, mainly in comparison with those of the core layer and subsidiarily in comparison with those of a compression‐molded PP and a nucleator (talc)–added PP. The skin layer contains about 5% crystals, which have a high melting point of up to 184°C. They thermally vanish by melting once. The subsequent melting history will scarcely affect the melting behaviors. On the other hand, crystallization behaviors are strongly affected by the melting history. The skin layer crystallizes in a wide temperature range at high temperature. This tendency weakens with increasing melting temperature, approaching a constant and that of the core layer above 230°C, which suggests that the memory effect of the residual structure of PP vanishes by melting above 230°C. In explaining these experimental results, it is assumed that the residual structure substance is a melt orientation of molecular chains that works as crystallization nuclei and that the vanishing of the residual structure is nothing but a relaxation of the melt orientation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1751–1762, 2000     

Effect of chitin addition on injection‐molded thermoplastic corn starch

A new type of biodegradable starch‐based composites was prepared by injection‐molding using glycerol and water as plasticizers. Chitin flakes, obtained from shells of Penaeusschmitti, were used as reinforcing phase. The effect of chitin content on the structural and tensile properties of the composite samples was examined after conditioning at 28°C and 80% relative humidity for 30 days. In general, chitin incorporation into the starch matrix resulted in materials with higher modulus and decreased elongation at break. Wide‐angle X‐ray diffraction and differential scanning calorimetry evidenced a significant decrease in crystallinity in the composite samples in relation to the unfilled starch material. Contact angle measurements revealed that the addition of chitin contributes to the improvement of water resistance of the composite samples when compared to injection molded starch alone. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2706–2713, 2004     

Evaluation of processing effects in injection‐molded amorphous and crystalline thermoplastics using an excimer laser

The ablation behavior of amorphous [polystyrene (PS), polycarbonate (PC)] and crystalline [PET, glass‐filled poly(butylene terephthalate) (PBT)] polymers by 248‐nm KrF excimer laser irradiation were investigated for different injection‐molding conditions, namely, injection flow rate, injection pressure, and mold temperature, as a possible method for evaluating processing effects in the specimens. For this purpose, dumbbell‐shaped samples were injection‐molded under different sets of processing conditions, and weight loss measurements were carried out for the different injection‐molding conditions. Some of the crystalline (PET) samples were annealed at different annealing times and temperatures. For PET, the weight loss decreased with increasing mold temperature and remained insensitive to injection flow rate. Annealing time and temperature significantly reduced weight loss in PET. For PBT, the weight loss due to laser ablation decreased with increasing material packing due to pressure, and it also showed some sensitivity to flow rate variation. The major effect was seen with glass‐filled PBT samples. The weight loss decreased drastically with increasing glass fiber content. Laser ablation allowed us to observe process‐induced fiber orientation by scanning electron microscopy in PBT samples. For PS and PC, the weight loss increased with increasing injection flow rate and mold temperature and decreased with increasing injection pressure. The position near the gate showed higher ablation than the position at the end for all the conditions. A decrease in the material orientation with injection speed and mold temperature led to an increase in the weight loss, whereas an increase in the injection pressure, and consequently orientation, led to a lower weight loss for PS and PC. Higher residual stress samples showed higher weight losses. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 2006     

Ghost marks—gloss‐related defects in injection‐molded plastics

The production of injection‐molded parts free from surface appearance defects is of great importance in the manufacturing of high‐quality products. A particular surface defect which occurs on components manufactured from an acrylonitrile‐butadiene‐styrene copolymer (ABS) is here described. The defect has been called ghost marks and is characterized by a local change in gloss or lightness which is only visually detectable in certain viewing angles and conditions of illumination. By means of scanning electron microscopy, small‐scale deformations of the surface texture were observed in the area of the defect which in turn alters the light scattering properties of the surface. The light scattering properties were evaluated by means of a multiangle spectrophotometer. The holding pressure during the injection molding process was shown to play a significant role in the formation of the ghost marks possibly imposing forces causing the deformation of the surface texture. The deformations may also occur from nonuniform thermal surface shrinkage during cooling. The type of texture and wall thickness also influences the occurrence of ghost marks.POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Angle‐resolved light scattering from textured injection‐molded plastics

With regard to surface appearance, the angle‐resolved light scattering from textured polymeric surfaces was evaluated to link the reflectance properties to measured gloss as well as visually perceived gloss. Bidirectional reflectance distributions were determined by means of a scatterometer and the specimens involved were textured injection‐molded plaques manufactured from three different polymers; an acrylonitrile‐butadiene‐styrene (ABS) copolymer, a polypropylene (PP), and a polycarbonate and ABS copolymer blend (PC/ABS). The influence of color, surface roughness, and angle of incidence on the scattering characteristics was evaluated. An off‐specular reflectance peak was observed for the textured specimens the magnitude of which was clearly determined by the surface roughness and the angle of incidence. The color of the specimens mainly influenced the diffuse reflectance. The results provide a measure of perceived gloss and supported previously reported findings regarding the relevance of the concept of contrast gloss for the gloss characterization of textured polymeric surfaces. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The relationship between mechanical properties and morphology of vibration‐injection‐molded polyethylene

This paper introduces a novel melt vibration‐injection molding. The effect of mid‐frequency melt vibration on mechanical properties was introduced, and SEM, WAXD and DSC investigations had been employed to provide evidence for explaining the relationship between mechanical properties and morphology of vibration‐injection‐molded specimens. The results show that the effect of vibration frequency is very different from that of vibration pressure amplitude. At a given vibration pressure amplitude, the increase of vibration frequency is beneficial for obtaining preferential orientation, more perfect lamellae and enhanced mechanical properties. For a given vibration frequency, increase of vibration pressure amplitude is a pre‐requisite for the achievement of a large‐scale lamella, more pronounced orientation, increase of cyrstallinity and high strength of high‐density polyethylene, but part of the toughness is lost. Copyright © 2004 Society of Chemical Industry     

Durability of polylactide‐based polymer blends for injection‐molded applications

The durability of polylactide (PLA) blended with polycarbonate (PC) was assessed by exposure to conditions of elevated temperature and humidity over a period of several weeks. Mechanical performance, moisture absorption, chemical composition, and thermal properties were monitored as a function of continuous conditioning at 70°C and 90% relative humidity (RH). All PLA and PC/PLA blends showed significant moisture absorption and hydrolysis, resulting in degradation of properties. Furthermore, while the addition of PC was intended to improve the durability of the blend over neat PLA, it was found that the hydrolysis products of PLA accelerated the degradation of PC itself. This study shows for the first time the hydrolysis behavior of PC/PLA blends in an increasingly acid environment during heat and humidity conditioning. These injection‐molding grades of PLA‐based resins are currently not suitable for use in applications that require long‐term durability in environments subject to elevated temperature and humidity, such as automotive interiors. Further material formulation work is required before use in injection‐molded applications for automotive. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Simulations on structure performance of 3C thin‐wall injection‐molded parts

Manufacturing of 3C (Computer, Communication, and Consumer Electronics) products toward weight reduction, thin‐wall, and minified‐size is an inescapable trend for the future 3C industries. However, the induced damage information from drop impact, including exterior housing fracture, liquid crystal display (LCD) cracking, solder‐joint breaking, or interior component failure, is still derived experimentally and involves very complicated parametric analyses, such as a dynamic impact process, drop orientation, contact behavior, and large deformation during the impact instance. In the present study, numerical simulations for the drop test and bending strength were applied to a thin‐wall computer dictionary (Model CD‐66) housing to understand the key factors that affect the part drop test performance. The appropriate modeling that would affect simulation accuracy as well as the associated nodal degree of freedom and computer time were also investigated. A housing of CD‐66 was redesigned to be 1 mm thick and structurally verified with two different plastics: polycarbonate (PC) and acrylonitrile butadiene styrene (ABS). The simplification of the PC board and LCD backlight circuit in finite element modeling (FEM) only causes about a 10% difference, while saving many modeling costs. The numerical simulations also indicate that both its bending strength and drop‐impact strength were decreased only about 5%, whereas the product quality still met its strength requirement if only the top housing plate thickness was reduced while the remaining sidewall thickness was kept unchanged. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3064–3071, 2002     

Influence of compatibilizers and processing temperature on microcellular injection‐molded polypropylene/(waste tire powder) composites

Nowadays the economic recycling of waste tires has become a global challenge. The use of waste tire powder as a dispersed elastomeric phase in a polypropylene (PP) matrix offers an interesting opportunity for recycling of waste tire rubber. Compatibilized PP/(waste tire powder) composites are microcellularly processed to create a new class of materials with unique properties. Recent studies have demonstrated the feasibility of developing microcellular structures in PP/waste ground rubber tire (WGRT) composites. Microcellular PP/WGRT composites are prepared by an injection‐molding process using a chemical blowing agent. In this study, cell sizes, cell density, void fraction, and mechanical properties of the composite foams were measured, as well as the shear viscosity of the unfoamed composites. The influence of various compatibilizers and processing temperatures on cell morphology and the mechanical properties of injection‐molded PP/WGRT composites were investigated. It was seen that the addition of maleic anhydride‐grafted styrene‐ethylene‐butylene‐styrene (SEBS‐g‐MA) increased the shear viscosity of the composites. The void fraction and cell density of the PP/WGRT composites increased with addition of compatibilizers, whereas the average cell sizes decreased. A processing temperature range of 180–195°C gave finer microcellular structure and regular cell distribution. The SEBS‐g‐MA enhanced the elongation properties and acted as an effective compatibilizer in this particular system. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

The mechanical/thermal properties of microcellular injection‐molded poly‐lactic‐acid nanocomposites

This study investigated the influence of montmorillonite (MMT) content on the mechanical/thermal properties of microcellular injection‐molded polylactide (PLA)/clay nanocomposites. Carbon dioxide was the blowing agent. The PLA/MMT nanocomposites were prepared by twin screw extrusion. The results showed that as MMT content is increased, tensile strength, impact strength, and cell density decrease. This is caused by the speed degradation of PLA due to the addition of MMT. MMT decreases the crystallization temperature but increases the decomposition temperature of the nanocomposites. The XRD results showed that the layer spacing of the clay increases as MMT content increases. TEM pictures showed that the MMT is well dispersed within the PLA matrix. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.     

Warpage and countermeasure for injection‐molded in‐mold labeling parts

Decades ago, the production of packaging with the injection in‐mold labeling (IML) has been established. With this manufacturing technique, label and packaging, both are of the same polymeric material, become inseparably connected during the injection molding process. Because thermal conductivity of the polymeric label material is clearly smaller than that of the metal mold wall, thermal‐induced warpage of injected IML parts or part surface deformation could occur. In this study, structure and warpage behavior of IML parts, which are different from those of conventional molded parts without labels were intensively investigated. It was found that it is the volume contraction difference between label and substrate that forces IML parts to warp to the opposite side of the label. In addition, IML part warpage problem can be coped by varying the mold temperature on the stationary and moving mold platen. By increasing the mold temperature on the label side, the degree of IML part warpage can be reduced with acceptable reduction in mechanical properties. The optimum mold temperature range for particular substrate material, however, was found to be more decisive in maintaining the modulus of elasticity of IML parts than the magnitude of mold temperature difference. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Micromechanical properties of injection‐molded starch–wood particle composites

The micromechanical properties of injection‐molded starch–wood particle composites were investigated as a function of particle content and humidity conditions. The composite materials were characterized by scanning electron microscopy and X‐ray diffraction methods. The microhardness of the composites was shown to increase notably with the concentration of the wood particles. In addition, creep behavior under the indenter and temperature dependence were evaluated in terms of the independent contribution of the starch matrix and the wood microparticles to the hardness value. The influence of drying time on the density and weight uptake of the injection‐molded composites was highlighted. The results revealed the role of the mechanism of water evaporation, showing that the dependence of water uptake and temperature was greater for the starch–wood composites than for the pure starch sample. Experiments performed during the drying process at 70°C indicated that the wood in the starch composites did not prevent water loss from the samples. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4893–4899, 2006