Structure and physical property relationships in processed polybutene‐1

The effect of SCORIM was investigated on three grades of polybutene‐1 and one grade of ethylene–butene‐1 copolymer. The methods and processing conditions used for injection molding and the properties of the moldings are reported. Phase transformations and their relationship with mechanical properties are discussed in detail. Both, conventional and shear‐controlled orientation injection molding (SCORIM) were employed to produce moldings. SCORIM is based on the application of specific macroscopic shears to a solidifying melt. The multiple shear action enhances molecular alignment. The moldings were investigated by performing mechanical tests, fractographic analysis, differential scanning calorimetry studies, wide‐angle X‐ray diffraction, polarized light microscopy, and atomic force microscopy. The application of SCORIM improves the mechanical performance. Molecular orientation results in the formation of shish‐kebab morphology. One grade of polybutene‐1 exhibited a greater than fivefold increase in Young's modulus. The application of high cavity pressures favored the formation of the stable Form I' in polybutene‐1. The formation of Form I' led to a decrease in crystallinity and mechanical properties. However, this loss was by far smaller than the gain obtained via the formation of shish‐kebab morphology. The relationship between mechanical properties and micromorphologies of the investigated materials is explained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 814–824, 2003     

Structure development and interfacial interactions in high‐density polyethylene/hydroxyapatite (HDPE/HA) composites molded with preferred orientation

Composites of high‐density polyethylene (HDPE) filled with sintered and nonsintered hydroxyapatite (HA) powders, designated as HAs and HAns, respectively, were compounded by twin screw extrusion. Compounds with neoalkoxy titanate or zirconate coupling agents were also produced to improve interfacial interaction and filler dispersion in the composites. The composites were molded into tensile test bars using (i) conventional injection molding and (ii) shear‐controlled orientation in injection molding (SCORIM). This latter molding technique was used to deliberately induce a strong anisotropic character to the composites. The mechanical characterization included tensile testing and microhardness measurements. The morphology of the moldings was studied by both polarized light microscopy and scanning electron microscopy, and the structure developed was assessed by wide‐angle X‐ray diffraction. The reinforcing effect of HA particles was found to depend on the molding technique employed. The higher mechanical performance of SCORIM processed composites results from the much higher orientation of the matrix and, to a lesser extent, from the superior degree of filler dispersion compared with conventional moldings. The strong anisotropy of the SCORIM moldings is associated with a clear laminated morphology developed during shear application stage. The titanate and the zirconate coupling agents caused significant variations in the tensile test behavior, but their influence was strongly dependent on the molding technique employed. The application of shear associated with the use of coupling agents promotes the disruption of the HA agglomerates and improves mechanical performance. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2873–2886, 2002     

The enhancement of the mechanical properties of a high-density polyethylene

This paper describes the process optimization in injection molding of high-density polyethylene (HDPE). Both conventional injection molding and shear controlled orientation (SCORIM) were employed in processing. The process optimization was based on design of experiments and complemented with analysis of variance. Mechanical characterization was carried out by tensile testing. Wide-angle X-ray diffraction and differential scanning calorimetry were used for the structural characterization of the moldings. High-density polyethylene exhibits 7.2 GPa Young's modulus and 155 MPa of ultimate tensile strength following the application of SCORIM processing. These results account for a fourfold increase in Young's modulus and a fivefold increase in ultimate tensile strength compared to conventional injection molding. The maintenance of toughness while enhancing stiffness and strength of the SCORIM moldings is attributable to an oriented morphology developed during shear flow, i.e., shish-kebab structure. The frequency of shearing action has the strongest influence on the morphology development. It is also demonstrated that the studied parameters are very much interdependent. It is possible to achieve substantial gains in mechanical properties of HDPE in SCORIM processing without causing a substantial increase in cycle time. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2473–2483, 1999     

Injection molding of a starch/EVOH blend aimed as an alternative biomaterial for temporary applications

Biodegradable polymers show great potential to be used as materials for temporary implants and bone replacement applications in orthopedics. However, its use in high load‐bearing applications will depend on the successful development of biodegradable implants with a mechanical performance matching that of human bone. This article describes the optimization of the injection molding process of an alternative biodegradable starch‐based polymer aimed at biomedical applications. A blend of starch with a copolymer of ethylene–vinyl alcohol (SEVA‐C) was studied. Both conventional injection molding and shear controlled orientation (SCORIM) were optimized with the support of design of experiments and analysis of variance techniques. The mechanical characterization was performed by tensile testing. The structure developed within the moldings was assessed by wide‐angle X‐ray diffraction and differential scanning calorimetry. Increases up to 30% in the tangent modulus and 20% in the ultimate tensile strength compared with conventional molding were achieved with the application of SCORIM. The holding pressure and the frequency of the shear applied have the strongest influence on the morphology development and consequently on the mechanical performance. The solidification of SEVA‐C at high cavity pressures enhances stiffness for long durations of the shearing stage in SCORIM. However, the effect of viscous heating of SEVA‐C is important and ought to be considered. A decrease of the material phase miscibility in SEVA‐C occurs as result of the shear fields imposed. The microstructure evaluation suggests that the mechanical properties enhancement in SCORIM molded SEVA‐C is attributable to preferred orientation developed during processing. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1303–1315, 2000     

Mechanical performance of starch based bioactive composite biomaterials molded with preferred orientation

Composites of blends of starch with ethylene vinyl alcohol copolymer (SEVA‐C) filled with 10, 30 and 50% by weight (wt.) of hydroxyapatite (HA–the major inorganic constituent of human bone) were produced by twin‐screw extrusion (TSE) compounding. These composites were molded into tensile test bars using two molding techniques: (i) conventional injection molding and (ii) shear controlled orientation in injection molding (SCORIM). The bars produced were mechanically characterized by means of tensile testing and dynamical mechanical analysis (DMA). The structure of the moldings was assessed by wide‐angle X‐ray diffraction (WAXD) and the failure surfaces of the moldings analyzed by scanning electron microscopy (SEM). The enhancement of stiffness observed with HA reinforcement results partially from the stiffening effect of the blend associated with the decrease in plasticizer content during the compounding stage. SCORIM was able to further increase the stiffness of SEVA‐C/HA composites, allowing a maximum improvement of 12% for 30% wt. HA as compared to conventional molding. DMA results showed that the reinforcement of SEVA‐C causes the broadening of the relaxation peak of the polymer, suggesting a structural change within the starch fraction that may be related with thermal degradation of the polymer. The addition of HA particles reduces the preferred orientation exhibited by the SEVA‐C matrix, which is believed to limit the maximum mechanical performance that can be attained. Nevertheless, composites based on a biodegradable matrix with modulus above 7 GPa (in the bounds of the lower limit for human cortical bone) could be successfully produced.     

Structural development of HDPE in injection molding

This study investigated some relevant structure/properties relationships in shear‐controlled orientation in injection molding (SCORIM) of high‐density polyethylene (HDPE). SCORIM was used to deliberately induce a strong anisotropic character in the HDPE microstructure. Three grades with different molecular weight characteristics were molded into tensile test bars, which were subsequently characterized in terms of the mechanical behavior by tensile tests and microhardness measurements. The structure developed upon processing was also characterized by polarized light microscopy (PLM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WAXD). SCORIM allows the production of very stiff molded parts, exhibiting a very well‐defined laminated morphology. This morphology is associated with both an M‐shaped microhardness profile and a pronounced mechanical anisotropy. These characteristics are supported by an analogous variation in the crystallinity and a high level of molecular orientation, as indicated, respectively, by calorimetric measurements and X‐ray diffraction results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2079–2087, 2003     

Shear controlled orientation in injection moulding of starch based blends intended for medical applications

Abstract

Biodegradable polymeric implants are considered to be good alternatives to metallic implants in several temporary applications. Aliphatic polyesters have been extensively investigated and have been employed in several biomedical applications. More recently, biodegradable starch based polymeric blends have also been considered as alternative materials. In this study, the effect of shear controlled orientation injection moulding (SCORIM) on the mechanical properties and degradation behaviour of starch-polylactide and starch-poly(ethylene-co-vinyl alcohol) blends has been investigated and compared with those produced by conventional injection moulding. The changes in these properties has also been studied when using an hydroxyapatite filler to reinforce the polymeric matrixes. The SCORIM processing enhanced the unidirectional mechanical properties substantially. The incorporation of hydroxyapatite into the polymer matrix had a stiffening effect but also reduced the strength and toughness. Generally, the mechanical properties deteriorated substantially in vitro. Reinforcement by hydroxyapatite was found to be less effective than expected in a wet environment.     

Crystalline morphology of isotactic polypropylene (iPP) in injection molded poly(ethylene terephthalate) (PET)/iPP microfibrillar blends

The poly(ethylene terephthalate) (PET)/isotactic polypropylene (iPP) in situ microfibrillar blends have been prepared through a “slit die extrusion-hot stretch-quenching” process, in which PET assumes microfibrils with 0.5-15 μm in diameter depending on the hot stretching ratios (HSR, the area of the transverse section of the die to the area of the transverse section of the extrudate). The injection molded specimens of virgin iPP and the PET/iPP blends were prepared by conventional injection molding (CIM) and by shear controlled orientation injection molding (SCORIM), respectively. The effect of shear stress and PET phase with different shape on superstructures and their distribution of injection molded microfibrillar samples were investigated by means of small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS). The shear (or elongational) flow during CIM and SCORIM can induce oriented lamellae (i.e. kebabs induced by shish). The shish-kebab structure appears not only in the skin and intermediated layers of CIM samples, but also in the whole region of SCORIM samples. For the neat iPP samples, a more “stretched” shish-kebab structure with higher orientation degree can be obtained in the interior region (intermediate and core layers) by the SCORIM method; moreover, the SCORIM can result in the growth of β-form crystal both in intermediate layer and in core layer, which only appears in intermediate layer of the neat iPP samples obtained by CIM. For the PET/iPP blends, interestingly, the addition of microfibrils as well as their aspect ratios can affect the orientation degree of kebabs only in the intermediate layers, and the addition of microfibrils with a low aspect ratio can bring out a considerable increase in the orientation degree of kebabs along the flow direction. However, for the SCORIM, the addition of microfibrils seems to be a minor effect on the orientation degree of kebabs, and it tends to hamper the formation of a more “stretched” shish-kebab structure and suppresses the growth of β-form crystal distinctly. Furthermore, It appears from experiment that γ-form crystals can grow successfully in this oriented iPP melt with the synergistic effect of shear and pressure only when the growth of β crystals can be restrained by some factors, such as the PET dispersed phase and thermal conditions (cooling rate).     

Self‐interference flow of an isotactic polypropylene melt in a cavity during injection molding. II. Morphology and crystallinity

This article is principally concerned with the morphology and crystallinity of isotactic polypropylene (iPP) parts molded by injection molding, during which a self‐interference flow (SIF) occurs for the melt in the cavity. Scanning electron microscopy shows that a transverse flow takes place in SIF samples. Wide‐angle X‐ray diffraction and differential scanning calorimetry show that SIF moldings exhibit a γ phase, in addition to α and β phases, and high crystallinity. Meanwhile, the results for iPP moldings made by the conventional flow process, that is, conventional injection molding, are reported for comparison. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2791–2796, 2003     

Controlled orientation of reflective pigment and optical property characterization of injection-molded polypropylene

The aims of the research reported were to explore the possibility of removing surface weld lines from highly reflective aluminum pigmented polypropylene injection moldings. Moldings were optically characterized and their characteristics attributed to pigment orientation present in the samples. Conventional injection molding and two novel molding techniques were employed for this investigation, Shear Controlled Orientation Injection Molding (SCORIM) and Bright Surface Molding (BSM). Further, the two techniques, SCORIM and BSM, were used in series and termed SBM to remove surface weld lines. The use of SBM enabled the re-orientation of the pigment in order to induce a uniform direction for the “flip-flop” effect where flow fronts have impinged from different directions. These moldings were then quantitatively characterized using a gonio-spectrophotometer. Their different reflective surface characters were then related to the angle of orientation induced by the respective processing technologies used.     

Mechanical properties of glass fiber reinforced polypropylene injection molded with a rotation mold

A special mold (Rotation, Compression, and Expansion Mold) was used to impose a controlled shear action during injection molding of short glass fiber reinforced polypropylene discs. This was achieved by superimposing an external rotation to the pressure‐driven advancing flow front during the mold filling stage. Central gated discs were molded with different cavity rotation velocities, inducing distinct levels of fiber orientation through the thickness. The mechanical behavior of the moldings was assessed, in tensile and flexural modes on specimens cut at different locations along the flow path. Complete discs were also tested in four‐point flexural and in impact tests. The respective results are analyzed and discussed in terms of relationships between the developed fiber orientation level and the mechanical properties. The experimental results confirm that mechanical properties of the moldings depend strongly on fiber orientation and can thus be tailored by the imposed rotation during molding. POLYM. ENG. SCI. 46:1598–1607, 2006. © 2006 Society of Plastics Engineers.     

A comparison of short glass fiber reinforced polypropylene plates made by conventional injection molding and using shear controlled injection molding

This paper describes a comparison of the fiber orientation structures and resulting elastic properties of samples of short glass fiber filled polypropylene made by conventional injection molding and by the SCORIM (Shear Controlled Orientation in Injection Molding) process developed at The University of Brunel. The 3D fiber orientation distributions of the composites were measured using a unique transputer based image analysis system developed at The University of Leeds. The mechanical properties of the samples were characterized using an ultrasonic velocity technique, which allows a full set of elastic constants to be determined for each material. The link between fiber orientation distributions and measured elastic properties was then investigated using theoretical models developed in this laboratory.     

The effect of orientation on the mechanical properties of injection molded polystyrene

The deformation and fracture behavior of injection molded plaques have been determined, and the results interpreted in terms of the effect of molecular orientation on the crazing and shear yielding behavior. The molecular orientation was characterized by optical birefringence. A range of injection molding conditions and two mold thicknesses were Used and this resulted in a large variation in the molecular orientation, particularly through the sheet thickness. Tensile tests were made on samples cut at different angles to the injection molding direction. The moldings are considered to consist of a composite of layers of material with different orientation, and the properties of the samples cut from the molding are analyzed in terms of the properties of each layer. Results from material oriented unidirectionally by hot drawing have been used to predict the composite properties, and good agreement has been obtained.     

Preparation and studying properties of polybutene‐1/thermoplastic starch blends

Starch as an inexpensive and renewable source has been used as a filler for environmental friendly plastics for about two decades. In this study, glycerol was used as a plasticizer for starch to enhance the dispersion and the interfacial affinity in thermoplastic starch (TPS)/polybutene‐1(PB‐1) blend. PB‐1 was melt blended with TPS using a single screw extrusion process and molded using injection molding process to investigate the rheological and mechanical properties of these blends. Rheological properties were studied using a capillary rheometer, and the Bagley's correction was performed. Mechanical analysis (stress–strain curves) was performed using Testometric M350‐10 kN. The rheological properties showed that the melt viscosity of the blend is less than that of PB‐1, and the flow activation energy at a constant shear stress of the blend increases with increasing glycerol content in the blend. The mechanical experiments showed that both stress and strain at break of the blends are less than that of PB‐1, whereas the Young's modulus of the most blends is higher than that of PB‐1 which confirms the filling role of TPS in the blend. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Morphology−performance relationship of polypropylene−nanoclay composites processed by shear controlled injection moulding

A nanoclay based masterbatch was mixed with polypropylene (PP) and injection moulded by conventional (CIM) and shear controlled orientation (SCORIM) injection moulding techniques. The aim was to correlate the morphologies induced by SCORIM and CIM processing with the thermal, mechanical and fracture performance of thick PP/nanoclay mouldings. In SCORIM, two extreme shear levels were applied by changing processing conditions. A complete characterization is reported, and statistical analysis was carried out to obtain a relationship between moulding properties. Nanoclay acted as a polymer morphology director, and in combination with SCORIM it induced the formation of the γ polymorph of PP. The nanoclay has a strong positive effect on the thermal degradation of PP under an oxidative atmosphere, due to the barrier effect of clay and the physico‐chemical adsorption of volatile degradation products on the silicates, but there were no differences between processing techniques. SCORIM samples of neat PP showed nonlinear brittle behaviour, while nanocomposites exhibited quasi‐stable behaviour induced by a large deformation capability of the skin. Although fracture initiates at practically the same loading levels, the overall propagation energy values varied with processing conditions. Statistical analysis indicates that the decrement of the core region achieved by SCORIM processing, the differences between skin and core and the PP γ phase induced by the presence of nanoclay are responsible for the toughening of SCORIM PP/nanoclay mouldings. © 2013 Society of Chemical Industry     

Structure and properties of injection moldings of polypropylene/polystyrene blends

A homoisotactic polypropylene (PP) was melt blended with 0–30 wt % of three kinds of polystyrene (PS) with melt flow indexes lower than, similar to, and higher than that of PP. The blends were injection molded at cylinder temperatures of 200–280°C, and the structure and properties of the injection moldings were studied. With PS blending, although the PP molding whitened, no surface defect such as layer peeling and pearl-like appearance occurred. The rigidity and dimensional accuracy of the molding improved without much deterioration in impact strength and heat resistance. At the same time the fluidity also improved. The injection moldings of PP/PS blends did not show clear skin/core structure under a polarizing microscope. The degrees of crystallinity and crystalline c-axis orientation decreased with PS blending. PS particles were the smallest when the ratio of the viscosity of the PS to that of PP at molding shear rate was slightly lower than unity. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1015–1027, 1997     

Bi‐axial self‐reinforcement of high‐density polyethylene induced by high‐molecular weight polyethylene through dynamic packing injection molding

Previously, bi‐axial self‐reinforcement of high‐density polyethylene (HDPE) was achieved through a uni‐axial shear stress field introduced by dynamic packing injection molding technology. Here, further improvement of tensile strength along the flow direction (MD) was achieved by blending a small amount of high‐molecular‐weight polyethylene (HMWPE) with HDPE, while the tensile strength along the transverse direction (TD) still substantially exceeded that of conventional moldings. Tensile strengths in both flow and transverse directions were considerably enhanced, with improvements from 23 MPa to 76 MPa in MD and from 23 MPa to 31 MPa in TD. The effect of HMWPE content and molding parameters on tensile properties was also investigated. The tensile strength along MD was highly dependent on HMWPE content, oscillating cycle, mold temperature, melt temperature and packing pressure, while that along TD was insensitive to composition and processing parameters within the selected design space. According to the stress–strain curves, samples with HMWPE produced by dynamic packing injection molding had a special tensile failure mode in MD, different from both typical plastic and brittle failure modes. There were no yielding and necking phenomena, which are characteristic during tensile testing of plastic materials, but there was still a considerably higher elongation compared to those of brittle materials. However, in TD, all dynamic injection molding samples exhibited plastic failure as did typical conventional injection molding samples. Copyright © 2006 Society of Chemical Industry     

Formation mechanism of high-pressure water penetration induced fiber orientation in overflow water-assisted injection molded short glass fiber-reinforced polypropylene

Recently, there has been growing interest in water-assisted injection molding (WAIM) not only for its advantages over gas-assisted molding (GAIM) and conventional injection molding (CIM), but also for its great potential advantages in industrial applications. To understand the formation mechanism of water penetration induced fiber orientation in overflow water-assisted injection molding (OWAIM) parts of short glass fiber-reinforced polypropylene (SGF/PP), in this work, the external fields and water penetration process within the mold cavity were investigated by experiments and numerical simulations. The results showed that the difference of fiber orientation distribution in thickness direction between WAIM moldings and CIM moldings was mainly ascribed to the great external fields generated by water penetration. Besides, fiber orientation depended on the position both across the part thickness and along the flow direction. Especially in the radial direction, fiber orientation varied considerably. The results also showed that the melt temperature is the principal parameter affecting the fiber orientation along the flow direction, and a higher melt temperature significantly facilitated more fibers to be oriented along the flow direction, which is quite different from the results as previously reported in short-shot water-assisted injection molding (SSWAIM). A higher water pressure, shorter water injection delay time, and higher melt temperature significantly induced more fibers to be orderly oriented in OWAIM moldings, which may improve their mechanical performances and broaden their application scope.     

In situ fibrous structure oriented polymer blends composed of poly(lactic acid) and polycaprolactone containing peroxide

A fibrous dispersed phase stuffed with polycaprolactone (PCL) was constructed in a poly(lactic acid) (PLA) matrix during an injection‐molding process. The injection‐molding process showed efficiency in forming dispersions with fibrous shapes, and they could impart the ductile property of PCL to the brittle PLA matrix, with appropriate interfacial adhesion arising from the cocrosslinking structure at the PLA/PCL interface by dicumyl peroxide (DCP). However, the addition of excess DCP caused a split of the dispersions resulting from the compatibility increment and the excess crosslinking reaction at the interface and inside each phase. The addition of a small amount of DCP could adhere the interface without splitting of the dispersions. The observed internal structure in the injection moldings showed a morphology transition that changed gradually from a fine fibrous morphology to a coarse morphology at a deeper position in the injection moldings. The tensile properties of sliced local layers, which were fabricated with a sliding microtome, proved that the fibrous morphology was effective in the improvement of ductility of the blends. An X‐ray analysis showed that the shear flow increased the crystalline orientation and formed a different crystalline structure only in the PCL dispersed phase, but its crystalline structure was not the main factor for ductility improvement. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Ultrasonic measurement of orientation in HDPE/iPP blends obtained by dynamic packing injection molding

The orientation of polymer chain has a great effect on its mechanical properties, therefore, it is always an important issue on how to characterize, accurately and quickly, the orientation of polymer chain during processing. In this article, according to the property that ultrasound travels in different velocities in anisotropic media, normal incident shear wave was utilized to explore the orientation structure of HDPE/iPP blends obtained by dynamic packing injection molding. The ultrasonic technique is consistent with the 2D-WAXS in charactering the orientation degree of polymer chains, although ultrasonic technique focuses on the overall orientation of polymer blends while the 2D-WAXS reveals the crystalline orientation of each component. Our work demonstrates that ultrasonic technique might be a reliable, fast and easy way to characterize the orientation structure of crystalline polymer blends. The ultrasonic measurements were performed off-line, but the achievement provides the possibility for on-line detection of orientation structure in injection molding by using ultrasonic technique.