Structural development of HDPE in injection molding

Abstract

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 Xray 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.

Calcium orthophosphate-based biocomposites and hybrid biomaterials

“…Other researchers used glutaraldehyde as a crosslinked reagent in various calcium orthophosphate-based biocomposites [388,392,500,502,503,520,525,585,621,646,649,917]. The interfacial bonding between calcium orthophosphates and other components might be induced by using various coupling agents and surface modifiers, such as silanes [192,234,337,540,[918][919][920][921][922][923], zirconates [225,337,339,914,924], titanates [225,337,924], phosphoric acid [543], alkaline pretreatment [722,725], polyacids [115,116,234], and other chemicals. Besides, some polymers might be grafted onto the surface of calcium orthophosphates [552].…”

Surface Structural Investigation of Starch‐Based Biomaterials

“…Several strategies can be followed to achieve the desired material ‘character’, including polymer synthesis/molecular design, polymer blending, chemical modification, among others. Starch‐based blends have shown4 a great versatility, being easily processed5–7 and proposed for applications such as drug delivery carrier systems,8 hydrogels and partially degradable bone cements,9 materials for bone replacement/fixation or fillers for bone defects10, 11 and porous structures to be used as scaffolds in tissue engineering of bone and cartilage 12, 13. Although the bulk properties of starch‐based biomaterials have been extensively characterised (mechanical properties, degradation behaviour),6, 11 there is no detailed study about their surface characteristics.…”

Integrated compounding and injection moulding of short fibre reinforced composites

“…Attempts to extend the mechanical performance of HDPE/HA composites, in order to meet the envisaged mechanical requirements, have been based on the use of hydrostatic extrusion 7,8 and shear controlled orientation in injection moulding (SCORIM). 9,10 In both cases, the main objective was to develop a high level of orientation in the HDPE matrix through control of the respective structure development during processing, in order to mimic the bone anisotropy. For the case of SCORIM, the enhancement in mechanical performance (as compared to conventional moulding routes) is associated with the shear induced crystallisation of the HDPE phase as a result of the specific moulding environment.…”

“…For the case of SCORIM, the enhancement in mechanical performance (as compared to conventional moulding routes) is associated with the shear induced crystallisation of the HDPE phase as a result of the specific moulding environment. 10,11 In spite of these promising results, the stiffness exhibited by these composites is still compromised by the low aspect ratio of the particulate HA and the low level of interfacial interaction between these and the polymer matrix. In order to overcome such limitations, additional enhancements in the mechanical performance of HDPE/HA composites have relied on the control of both the interfacial interaction and the filler dispersion by the use of coupling agents.…”

“…In order to overcome such limitations, additional enhancements in the mechanical performance of HDPE/HA composites have relied on the control of both the interfacial interaction and the filler dispersion by the use of coupling agents. 10 Further improvements in mechanical performance are expected through the use of more efficient reinforcement strategies. A complementary approach to the previous one is the selective reinforcement of the core of the composites, where the use of HA is redundant, with very stiff reinforcements such as carbon fibres (C fibres).…”