Process-property-structure relationship in miniaturized injection moulded polyoxymethylene samples

Abstract

Micro‐injection moulding is one of the key manufacturing technologies for thermoplastic polymeric materials for the mass production of high value miniaturized components. However, this process is not just a straightforward down scaling of the conventional injection moulding technique. Indeed, during the micro‐injection the polymer melt is forced to flow at high strain rates through very small channels in nonisothermal conditions; this can lead to complex microstructures and to parts with unexpected performances. In this work, the relationships among the processing conditions, the mechanical properties and the microstructural characteristics of polyoxymethylene miniaturized specimens obtained by injection moulding were investigated. The attention was focused on the influence of the process temperatures on the mechanical behavior, examined by uniaxial tensile tests, and on the microstructural characteristics of the specimens, examined by differential scanning calorimetry, wide‐angle X‐ray diffraction, polarized light microscopy, and dynamic‐mechanical thermal analysis. The results highlighted that material ductility in the miniaturized specimens is significantly affected by the mould temperature, because of the sample microstructure. Different degrees of orientation of polymer crystallites and different morphologies of the skin/core transition region were observed in dependence on the process temperatures. POLYM. ENG. SCI., 54:512–521, 2014. © 2013 Society of Plastics Engineers

Mechanical characterisation and replication quality analysis of micro-injected parts made of carbon nanotube/polyoxymethylene nanocomposites

“…The absence of significant degradation phenomena of POM chains during the micro-injection process of the unfilled polymer, has been verified in a previous work, 40 with process conditions very similar to those used in the present work.…”

Mechanical properties of micro-injected HDPE composites

“…The PLM images (Figure 2a and b), on the pristine polymer, show clearly the "skin layer" and the other intermediate regions according with the definition provided by Giboz et al [21,22]. The extension of the skin layer (outer region) seem to be larger in the HDPE″ processed with MIN condition according with the literature [8] but a precise quantification is not possible due to the gradual modification of the structure from the core to the skin. Both the samples show a "core", structurally similar, but with dimensions remarkably different.…”

“…The moulded component here examined is a micro scale dog-bone tensile sample with thickness of 1 mm, length of 12 mm and width of 1.5 mm in the narrow part and 3 mm in the larger one. A detailed description of the miniaturized specimen is provided in [8]. The injection moulding tests have been carried out into two steps: a screening phase in order to identify the working technological window for pristine polyethylene (Table 2), then a set of experiments with HDPE'-GB and HDPE"-TA composites using the two extreme levels of the process conditions ("MIN" and "MAX" of operative window).…”

“…Several unfilled polymers have been successfully processed through microinjection moulding [3][4][5][6][7][8][9][10]; for these materials, the processability [3][4], the mechanical properties [5][6][7] and the relationship between properties and micro-structure [8][9][10] were investigated. Often, for specific micro-components, the use of unfilled polymers does not allow to satisfy the thermo-mechanical end-use requirements, and it is necessary to use high-performance polymer compounds.…”

Preparation and characterization of innovative cellulose diacetate/epoxy resin blends modified by isophorone diamine

“…There is growing interest in the environmental protection of the earth because the environmental situation of the earth is worse than that in old times . Although traditional engineered thermoplastics with good mechanical properties, such as polyamide, polycarbonate, polyformaldehyde, poly(butylene terephthalate), and poly(phenylene oxide), can be used as a structural material to bear mechanical stress, these traditional materials are responsible for worsening environmental conditions because of their absence of degradable properties. If all traditional thermoplastics were made from biodegradable polymers, these environmental problems would be solved.…”