The morphological evolution and β-crystal distribution of isotactic polypropylene with the assistance of a long chain branched structure at micro-injection molding condition

Influence of Injection Molding Parameters and Distance from Gate on the Mechanical Properties of Injection-Molded Polypropylene

This publication deals with the study of the mechanical properties of injection-molded polypropylene parts depending on the process parameters and the distance from the gate location in which the mechanical properties were investigated. Due to the fact that the mechanical properties of injection-molded parts are not the same at all locations, this research was designed to investigate the inhomogeneity of the properties of injection-molded parts along the length of the product. The inhomogeneity is affected by various influences, including distance from the sprue mouth, melt and mold temperature, injection pressure, crystal structure, and others. It was demonstrated that mechanical properties are not uniform over the entire injected product. Contrary to popular belief, mechanical properties can vary along the flow length due to uneven cooling and process parameters. Injection pressure and mold temperature significantly affect the mechanical properties of the injection-molded parts. The limiting injection pressure is 40 MPa and the mold temperature is 40 °C. The difference in individual spots in an injected article was up to 37%. Changes in mechanical properties are closely related to changes in morphology (crystallinity measured by DSC) caused by different injection molding process parameters. As is evident from the aforementioned results, the possible benefits of this work for injection molding of polymer products are apparent. Suitably chosen gate location, surface of the cavity, and process parameters can ensure targeted improvement of mechanical properties in stressed parts of a product.

The Effects of Lignin on the Thermal and Morphological Properties and Damage Mechanisms after UV Irradiation of Polypropylene Biocomposites Reinforced with Flax and Pine Fibres: Acoustic Emission Analysis

This study investigates the impact of lignin on the durability and performance of polypropylene-based biocomposites (PP-flax and PP-pine) under environmental stresses such as UV radiation and moisture. The findings indicate that pine fibres, with their higher lignin content, are significantly more resistant to thermal degradation than flax fibres. Differential scanning calorimetry (DSC) showed that lignin influences crystallinity and melting temperatures across the composites, with variations corresponding to fibre type. Acoustic emissions analysis revealed that increasing the lignin content in pine fibres effectively reduces surface microcracks under UV exposure. Overall, these results underscore the importance of fibre composition in improving the performance and longevity of biocomposites, making them better suited for durable construction applications.

Influence of Process Parameters on the Morphologies of Micro-Injection Molded Polyformaldehyde Parts

The morphologies of micro-injection molded parts are influenced by the process parameters. In this paper, the influence of injection speed, mold temperature and melt temperature on the morphologies of micro-injection molded polyformaldehyde (POM) parts with different thicknesses were investigated by a single factor experimental method; the morphological structure of the parts was characterized by polarized light microscopy. The scale effect on the crystallization behavior and internal morphology of micro-injection POM parts was analyzed. The results indicated that the scale effect had a great influence on the hierarchical morphology in the thickness direction of the parts. The micro-parts with a thickness of 1.0 mm showed a skin-core structure including the skin layer, fine grain layer, oblate spherulite, and spherulite core layer, and the micro-parts with a thickness of 0.2 mm showed a skin-core structure with the skin layer, fine grain layer, and the spherulite core layer, and a larger thickness ratio of the spherulite core layer. As injection speed, mold temperature and melt temperature increase, the fine grain layer gradually disappears and the size of core spherulite tends to become larger, the thicknesses of the skin layer of all the micro-parts decrease and that of the 0.2 mm micro-parts decreases significantly.

Controlling crystal polymorphism of isotactic poly(1-butene) by incorporating long chain branches

Isotactic poly(1-butene) (iPB-1) is a high performance plastic with outstanding properties, such as flexibility, superior creep, environmental stress cracking and abrasive resistance. However, it exhibits a complex crystal polymorphism and polymorphic transformation behavior, which has limited its commercial development. In this paper, the incorporation of long chain branches (LCBs) causes coil contraction in the melt, which favors the direct melt-crystallization of form III that was generally crystallized from solutions and made of unconventional highly twined lamellae. Consequently, low-to-moderately branched iPB-1 samples as-crystallize from the melt into mixtures of form II and form III by compression-molding and fast cooling of the melt to room temperature, and the fraction of crystals of form III (fIII) increases with increasing concentration of LCBs, whereas highly branched samples can as-crystallize into pure form III with uniform crystal size distribution. The corresponding thermomechanical properties can be modified by controlling fIII.

Flow and Thermal History Effects on Morphology and Tensile Behavior of Poly(oxymethylene) Micro Injection Molded Parts

The micro injection molding process is a rapidly growing area in plastics processing technology. In this process, the polymer is exposed to both high shear rates and large thermal gradients. In view of the versatility of the process, both commodity and engineering polymers have been used in micro injection molded products. In the present work, poly(oxymethylene) (POM), a partially crystalline engineering polymer, was employed to evaluate the relationships between processing conditions, on one hand, and the morphology and properties of the final part, on the other hand. An unsymmetrical mold cavity to make parts in the form of stepped plaques was used in the study. This resulted in substantial differences in morphology, crystallinity and shrinkage of the zones of different constant thicknesses in the micro parts. Depending on the molding conditions and the location on the micro-part, the microstructure can display up to five crystalline layers. Of particular interest, shish-kebab crystalline structures were observed within the skin of the step with the smallest thickness. Differential scanning calorimetry (DSC) tests are used to distinguish between the melting points of the shish and kebab components of this particular structure. The degree of crystallinity as determined by wide angle X-ray diffraction (WAXD) and shrinkage across the thickness were also found to be highest in the step with the smallest thickness.