Properties of microinjection‐molded polypropylene/graphite composites

Straw Tar Epoxy Resin for Carbon Fiber-Reinforced Plastic: A Review

The massive consumption of fossil fuels has led to the serious accumulation of carbon dioxide gas in the atmosphere and global warming. Bioconversion technologies that utilize biomass resources to produce chemical products are becoming widely accepted and highly recognized. The world is heavily dependent on petroleum-based products, which may raise serious concerns about future environmental security. Most commercially available epoxy resins (EPs) are synthesized by the condensation of bisphenol A (BPA), which not only affects the human endocrine system and metabolism, but is also costly to produce and environmentally polluting. In some cases, straw tar-based epoxy resins have been recognized as potential alternatives to bisphenol A-based epoxy resins, and are receiving increasing attention due to their important role in overcoming the above problems. Using straw tar and lignin as the main raw materials, phenol derivatives were extracted from the middle tar instead of bisphenol A. Bio-based epoxy resins were prepared by replacing epichlorohydrin with epoxylated lignin to press carbon fiber sheets, which is a kind of bio-based fine chemical product. This paper reviews the research progress of bio-based materials such as lignin modification, straw pyrolysis, lignin epoxidation, phenol derivative extraction, and synthesis of epoxy resin. It improves the performance of carbon fiber-reinforced plastic (CFRP) while taking into account the ecological and environmental protection, so that the epoxy resin is developed in the direction of non-toxic, harmless and high-performance characteristics, and it also provides a new idea for the development of bio-based carbon fibers.

Influence of mold cavity thickness on electrical, morphological and thermal properties of polypropylene/carbon micromoldings

In this work, a comparative study on the electrical conductivity (σ) and thermal properties of polypropylene (PP)/carbon microparts with different part thickness (namely, 0.85 and 0.50 mm) is reported. Two different types of carbon filler (i.e., CNT and CB) were adopted to study the efficacy of different carbon fillers in improving the σ of PP/carbon microparts. In general, the σ of 0.85 mm thickness microparts were higher than the 0.50 mm thickness microparts, regardless of the carbon filler type and testing directions. This suggested that higher shearing conditions that prevailed in the microinjection molding (μIM) process were unfavorable for the formation of intact conductive pathways in corresponding moldings, albeit the distribution of carbon fillers turned better with increasing shear rates, as confirmed by morphology observations. The thermal stability of PP/carbon microparts increased with increasing filler concentration. Moreover, the increase of thermal stability was more appreciable for CB-filled microparts which was related to the formation of a CB network structure arising from the use of Ketjenblack® EC-600JD CB that characterized by high surface area (∼1400 m2/g). Differential scanning calorimetry results showed that prior thermomechanical histories (including melt blending and μIM) experienced by the polymer melts had an influence on the thermal behavior of subsequent moldings. Also, there existed a strong shear flow-induced crystallization of polymer chains during μIM because the crystallinity of microparts was higher than that of feed materials.

Effect of mixing conditions and polymer particle size on the properties of polypropylene/graphite nanoplatelets micromoldings

In this study, properties of polypropylene/graphite nanoplatelets (PP/GNP) composites and corresponding micromoldings were systematically studied in terms of filler loading concentrations and mixing methods. PP of different forms, i.e., PP pellets and powders, were adopted to fabricate PP/GNP composites. Additionally, a comparative study of precoating GNP and PP powders using solvent-based solution blending and ultrasonication-assisted mixing was performed. Results showed that PP/GNP composites prepared using powder form PP resulted in at least one order of magnitude higher electrical conductivity than using pellet form PP and further reduced the percolation threshold from 12.5 to 10 wt%, which was related to the state of filler distribution within corresponding moldings. Morphology observations revealed that microparts prepared with powder-PP/GNP composites exhibited less preferential alignment of GNP particles along the flow direction when compared with those molded using pellet-PP/GNP counterparts, which was helpful in improving the overall electrical conductivity for PP/GNP micromoldings.