Investigation of crystallization behavior of solid and microcellular injection molded polypropylene/nano-calcium carbonate composites using carbon dioxide as a blowing agent

Abstract

This work is aimed at investigating the crystallization behavior of solid and microcellular injection molded polypropylene/nano-calcium carbonate composites. The effects of processing conditions, such as injection speed, mold temperature, and carbon dioxide concentration (used in microcellular injection molding), as well as the filler concentration on the crystal form, crystal orientation, and crystallinity were studied using 2D-wide-angle X-ray diffraction and differential scanning calorimetry. β-form crystals found in the surface layer of injection molded samples under high injection and mold temperature due to stronger shear effect. The orientation degree calculated from the X-ray diffraction images by the Hermans function was high in the surface layer and decreased as the distance from the mold surface increased. The addition of the nano-calcium carbonate filler promoted the formation of β-form crystals but reduced the orientation degree and crystallinity as the nanoparticles disturbed the orientation of the molecular chains. On the other hand, when using the foaming process, the formation of β-form crystals was inhibited and the orientation degree was reduced, but the crystallinity of the samples increased, likely due to enhanced molecular chain mobility from the supercritical carbon dioxide which acted as a plasticizer. The crystallinity of the samples was greater in the surface layer but showed no dependence on the injection speed or mold temperature.

Tuning viscoelastic and crystallization properties of polypropylene containing in-situ generated high aspect ratio polyethylene terephthalate fibrils

“…Neat PP does not show any signs of crystallization over the investigated isothermal treatment period. However, when the PET fibrils are present, the time required for completion of crystallization becomes increasingly shorter as the PET content is increased due to the availability of more heterogeneous crystal nucleation sites [45]. This enhancement in the crystallization rate can be seen clearly in Fig.…”

Non-isothermal crystallization behaviors of poly(lactic acid)/cellulose nanofiber composites in the presence of CO2

“…This minimizes their thermal degradation and maximizes the processing window. Moreover, the presence of CO 2 can also enhance the polymer's crystallization [8,12,[79][80][81]. All these benefits from a CO 2 -assisted polymer process would enable to produce PLA composite with superior mechanical properties [9,67,69,70].…”

Mechanical reinforcement of cellulose nanocrystals on biodegradable microcellular foams with melt-compounding process

“…Therefore, besides the polymeric matrix, the filler used in the foamed composites is another critical factor for the structure and properties of the materials. Diverse inorganic and organic fillers have been reported in the preparation of the foamed composites, for instance calcium carbonate (Chen et al 2013), nanosilica (Gong et al 2012), carbon nanofiber , carbon nanotube (Lim et al 2011), clay (Wong et al 2013), montmorillonite (Zhou et al 2014), lignin (Xue et al 2014) and wood fibers (Faruk et al 2007). As a rigid biomass-based nanoparticle, CNC can be expected to be the promising nanofiller to enhance the performance and provide the possible nucleation effect for the foamed composites.…”