Hexagonal boron nitride (BN) platelets are used for fabrication of ultrahigh molecular weight polyethylene (UHMWPE)/BN composite fibers using a flow‐crystallization process. As‐spun fibers are subsequently drawn near the UHMWPE melting temperature. Interfacial crystallization of UHMWPE is observed on the surfaces of the BN platelets. Both X‐ray and Raman spectroscopy analysis of the drawn composite fibers show a significant decrease in the intensity of the signature BN peaks associated with the platelet interlayer spacing, as compared to undrawn samples. This suggests exfoliation of the BN platelets occurs during the fiber hot‐drawing process. Exfoliation of BN platelets is induced due to interfacial stress transfer between both components (i.e., UHMPWE and BN) within the composites. This stress transfer is facilitated by molecular rearrangement of polymer matrix during drawing (i.e., unfolding of the polymer chain). The changes in micro‐ and nanoscale morphologies due to unfolding of the polymer chains as well as simultaneous exfoliation of the BN platelets are fully characterized and show that these structural changes provide insight for understanding the property trends of the fibers.
The effects of different silica grades and elastomer content on interfacial properties, morphology and mechanical properties of polypropylene/silica 96/4 composites modified with added 5, 10, 15, and 20% of poly(styrene-b-ethylene-co-butylene-b-styrene) grafted with maleic anhydride (SEBS-g-MA) were investigated. The iPP/silica/SEBS-g-MA composites were designed by adding four silica fillers differing in size (nano- vs. micro-) and in surface properties (hydrophilic vs. hydrophobic) and SEBS-g-MA that was used as a proven effective impact modifier and compatibilizer simultaneously. The morphology of every composite was a spectrum of several morphologies rather than one exclusive morphology. Good concordance between observed and predicted morphology indicated that the morphology of a particular composite was controlled primarily by interfacial properties. Tensile and impact properties were influenced primarily by competitive effects of a stiff filler and tough SEBS-g-MA elastomer. Increased impact strength and strain at break caused by adding SEBS-g-MA indicated a significant overcoming of the elastomeric toughening effect in relation to the filler’s stiffening effect. 相似文献