Transcrystallization at the interface of polyethylene single-polymer composites

The phenomenon of transcrystallization was studied at the interface of UHMWPE fibers embedded in an HDPE matrix. It was hoped that epitaxial crystallization in such model composites could eventually be used to improve adhesion between these high-strength fibers and the thermoplastic matrix material. Matrix crystallization was induced and accompanied on a specially designed hot stage which made the crystallization front advance slowly along a thermal gradient. Transcrystalline interfacial layers were observed without regard to temperature conditions, but with widely varying dimensions. Lamellar resolution within these layers was achieved by low voltage scanning electron microscopy, and the very beginning of transcrystallization was observed in sample areas where UHMWPE fiber segments were only partially embedded into the HDPE matrix. Lamellar alignment on the fiber surface indicated that transcrystallization in this system was associated with epitaxial nucleation

Resolucao lamelar num novo microscópio eletronico de varredura

Working with low energy electrons (in the range of 1keV), the new scanning electron microscope permits the lamellar (supermolecular) structure of semicrystalline polymers to be observed directly without the need of specimen coating or of any other sample preparation technique. Microscope performance is demonstrated by several examples of high resolution micrographs which show spherulitic, lamellar and fibrilar morphologies developed by the a, b and g phases of PVDF as a function of processing conditions and crystallization temperature. Another example reveals the early stages of transcrystalline layer formation in HDPE reinforced by UHMWPE fibers. Trabalhando com elétrons de baixa energia (na faixa de 1keV), o novo microscópio eletrônico de varredura dispensa a etapa de metalização e permite a observação direta da estrutura lamelar de polímeros semicristalinos, sem a necessidade de preparação de amostras. São apresentados exemplos da morfologia lamelar do PVDF em função das condições de processamento e da temperatura de cristalização, em filmes contendo as fases a, b e g. Um outro exemplo revela o crescimento inicial da camada transcristalina que se formou ao longo de uma fibra de polietileno de ultra-alto peso molecular embutida em matriz de polietileno de alta densidade