Melt transcrystallization of polyethylene on high modulus polyethylene fibers

Abstract

SynopsisA polytheylene composite was prepared and tested. It consisted of a high-density polyethylene (HDPE) matrix and uniaxial gel-spun high-modulus PE fiber. Aided by the similarity between matrix and fiber, transcrystallization of HDPE melt on the PE fiber surface was generated. Nucleating agents were not employed. The transcrystalline growth of HDPE on the PE fiber surface was found to consist of an inner and an outer zone. The inner zone, 2-3 pm thick, is composed of HDPE crystals nucleated on the PE fiber surface. Photomicrographs showed a well-defined region of row-nucleated HDPE on the surface of PE fiber. This means the fibrils of HDPE were found to grow out from the PE fiber axis and HDPE crystallites are oriented in planes perpendicular to the PE fiber axis. The fiber in the composite induced the transcrystalline growth of HDPE on the PE fiber surface at higher temperature than on cooling the melt. For 36 wt% fiber, the increase was 2.5"C, also resulting in -10% more crystals. Crystallization of a composite with 50 wt% fiber at 124°C involved two steps: The first a fast transcrystallization of HDPE on the PE fiber surface followed by the bulk crystallization of the HDPE.

Oriented structure of PP/LLDPE multilayer and blends films

“…It consists in a lamellar growth of one polymer nucleated from the interface (lamellae perpendicular to the interface). It may result from various reasons: (1) polymers [12]; (2) the presence of stresses at the interface causing many nucleating sites [13]; and (3) crystal unit cell or chemical structure similarities between the two polymers [5,14,15]. Polyolefins blends and multilayer films are widely used in flexible packaging.…”

Modelling of polypropylene fibre-matrix composites using finite element analysis

“…The contribution of each element of the composite model was taken into consideration according to Equations (2) and (3). This resulted in better estimates for the elastic moduli of various composites, than the estimates of other models, such as the rule of mixture [20,21] and the Halpin-Tsai [22] (H-T) equation.…”

“…After this optimum level, the stress concentration increased at the fibrematrix interface and in the matrix resulting in composite failure at lower stress, as predicted by FEA. The simplest model for the micromechanics of fibre composites is that of Cox [20,21] that is used in an analysis known as classical shear lag, where the theory required that simplifications are made. The assumptions are: 1.…”

Morphology, Thermal and Mechanical Properties of Poly(propylene) Fibre‐Matrix Composites

“…This can be explained by the assumption that PP fibres act as a nucleating agent for the matrix, which would increase both the crystallization nucleation and the number of spherulites nucleated in the matrix phase. [16,25,26] Note the fibre PP crystallised separately from the matrix, since there was insufficient time for intermixing of the two components. A second melting scan Figure 1(c) showed that the two melting peaks were retained, though the higher fibre melting peak was less sharp.…”

“…A slight plateau in the loss modulus in the rubbery domain can be observed between T g and T m . The small a-relaxation peak appears as a shoulder and can be attributed to a lamellar slip mechanism and rotation in the crystalline phase [26] as the incorporation of the fibres in the matrix considerably enhanced stiffness and strength of the composites. The position of the b-relaxation or T g is shifted to slightly higher temperatures with increasing fibre diameter in the composites.…”