No abstract

Thermal ageing of PC/PBT blends and alloys has been studied with dynamic mechanical, calorimetric, and tensile dilatometry tests during creep. The substantial embrittlement occuring in PC/PBT during ageing is tentatively explained in terms of an unusually high densification of the amorphous phase. The phase boundaries have been found to increase in strength during ageing, improving the load bearing properties of the material.

This paper is concerned with the creep behavior of short fiber‐reinforced thermoplastics, especially with regard to the role of fiber orientation. Rectangular samples of low density polyethylene (LDPE) and polycarbonate (PC) containing varying amounts of carbon fibers were prepared by compression and injection molding. The materials were compounded using a technique producing a concentration independent fiber length distribution. The orientation distribution, on the other hand, was found to be strongly influenced by fiber concentration. The creep parameters were measured for both LDPE and PC. The contraction ratio was determined for the PC samples. In the case of LDPE reliable data could not be obtained due to the low modulus of the matrix. The creep properties of the PC and LDPE samples varied significantly with the orientation of the fibers. The creep strain was measured as a function of time for both polymers for different fiber concentrations and orientations. The predictions of the Halpin‐Tsai equation underestimated the experimental strain figures somewhat when the stress direction coincided with that of the fiber orientation. When the stress acted across the fibers the theoretical and experimental results showed satisfactory agreement. A plausible explanation is that incorporation of carbon fibers changes the morphology of the matrix material. We conclude that the contraction ratio is an important measure of the volume and its changes during deformation, especially with regard to its relation to the free volume and similar quantities. We have shown that the necessary data can be obtained, in spite of experimental difficulties even for anisotropic samples.

SynopsisWhen extruding a blend of low density polyethylene (LDPE) and a technical grade of sodium lignosulfonate through a capillary it was observed that LDPE formed fibers in a matrix of the lignosulfonate. With short capillaries and low shear rates, short fibers of LDPE with lengths between 0.5 and 5 m and with diameters in the range 2-20 pm can be produced. Since sodium lignosulphonate is water-soluble, the LDPE fibers can easily be isolated. Such fibers can be used for synthetic wood pulp or in nonwoven types of applications.