Long glass fibre reinforced polypropylenes : Fabrication and mechanical properties

The work deals with the fabrication of long glass fibre reinforced polypropylenes and their mechanical properties. Composite materials based on the apparatus called a fibre separating and flying machine, were manufactured in three different ways: compression moulding (Process A), compression moulding with preforming (Process B) and compression moulding under vacuum (Process C). For the mats, various materials were used: two types of glass fibre and one type of aramid fibre for reinforcement. Mechanical properties of composites were evaluated by tensile, bending, Izod impact and a high rate impact test. It was found that preforming does not lower the mechanical properties of the materials, while it noticeably improves their handling properties (process A and B). Comparing samples prepared by processes C and A resulted in the conclusion that applying a vacuum during manufacturing increases the modulus of the composites because flaws caused by voids are less frequent. Another important finding is that for fibre contents of more than 20 vol. %, the mechanical properties of the composites did not increase with increasing fibre content. In order to overcome these tendencies, non separated glass fibre (GF) or aramid fibre (KF) roving (length is ca. 25 mm) were added to the fibre mixture mat during its fabrication in the machine. It was shown that the mechanical properties can be improved by the addition of these fibres, particular KF, which has high toughness and strength.