Long glass fibre reinforcement of thermo plastics - Experimental and theoretical results for injection and blow moulding, sheet and pipe extrusion

The paper summarises the main experimental and theoretical results from a long-term programme of research (SAFIRE) to produce and apply long glass fibre compounds to the extrusion of pipes, sheets and profiles and to injection, blow and roto moulding. The overall objective is to obtain the processing speeds associated with short fibre reinforced thermoplastics with the reinforcement efficiencies associated with prepositioned or prepreg thermoset composites. Extrusion and injection moulding are now in the commercial domain, with industrial scale trials underway in the other technologies. Long glass fibres are defined by their ability to form lace-like mat structures within the polymer melt which persist into the solid state. Such structures, which greatly increase both melt strength and solid slate thermo mechanical properties, can be formed with fibre volume concentrations (c) as low as .01. The formation of mat structures depends on the number N of virtual touches per filament. A minimum of around five touches is generally needed. From earlier work N is given as A.c. l/d. A varies with mean fibre orientation in the mat: for the random in-plane case it is approximately 8/pi(2), so that in contrast with typical fibre suspensions (c < d/l) extremely strong particle-particle interactions are involved in the melt state. In the solid state, tensile strength is measured and modelled in terms of number average fibre length (l) and diameter (d), polymer yield strength, fibre distribution efficiency, interfacial shear strength and a specially defined matrix stress magnification factor M. The role of patented fibre management devices in optimising these variables as they appear in the solid state is defined and described.