Recycling of Glass-fibre Reinforced Phenolic Prepreg Waste. Part 2. Milled Prepreg as Functional Filler in PP and PA6

Phenolic resin impregnated glass-fibre prepreg waste was milled and used as reinforcing filler in polypropylene (PP) and polyamide 6 (PA6). Prepreg was particularly suitable to be used as filler in PA6. The fibres were homogeneously distributed during compounding and the addition of 20 wt% prepreg increased the tensile strength of PA6 by 63%, from 52 MPa to 85 MPa. Milled prepreg alone did not significantly increase the tensile strength of PP. However, if compounded together with maleic anhydride grafted polypropylene (PP-g-MA, Epolene G3003) compatibiliser, prepreg can be used as reinforcing filler in PP as well. Addition of 20 wt% prepreg together with 5 wt% Epolene G3003 increased the tensile strength of PP from 26 MPa to 43 MPa. In order to mill the prepreg for compounding with thermoplastics it has to be cured. A 2 kg batch of prepreg had to be cured for at least 2 hours at 200 °C to prevent the phenolic resin from falling off the glass-fibres. Milling should be performed using screens with holes larger than 3 mm in diameter to reduce the amount of prepreg fibres shorter than 2 mm, as they jam the hopper when feeding the recyclate to the extruder. The initial prepreg fibre length is of little importance to the composite mechanical properties, as the fibres are shortened to approximately the same length during compounding.