Application of waste bulk moulded composite (BMC) as a filler for isotactic polypropylene composites

The aim of this study was to produce isotactic polypropylene based composites filled with waste thermosetting bulk moulded composite (BMC). The influence of BMC waste addition (5, 10, 20 wt%) on composites structure and properties was investigated. Moreover, additional studies of chemical treatment of the filler were prepared. Modification of BMC waste by calcium stearate (CaSt) powder allows to assess the possibility of the production of composites with better dispersion of the filler and more uniform properties. The mechanical, processing, and thermal properties, as well as structural investigations were examined by means of static tensile test, Dynstat impact strength test, differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS), melt flow index (MFI) and scanning electron microscopy (SEM). Developed composites with different amounts of non-reactive filler exhibited satisfactory thermal and mechanical properties. Moreover, application of the low cost modifier (CaSt) allows to obtain composites with better dispersion of the filler and improved processability.

Introduction

Reinforced thermoset composites containing inorganic fibres defined as bulk moulding composites (BMC) and sheet moulding composites (SMC) are still applied in automotive and civil engineering industries. The production of these materials in the year 2014 in Europe reached approximately 264 kt [1]. The growing use of fibre reinforced composites (FRP) in industry results in high amount of FRP wastes. Hence, discovering an appropriate area of application for these types of waste material is currently of utmost importance task for scientists [2], [3], [4], [5], [6], [7]. There has been an alarming rise in the amount of FRP waste, and in 2015 only the 304 kt FRP waste will be produced [8].

BMC and SMC materials usually contain polyester resins with short glass fibres (10–25% by volume), colourants, inhibitors, and high amount of fillers, such as calcium carbonate or fire retardant alumina trihydrate [9], [10]. The filler introduction to the matrix should provide the product with sufficient mechanical strength, psychical properties and quality. Fillers such as clay, talc, carbon black, marble dust, glass, wood flour and metals are added to polymers at range from 10 to 50 wt% [10]. The introduction of glass fibres into composites leads to good mechanical properties, while inorganic fillers reduce the product final price [11], [12].

Plastics recycling process involves recovering scrap or waste polymers and reprocessing the material into useful applications [10]. Popular thermoset materials recycling method is their cutting into smaller pieces and grinding to produce very fine powder. As a result of this process, fibrous fraction, with the large particle of the reinforcement fibres, and the polymeric matrix fine powder fraction are recovered [13], [14]. Other method is chemical recycling BMCs and SMCs; however, often a large amount of chemical waste is produced in the process [15], [16], [17]. Therefore, fine powders of these thermosetting polymers can replace calcium carbonate filler in new SMC or BMC [9].

Nevertheless, the introduction of high content of recyclate into polymers may result in processing problems and significant lowering at the mechanical properties [18], [19], [20], [21]. Many from the FRP recyclates could be applied in the construction industry for the non-critical materials, such as partitions, insulation products, fibreboard, pipes, aggregates, cements, asphalts and concretes where shredded waste materials provide required bulk and lower price of product [2]. Moreover, the addition of the thermoset glass fibre recyclates to neat polymers brings environmental benefits of reducing waste amount. Isotactic polypropylene is a popular polymer with good processability, frequently used as matrix for composites. To conclude, the aim of this study was to determine the possibility of bulk moulding compound waste usage as a non-reactive, low cost filler for isotactic polypropylene.