Understanding Issues Associated with Using Fiber Length SMCRecyclate in Bulk Molding Compounds with the Aim of Improvingtheir Strengths

摘要

The vast majority of composites materials are non-biodegradable so the annual cost of disposal ison the order of hundreds of millions of dollars. Thermoset matrix composites make up a large portion ofthe non-biodegradable waste. The greatest portions of thermoset waste are sheet molding (SMC) andbulk molding compounds (BMC). Regrinding is currently the most widely used recycling process forSMC. It has been well documented that when recycled (SMC) fibers are used to partially replace virginreinforcement in BMCs the strength of the resulting composite can be decreased by 30% or more.Although the decrease has been well demonstrated, little investigation has been made into the causes forthe reduction. In this investigation reground polyester matrix glass fiber SMC from Mecelec Recyclingwas used as replacement for virgin glass fiber in polyester matrix BMCs. Visual inspection, microscopy,and Fourier infrared transform spectroscopy (FTIR) where used to analyze the fracture surface of therecyclate. Analysis showed a significant portion of the recyclate consists of chips with resin and CaCO3and little glass fiber at the fracture surface.The strength of the BMCs was determined using 3-point flexural tests. Scanning electron andoptical microscopy were used to analyze the fracture of the BMC samples. BMC having a 1 to 1replacement of recycled SMC for virgin fiber had a 68% reduction in strength. Microscopic analysis ofthe facture surface revealed poor bonding between the recycled matrix material and the new matrix. Thebonding problem was particularly bad for recyclate from SMC containing thermoplastic cure shrinkageadditives. Poor bonding between the recycled material and the new matrix is one of the major causes forthe low strength of BMC containing recyclate.To improve the strength the BMC two recyclate surface modification approaches whereinvestigated. One based on plasma treatment and another based on introducing unsaturation to thepolyester chains on the surface of the recyclate. Oxygen Plasma is used to clean and create reactivegroups such as COH, COOH, and OH on the surface of the recyclate. The groups are likely to react withthe components of the new resin improving bonding. Introduction of unsaturation into polyester chainson the surface creates sites for covalent bonding of the recyclate to the new resin chains via the styrenecrosslinker. The goal is to improve polymer-polymer interfacial strength of recycled BMC via covalentbonding between the recyclate and virgin resin.