In the automotive industry the requirement of using recycled plastics material is encouraged by European directives. In fact, particularly in the polyolefin sector large amounts of regrind materials are being used. The scrap ratio depends a lot of the sourcing of the regrind. In most cases manufacturers that use off grade, regrind material will make sure its single source regrind supplier , which is in its turn a challenge as the volumes offered are not constant. Off grade or regrind is a byproduct and as such not an intentional product to be produced!
While in the polyolefines sector intrinsic property differences caused by regrind can be influenced more easily by appropriate selection of additives and/ or other resins, it becomes more trickier for the higher end polar thermoplastics like e.g PC/ABS.
In order to make a decision if a regrind / off grade material has a negative effect statistical analysis and multi variable regression helps a lot to determine which factor is really the cause of the problem. Too often different views, impressions, thoughts, all equally valid, are being raised as possibilities but it needs to be supported by statistically significant data.
So, with regard to the PC + ABS problem following strategy could be considered:
- Measurement of the vicat or HDT between a good and a bad lot can already learn a lot if the material has been degraded or behaves differently. It’s a small quickly done test.
- The supplier of raw materials should provide statistical data of the off grade material and of other material that has being offered and prove the material is single source. E.g. I know of applications in the automotive where polyamide regrind is used in certain glass reinforced grades where the sourcing is solely polyamide grade derived from the fiber process. In this case the addition of such regrind can be monitored and the risk limited within the statistical tolerance.
The same could work for PC, I know of applications that only allow CD polycarbonate of one single source…. However, it still remains a risk and taken into consideration the suppliers position of this raw material scrap ratios up to 10 % are common practice over that level the risk is too big, the claims to large, and I know as I used to work for one of the largest plastics recyclers in the European area.
What percentage of talcum is used in this PC + ABS blend? Typically talcum is more used in filled polypropylene materials in automotive while, at least in Europe it’s not used a lot in polar alloys. One of the potential problems being that the intrinsic metal content in talcum, like iron, provokes / catalysis thermal decomposition of the polycarbonate, which results in deterioration of the mechanical properties. It will have an effect of the surface, depending on the particle size distribution and the dispersion efficacy of the first compounding step. It does reduce scratch resistance to my experience.
