The last polyolefinic polymer used in our investigation is polypropylene (PP), which ranks among the most consumed polymers globally, is a non-polar thermoplastic semi-crystalline polymer. It is a material that is non-hazardous and non-toxic, which is why it is widely used in the plastics industry.
PP demonstrates good resistance to alkalis and acids, electrical insulation and processing, bending fatigue resistance, and its chemical stability is also great; unlike PPs, its mechanical properties are low; however, its mechanical properties can be improved by reinforcing with fillers .
Sombatsompop and Chaiwattanpipat investigated the difference between the injection molding of pure polypropylene and polypropylene with different contents of glass fibers. They found that the melt temperature is influenced by the presence of glass fibers due to shear heating between polymer-polymer and polymer-glass fibers during the melt flow.
The increase in the melt temperature during the flow appears to be more significant with the reinforcement of glass fibers due to the shear heating in comparison with pure PP. Köpplmayr et al. dealt with the fiber orientation and length distribution and the rheological characterization of glass fiber-reinforced PP.
They prepared three types of blends: compounds with 100% short fibers, 20% long, and 80% short fibers, and 70% long, and 30% short fibers, the wt % of glass fibers in all three compounds was 24 wt %. Their study´s results showed the different rheological behavior depended on fiber content and orientation as well as elongation and shear viscosities, etc.