Effects of processing parameters and material composition on the properties of PP compounds

In recent years, increasing environmental sensitivity, low CO2 emission targets and economic concerns such as fuel economy have pushed automotive manufacturers to produce lighter vehicles. In this context, being lighter and cheaper than metal have increased the usage areas of polymer materials in automotive industry day by day. Polyolefins such as polypropylene and polyethylene have a significant share among automotive polymers due to their strong mechanical properties, easy processability and low density. Polyolefins generally have low physical, mechanical and thermal properties when used without additives. Moreover, they are relatively not inexpensive. Due to this reason, by raw material producers, polyolefins are mostly produced with cheaper additives which also improve their physical, mechanical and thermal properties. The recent increasing trend amongst polyolefin material manufacturers is the production of less dense materials with the same physical, mechanical and thermal properties at lower add-on rates. It has crutial importance to know the effect of different process parameters or different additives on the final product in order to transfer these materials from the laboratory environment to the industrial applications. For this reason, in this study it has been investigated whether the same characteristics can be achieved with low talc content or with nanoclay additive instead of high-talc-doped polypropylene-based raw materials that are used now in serial productions of some big-size exterior trim parts such as bumpers, spoilers and trunk pannels. For this purpose, a kind of polypropylene (PP) copolymer with 30% talc content which is commercially available and being used for the productions of exterior automotive parts for years was taken as a first and reference material. Then, two different PP copolymer respectively with %30 and %20 talc content were taken as alternatives. These two alternative material are still under development and never used for the production of any exterior trim part in automotive industry. So, their process behaviours are unknown. Granules of these three different PP compounds were characterized by several techniques in order to determine their mechanical and thermal properties. For this purpose, thermogravometric analysis (TGA) was used to determine their inorganic additive ratios, melt flow index (MFI) test was performed to characterize their fluidity, density test was run to determine their density. Then the granules of these three PP compunds were molded by an injection machine with fixed mold and barrel temperatures. Then, tensile and bending tests were performed on their specimens in order to determine their strength and modulus values. Impact resistance of the specimens were tested by Izod and Charpy methods to see their energy absorbtion capacities. In order to determine their softening points and heat deflection temperatures heat deflection temperature (HDT) and vicat softening point (VST) tests were made. Differential scanning calorimeter (DSC) was used to measure the enthalpies of specimens related to thermal transitions and chemical reactions and also to determine the temperatures at which these processes occur. With this technique, melting temperature (Tm), crystallization temperature (Tc), melting enthalpy (ΔHm), crystallization enthalpy (ΔHc) and crystalinity (% Xm, % Xc) values were found. On the second step of the study new samples were molded at different mold temperatures and different barrel temperatures by an injection machine to investigate the effects of process parameters on the mechanical and thermal properties. Tensile test, bending test, izod – charpy impact tests, HDT and VST tests were carried out on these samples to see how controlling the process parameters could affect the mechanical propertries. Additionally, melting temperature (Tm), crystallization temperature (Tc), melting enthalpy (ΔHm), crystallization enthalpy (ΔHc) and crystalinity (% Xm, % Xc) values were also found from the DSC spectra to see how controlling the process parameters could affect the thermal properties. Finally, it was aimed to investigate the effect of different additive ratios on mechanical and thermal properties with addition of 1wt.%, 3wt.% and 5wt.% nanoclay in 20wt.% talc filled polypropylene. The XRD analyses were performed to see the dispersion of nanoclay in PP matrix. MFI test, tensile test, bending test, izod – charpy impact tests, HDT and VST tests were carried out on these samples to see how controlling the process parameters could affect the mechanical propertries. Additionally, melting temperature (Tm), crystallization temperature (Tc), melting enthalpy (ΔHm), crystallization enthalpy (ΔHc) and crystalinity (% Xm, % Xc) values were also found from the DSC spectra to see how controlling the process parameters could affect the thermal properties.