Modification of polypropylene properties through additivation and formulation improvements
Nucleators (nucleating agents) have improved the properties of commodity plastics such as polypropylene (PP), where its properties are now comparable with those of engineering plastics such as polycarbonate and acrylonitrile butadiene styrene. 1 This has enabled commodity plastics to be used in more demanding applications such as baby feeding bottles that need to be sterilized by boiling water and disposable food containers that need very high flow and fast cycle time during production. In order to achieve the targeted performance of the various applications, a higher dosage of nucleator can be used to further enhance the nucleation of PP. However, this would come at the expense of add-on costs since the nucleator is probably the most expensive ingredient (in dollars per kg) in PP stabilization. In this research a non-nucleating coadditive, sodium myristate (NaMy), added into a DHT4A-stabilized homopolypropylene with Milliken Chemical’s Hyperform® HPN68L nucleator (disodium salt of bicycle (2.2.1) heptane-2,3-dicarboxylic acid 2 ) via dry blending was found to be able to boost the nucleation efficiency of HPN68L in PP, thus improving the polymer’s physical properties without increasing the HPN68L concentration. Subsequent tests showed that the optimum blend ratio of 300 ppm HPN68L and 200 ppm NaMy had improved the 300 ppm HPN68L-nucleated PP peak crystallization temperature ( T c ) by 2.3°C, clarity by 20.3%, cycle time by 8.9%, heat deflection temperature by 4°C and flexural modulus by 60 MPa. It was discovered that the improvements were due to improved dispersion of the nucleator in PP. Further investigation also demonstrated that coating of NaMy onto HPN68L via a novel coating technique was better than the dry blend method in improving dispersion of the nucleator, resulting in the best nucleation performance.