Gahleitner Markus, Pham Tung, Machl Doris
Borealis Polyolefine GmbH, Innovation Headquarters, St. Peterstr. 25, 4021 Linz, Austria.
Research Institute of Textile Chemistry and Textile Physics, University of Innsbruck, Hoechsterstrasse 73, 6850 Dornbirn, Austria.
Polymers (Basel). 2023 Dec 13;15(24):4692. doi: 10.3390/polym15244692.
Polypropylene-based multiphase compositions with a disperse elastomer phase provide superior impact strength. Making this property indifferent to processing steps requires stabilization of the morphology of these materials. Various approaches have been tested over time, each of which shows limitations in terms of performance or applicability. Using polyethylene (PE) homo- and copolymers capable of silane-based crosslinking as modifiers was explored in the present study, which allows decoupling of the mixing and crosslinking processes. Commercial silane-copolymerized low-density PE (LD-PEX) from a high-pressure process and silane-grafted high-density PE (HD-PEX) were studied as impact modifiers for different types of PP copolymers, including non-modified reference PE grades, LDPE and HDPE. Blends based on ethylene-propylene random copolymers (PPR) and based on impact- (PPI) and random-impact (PPRI) copolymers show improvements of the stiffness-impact balance; however, to different degrees. While the absolute softest and most ductile compositions are achieved with the already soft PPRI copolymer base, the strongest relative effects are found for the PPR based blends. Modifiers with lower density are clearly superior in the toughening effect, with the LD-PEX including acrylate as second comonomer sticking out due to its glass transition around -40 °C. The impact strength improvement found in most compositions (except at very high content) results, however, not from the expected phase stabilization. For comparable systems, particle sizes are normally higher with crosslinking, probably because the process already starts during mixing. Thermoplastic processability could be retained in all cases, but the drop in melt flow rate limits the practical applicability of such systems.
具有分散弹性体相的聚丙烯基多相组合物具有优异的抗冲击强度。要使这种性能不受加工步骤的影响，就需要稳定这些材料的形态。随着时间的推移，人们已经测试了各种方法，但每种方法在性能或适用性方面都存在局限性。本研究探索了使用能够进行硅烷基交联的聚乙烯（PE）均聚物和共聚物作为改性剂，这使得混合和交联过程可以解耦。研究了高压法生产的商业硅烷共聚低密度PE（LD-PEX）和硅烷接枝高密度PE（HD-PEX）作为不同类型PP共聚物的抗冲改性剂，包括未改性的参考PE牌号、LDPE和HDPE。基于乙烯-丙烯无规共聚物（PPR）以及基于抗冲（PPI）和无规抗冲（PPRI）共聚物的共混物在刚度-冲击平衡方面有所改善；然而，程度不同。虽然已经很软的PPRI共聚物基体能够实现绝对最软且最具韧性的组合物，但基于PPR的共混物的相对效果最为显著。密度较低的改性剂在增韧效果方面明显更优，含丙烯酸酯作为第二共聚单体的LD-PEX因其玻璃化转变温度在-40°C左右而格外突出。然而，大多数组合物（非常高含量时除外）的抗冲击强度提高并非源于预期的相稳定。对于可比体系，交联后粒径通常更大，这可能是因为该过程在混合期间就已开始。在所有情况下都能保持热塑性加工性能，但熔体流动速率的下降限制了此类体系的实际应用。
