Liparoti Sara, Salomone Rita, Speranza Vito, Pantani Roberto
Department of Industrial Engineering, University of Salerno, Via Giovanni Paolo II, 132, 84084 Fisciano, SA, Italy.
Polymers (Basel). 2024 Jan 26;16(3):337. doi: 10.3390/polym16030337.
A more sustainable use of plastic parts makes it necessary to replace current plastic parts with recyclable components, also allowing the modulation of the part properties through the process. Injection molding is one of the most widely used technologies for obtaining rigid plastic parts, so it is crucial to understand how to tailor properties by adopting the correct processing conditions. One way is to perform annealing steps directly inside the mold: in-mold annealing improves the structural integrity and durability of the material, reduces defects, increases the resistance of parts against certain chemicals, reduces wear and tear, increases ductility, and lowers brittleness. In this work, several in-mold annealing steps were conducted, changing the mold temperature and annealing duration selected on the basis of the half crystallization time of the adopted isotactic polypropylene. The typical molded part morphology, composed of oriented layers at the surface, transition zones, and spherulitic core, is strongly affected by in-mold annealing. In particular, the thickness of the oriented layer, which forms in the early phase of the process, decreases, and the spherulites increase in size. Concerning mechanical behavior, the orientation degree mostly determines the elastic modulus value close to the surface, whereas the conditions under which crystallization occurs determine the modulus in the core.
更可持续地使用塑料部件需要用可回收部件取代当前的塑料部件，这也使得通过该工艺调节部件性能成为可能。注塑成型是获得刚性塑料部件最广泛使用的技术之一，因此了解如何通过采用正确的加工条件来调整性能至关重要。一种方法是直接在模具内部进行退火步骤：模内退火可改善材料的结构完整性和耐久性，减少缺陷，提高部件对某些化学品的耐受性，减少磨损，增加延展性，并降低脆性。在这项工作中，进行了几个模内退火步骤，根据所采用的等规聚丙烯的半结晶时间来改变模具温度和退火持续时间。典型的模制部件形态由表面的取向层、过渡区和球晶核心组成，模内退火对其有很大影响。特别是，在工艺早期形成的取向层厚度减小，球晶尺寸增大。关于机械性能，取向程度主要决定靠近表面处的弹性模量值，而结晶发生的条件决定核心处的模量。
