Liparoti Sara, Speranza Vito, Titomanlio Giuseppe, Pantani Roberto
Department of Industrial Engineering, University of Salerno, via Giovanni Paolo II, 132-84084 Fisciano (SA), Italy.
Institute of Polymers, Composites and Biomaterials (IPCB), The National Research Council (Cnr), Via Previati 1/C, 23900 Lecco (LC), Italy.
Polymers (Basel). 2020 Feb 5;12(2):341. doi: 10.3390/polym12020341.
The tailoring by the process of the properties developed in the plastic objects is the more effective way to improve the sustainability of the plastic objects. The possibility to tailor to the final use the properties developed within the molded object requires further understanding of the relationship between the properties of the plastic objects and the process conduction. One of the main process parameters that allow adjusting the properties of molded objects is the mold temperature. In this work, a thin electrical heater was located below the cavity surface in order to obtain rapid and localized surface heating/cooling cycles during the injection molding process. An isotactic polypropylene was adopted for the molding tests, during which surface temperature was modulated in terms of values and heating times. The modulation of the cavity temperature was found able to control the distribution of relevant morphological characteristics, thus, properties along the sample thickness. In particular, lamellar thickness, crystallinity distribution, and orientation were analyzed by synchrotron X-ray experiments, and the morphology and elastic modulus were characterized by atomic force microscopy acquisitions carried out with a tool for the simultaneous nanomechanical characterization. The crystalline degree slightly increased with the cavity temperature, and this induced an increase in the elastic modulus when high temperatures were adopted for the cavity surface. The cavity temperature strongly influenced the orientation distribution that, on its turn, determined the highest values of the elastic modulus found in the shear layer. Furthermore, although the sample core, not experiencing a strong flow field, was not characterized by high levels of orientation, it might show high values of the elastic modulus if temperature and time during crystallization were sufficient. In particular, if the macromolecules spent adequate time at temperatures close to the crystallization temperature, they could achieve high levels of structuring and, thus, high values of elastic modulus.
通过该工艺对塑料制品所形成的性能进行定制，是提高塑料制品可持续性的更有效方法。根据最终用途定制模制物体内部所形成的性能，需要进一步了解塑料制品性能与工艺传导之间的关系。能够调节模制物体性能的主要工艺参数之一是模具温度。在这项工作中，在型腔表面下方放置了一个薄电加热器，以便在注塑过程中获得快速且局部的表面加热/冷却循环。采用等规聚丙烯进行模塑试验，在此期间，根据温度值和加热时间对表面温度进行调制。发现型腔温度的调制能够控制相关形态特征的分布，进而控制沿样品厚度方向的性能。具体而言，通过同步加速器X射线实验分析了片晶厚度、结晶度分布和取向，并使用同时进行纳米力学表征的工具通过原子力显微镜采集来表征形态和弹性模量。结晶度随型腔温度略有增加，当型腔表面采用高温时，这会导致弹性模量增加。型腔温度强烈影响取向分布，而取向分布又决定了在剪切层中发现的弹性模量的最高值。此外，尽管样品芯未经历强流场，其取向程度不高，但如果结晶过程中的温度和时间足够，它可能会显示出较高的弹性模量值。特别是，如果大分子在接近结晶温度的温度下花费足够的时间，它们可以实现高水平的结构形成，从而获得较高的弹性模量值。
