Synergistic effects of micro and macro-sized palm kernel shell fillers on the tensile properties of HDPE composites

In this study, high-density polyethylene (HDPE) composites reinforced with palm kernel shell (PKS) fillers of mixed particle sizes were prepared using melt-extrusion compounding. A 5-ton hydraulic hot press machine was employed to fabricate samples for tensile testing, with a focus on understanding the influence of varying filler sizes on the mechanical properties of the HDPE/PKS composite. The results demonstrated that the incorporation of larger PKS particles (PKSL) had a detrimental effect on the tensile properties, with increasing PKSL content leading to significant reductions in tensile properties. For example, at 7.5 wt% PKSL, the elastic modulus (E) decreased by approximately 18%, yield strength by 37%, ultimate tensile strength (UTS) by 24%, stress at failure by 29%, and total elongation by 62%. Similar trends were observed for composites containing 15 wt% and 22.5 wt% PKSL. Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) were employed to assess the melting temperature ranges and thermal stability of the composites, respectively. Scanning Electron Microscopy (SEM) provided insights into the failure mechanisms, revealing weak filler-matrix interfacial bonding with larger particles, resulting in debonding and ultimately compromising the tensile properties of the composite.

Methods
The dataset for both 250-micron and 1mm particle sizes of palm kernel shells (PKS) was collected through micrographic analysis. An ImageJ software was used to measure the particle lengths from micrographs of the PKS. The data collected through ImageJ was exported as CSV files for both particle sizes. the data was then imported into Excel, where  random numbers were generated based on the mean and standard deviation of the measured data. 

For the FTIR analysis, the data was obtained using an ATR-FTIR machine in the lab. The machine provided transmittance and wavenumber values for the PKS, which were then used to analyze the chemical composition of the material.

本研究采用熔融挤出复合法，制备了混合粒径棕榈仁壳（palm kernel shell, PKS）填料增强的高密度聚乙烯（high-density polyethylene, HDPE）复合材料。使用5吨液压热压机制备拉伸测试试样，重点探究填料粒径变化对HDPE/PKS复合材料力学性能的影响。结果表明，引入较大粒径的PKS颗粒（PKSL）会对拉伸性能产生不利影响，随着PKSL添加量的增加，复合材料的拉伸性能显著下降。例如，当PKSL添加量为7.5 wt%时，弹性模量（E）下降约18%，屈服强度下降37%，拉伸极限强度（ultimate tensile strength, UTS）下降24%，断裂应力下降29%，总延伸率下降62%。在添加15 wt%和22.5 wt% PKSL的复合材料中也观察到了相似的变化趋势。本研究分别采用差示扫描量热法（Differential Scanning Calorimetry, DSC）与热重分析（Thermogravimetric Analysis, TGA）表征复合材料的熔融温度范围与热稳定性能；通过扫描电子显微镜（Scanning Electron Microscopy, SEM）分析复合材料的断裂机制，结果显示较大粒径颗粒的填料与基体界面结合较弱，易发生脱粘现象，最终损害了复合材料的拉伸性能。

方法
本研究针对250 μm与1 mm两种粒径的棕榈仁壳（PKS），通过显微图像分析采集数据集。使用ImageJ软件对PKS的显微图像进行颗粒长度测量，将两种粒径的测量数据导出为CSV格式文件。随后将数据导入Excel，基于实测数据的均值与标准差生成随机数。

对于衰减全反射傅里叶变换红外光谱（ATR-FTIR）分析，实验数据通过实验室的ATR-FTIR仪器获取，该仪器可输出PKS的透过率与波数数据，用于分析材料的化学组成。