Mechanical Properties of Flax-Polypropylene Composites from Dry Flexible Towpregs: Influence of Radial Position of Flax Fibers in the Towpreg

ABSTRACT

The radial position of the flax fibers as reinforcement and polypropylene (pp) fibers as matrix was altered using friction spinning in three distinctive sequences from core to sheath, namely, (a) pp-flax-flax-pp (PFFP), (b) flax-pp-flax-pp (FPFP), and (c) flax-flax-pp-pp (FFPP). Interestingly, at the towpregs stage, PFFP demonstrated higher tensile characteristics than FPFP and FFPP. The towpregs were consolidated to yield three unidirectional composites (UDCs), namely, UDC-PFFP, UDC-FPFP, and UDC-FFPP, using compression molding. The tensile strength of the composites (${\sigma }_{\mathrm{U}\mathrm{D}\mathrm{C}-\mathrm{F}\mathrm{F}\mathrm{P}\mathrm{P}}>\hspace{0.17em}{\sigma }_{\mathrm{U}\mathrm{D}\mathrm{C}-\mathrm{F}\mathrm{P}\mathrm{F}\mathrm{P}}>\hspace{0.17em}{\sigma }_{\mathrm{U}\mathrm{D}\mathrm{C}-\mathrm{P}\mathrm{F}\mathrm{F}\mathrm{P}}$) was contrary to the breaking load (f) of the corresponding towpregs ($f_{\mathrm{F}\mathrm{F}\mathrm{P}\mathrm{P}}<\hspace{0.17em}{f}_{\mathrm{F}\mathrm{P}\mathrm{F}\mathrm{P}}<\hspace{0.17em}{f}_{\mathrm{P}\mathrm{F}\mathrm{F}\mathrm{P}}$) which necessitated the current investigation. Remarkably, the UDC with the lowest tensile as well as interlaminar shear strength i.e. UDC-PFFP, yielded the maximum energy absorption in Charpy and Notch impact tests. In the towpreg, the flax fibers when placed at the core position, slid over each other resulting in poor strength in FFPP while post-curing the pp matrix impregnated the core flax fibers in UDC-FFPP, resulting in the highest strength amongst the three UDCs in tensile and flexural modes. Micro-computed tomography (µCT) was carried out to confirm the same. Thus, the user can select the requisite fiber-matrix radial positions within towpreg to suit the ultimate applications.

摘要

使用摩擦纺纱以三种不同的顺序从芯到鞘改变作为增强体的亚麻纤维和作为基体的聚丙烯（pp）纤维的径向位置，即:（a）聚丙烯-亚麻pp（PFFP），（b）亚麻-聚丙烯-亚麻聚丙烯（FPFP）和（c）亚麻-亚麻pp pp（FFPP）. 有趣的是，在towpregs阶段，PFFP表现出比FPFP和FFPP更高的拉伸特性. 使用压缩模塑，将丝束预浸料固结以产生三种单向复合材料（UDC），即UDC-PFFP、UDC-FPFP和UDC-FFPP. 复合材料的拉伸强度（σ_（UDC-FFPP）>σ_. 值得注意的是，具有最低拉伸强度和层间剪切强度的UDC，即UDC-PFFP，在夏比和缺口冲击试验中产生最大能量吸收. 在towpreg中，当放置在芯部位置时，亚麻纤维彼此滑动，导致FFPP中的强度差，而在后固化时，pp基体将芯部亚麻纤维浸渍在UDC-FFPP中，导致在拉伸和弯曲模式下三种UDC中的强度最高. 进行了显微计算机断层扫描（µCT）以证实这一点. 因此，用户可以在towpreg内选择必要的纤维基体径向位置，以适应最终应用.

KEYWORDS:

• Flexible towpreg
• natural flax fibers
• radial position
• damage mechanics
• mechanical testing
• Micro-CT

关键词:

• 柔性拖带
• 天然亚麻纤维
• 径向位置
• 损伤力学
• 机械测试
• 微型CT

Acknowledgement

The authors gratefully acknowledge the contribution of Mr. Bhanu Bharadwaj and Mr. Abhinav Gudala toward their assistance in the production of composites.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethical approval

We confirm that all the research meets ethical guidelines and adheres to the legal requirements of the study country. The research does not involve any human or animal welfare-related issues.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/15440478.2022.2120591