Influence of Polymer Matrices on the Tensile and Impact Properties of Long Fiber-Reinforced Thermoplastic Composites

This study aims at an innovative sample preparation strategy for fiber reinforced thermoplastic (FRTP) composites analyzed via polarized optical microscopy to visualize the crystalline structure of the matrix resin. Investigating the structure is relevant for understanding the relationship with the mechanical properties. In general, polarized optical microscopy is a powerful technique for visualizing polymer crystalline structures at samples sliced into thin sections below 30 μm. However, analyzing FRTPs remains challenging in absence of suitable methods for the preparation of thin sections owing to the embedded fibers. Herein, the preparation of appropriately thin sections in a novel sequence of steps is shown that may generically be applied to FRTPs. Four different types of FRTPs with major matrix resins (GF/PBT, CF/PA6, CF/PEEK and GF/PP) were successfully processed to thickness of 5 μm or below without fiber loss, resin breakage or delamination between fiber and resin demonstrating the utility of the developed method, which is the significant outcome of the study. To the best of our knowledge, the subsequently obtained polarized optical microscopic images for the first time visualized the crystalline structure of the matrix resin revealing nucleation of crystals from the fiber surface and effects of mold flow on the crystallization behavior.Highlights Thinning of fiber reinforced thermoplastics to thickness of 5 μm or below. Thinning achieved despite fiber volume at industrial applications level. Sample preparation ensures ideal conditions for polarized optical microscopy. Visualization of crystalline structure of the matrix resin for the first time. Potential advancement for spectroscopic and electron microscopic analyses.

Section: Introductionmentioning

confidence: 99%

An innovative sample preparation strategy to visualize the crystalline structure of fiber reinforced thermoplastic composites by polarized optical microscopy

Yoshida,

Furushima,

Yamamoto

et al. 2024

Effects of fiber characteristics on tensile and impact properties of long fiber reinforced High‐Density Polyethylene

Jiang,

Wang,

Zhou

2024

Due to the requirements of high stiffness and impact strength of HDPE pipes, in this article, long fiber reinforced HDPE were developed and the effects of fiber length, volume fraction, types, and matrix/fiber interface on the mechanical properties were investigated. Tensile properties, notched impact strength, as well as microstructures were tested. The results showed that fibers increased the tensile strength, modulus, and impact strength, but decreased their plastic deformation. Larger fiber fraction indicates more fibers are involved in load bearing, but easy agglomeration. With ascending fiber length, tensile, and impact strength first increased and then decreased, whereas tensile modulus first increased and then maintained an almost constant value. Carbon fibers showed no advantages over glass fibers and basalt fibers in reinforcing HDPE due to the relatively poor interface bonding strength. Interface modification with KH550 improved the mechanical performance of composites, but the enhancement was limited. More effective methods should be developed for better performance.Highlights Fiber increases strength and modulus, but decreases plastic deformation. Critical fiber length for basalt LFT is 2.6 mm obtained from SEM. Larger fiber volume and length lead to agglomerations. Difference in BF, CF, and GF reinforced HDPE is determined by interface. Interface modification enhances mechanical properties of LFT but limited.

Cross‐referenceable microscopic and micro‐spectroscopic analysis of fiber reinforced thermoplastics

Yoshida,

Furushima,

Okino

et al. 2024

This study aims at the assessment of damage on crystallinity of fiber reinforced thermoplastic (FRTP) composites resulting from mechanical polishing to demonstrate a novel methodology enabling comprehensive crystalline structural characterization. Investigating the crystalline structure is relevant for understanding the relationship with the mechanical properties. In a previous study, FRTPs have successfully been processed to the thickness of 5 μm or below via an innovative polishing strategy, which for the first time visualized the crystalline morphologies by polarized optical microscopy. Analyzing these sections via micro‐Raman and micro‐infrared spectroscopies facilitate the quantification of these structure. However, no study reports on the correct interpretation of FRTP data appropriately considering the damage resulting from mechanical polishing to date. Herein, we report fundamental knowledge on this aspect via detailed Raman micro‐spectroscopic investigations to demonstrate our novel strategy. Four types of FRTPs with major matrix resins (GF/PBT, CF/PA6, CF/PEEK and GF/PP) were analyzed and the damage on both polished cross‐sections, prepared by traditional process, and the thin sections was confirmed to be approx. 1%–2% crystallinity, which solidified the credibility of the obtained analytical data. Then, the newly established methodology of ‘cross‐referenceable microscopic and micro‐spectroscopic analyses for FRTPs’ was applied for comprehensive crystalline structural characterization.Highlights Cross‐sectioning and thin‐sectioning of FRTPs. Evidencing of damage on the crystallinity resulting from mechanical polishing. Equations to convert Raman spectral data into crystallinity. Strategy for considering the anisotropy of Raman measurements. Practical application of novel microscopic and micro‐spectroscopic strategies.