Low‐temperature compounding of natural fiber/thermoplastic composites via solid‐state shear pulverization (SSSP) is explored for the first time, with a goal of processing temperature‐sensitive natural fibers with high temperature‐melting engineering thermoplastics without fiber degradation. The model study was based on polyamide 6 (PA6) as the matrix material and short flax fibers as the filler materials; flax fiber type was varied to provide a range of comparison. Composite structural characterization was conducted using computer tomography, optical microscopy, and scanning electron microscopy, while mechanical property measurements were performed on injection molded specimens in both tension and bending. SSSP demonstrated robust and effective processing results in model PA6/flax composites, especially when compared with conventional extrusion. SSSP was able to isolate unmodified scutched fibers into individual elementary fibers with minimal scission, and effectively distribute them in the polymer matrix
Development of a Recyclable Flax Fiber Reinforced Polymer Composite
This study compared the mechanical properties of a recyclable flax fiber reinforced polymer composite (FFRP) with a covalent adaptable network (CAN) matrix to an FFRP composite with a conventional (unrecyclable) epoxy resin matrix. The results indicated that composites fabricated via vacuum-assisted resin transfer molding (VARTM) exhibited up to 19% higher tensile modulus and strength compared to those fabricated via hand layup, attributed to reduced air void content and more uniform fiber alignment. Microscopy evidence supported by mechanical property tests revealed superior adhesion of the CAN matrix to flax fibers compared to conventional epoxy resin. Additionally, a solvent-based method was demonstrated for separating fibers from the CAN matrix, facilitating reuse or upcycling.
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- Award ID(s):
- 2050879
- PAR ID:
- 10567256
- Publisher / Repository:
- Zenodo
- Date Published:
- Format(s):
- Medium: X
- Right(s):
- Creative Commons Attribution 4.0 International; Open Access
- Sponsoring Org:
- National Science Foundation
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in situ . The dispersed and distributed filler morphology led to mechanical property enhancements, including 230% and 40% increases in Young's modulus and tensile strength, respectively, compared with neat PA6, at a 20 vol% fiber content. POLYM. COMPOS., 40:3285–3295, 2019. © 2018 Society of Plastics Engineers -
Thermoset polymer composites, known for their outstanding thermal, mechanical, and chemical properties, have found applications in diverse fields, including aerospace and automotive industries. These polymers, once cured, cannot be recycled, making the end-of-life management of these composites very difficult and posing an environmental challenge. Conventional recycling methods are unsuitable for thermosets, forcing their accumulation in landfills and raising environmental concerns. One possible solution to overcome this concern is to use resins or curing agents, or both, made from biodegradable materials. This study explores the fabrication and characterization of polymer composites using a commercially available green curing agent made from biomass. The composite laminates were fabricated using HVARTM (Heated Vacuum Assisted Resin Transfer Molding) process. In this process, heat pads are used to increase the temperature of both the epoxy resin and the plain weave carbon fiber laminate to a desired temperature, providing ease of flow to the resin. Small coupons were cut from the laminate using a water jet machine to study the flexural behavior of the composite in accordance with ASTM testing standards and compared with composite coupons fabricated using conventional epoxy resin.more » « less
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Thanks to its comparable specific mechanical properties to glass fibers, silk is a natural fiber that can be used as an eco-friendly alternative to synthetic reinforcing fibers in composite materials. Compared to natural fibers, especially plant fibers, silk enjoys higher mechanical performances, lower density, and higher elongation even at low temperatures, silk also exhibits other attractive qualities like flame resistance and being naturally continuous. However, silk is known to be prone to moisture absorption from surrounding humid environments. Moisture absorption may alter the silk/resin dynamics during composite manufacturing, and later lead to prem-ature degradation in the composite thermomechanical properties. This study investigates the effect of humidity on silk/resin wettability using two different resins (one epoxy and one vinyl ester) and three different silk architectures. Silk fibers are first exposed to different relative humidity environments. Subsequently, the affinity of the conditioned silk to a set of resins is assessed through measurements of silk/resin contact angle over time. Different silk/resin systems were observed to have contrasting responses to humidity exposure. While some silk/resin systems, such as Ahimsa/epoxy, did not show any change after humidity exposure. Other combinations showed tremendous susceptibility of silk/resin affinity to prior exposure of silk to humidity. For instance, although starting at virtually the same initial hydrophobic contact angle of ~123 degrees, Habotai silk/epoxy samples had contrasting wetting times. While the dried Habotai silk reached full wetting after around 5 minutes, the silk samples exposed to humidity took around 1 hour to reach full im-pregnation. These findings demonstrate the importance of humidity exposure control in silk reinforced composites. Keywords: Natural-Fiber Composites, Contact Angle, Silk, Wettability, Humidity.more » « less
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Both environmental and economic factors have driven the development of recycling routes for the increasing amount of composite waste generated. This paper presents a new paradigm to fully recycle epoxy‐based carbon fiber reinforced polymer (CFRP) composites. After immersing the composite in ethylene glycol (EG) and increasing the temperature, the epoxy matrix can be dissolved as the EG molecules participate in bond exchange reactions (BERs) within the covalent adaptable network (CAN), effectively breaking the long polymer chains into small segments. The clean carbon fibers can be then reclaimed with the same dimensions and mechanical properties as those of fresh ones. Both the dissolution rate and the minimum amount of EG required to fully dissolve the CAN are experimentally determined. Further heating the dissolved solution leads to repolymerization of the epoxy matrix, so a new generation of composite can be fabricated by using the recycled fiber and epoxy; in this way a closed‐loop near 100% recycling paradigm is realized. In addition, epoxy composites with surface damage are shown to be fully repaired. Both the recycled and the repaired composites exhibit the same level of mechanical properties as fresh materials.
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.5281/zenodo.8092082
