Effects of Wet and Dry Treatments on Surface Functional Groups and Mechanical Properties of Flax Fiber Composites

Abstract

Flax fibers have found widespread use in eco-composite materials because of their remarkable mechanical properties compared to glass fibers. However, their low stability limits their use on a larger scale when employed in hot or humid environments. Therefore, the surfaces should be modified before the composite process to provide the best interfacial interactions and increase the dispersion of natural fibers. To tackle this problem, two kinds of modifications can be considered: wet and dry modifications. This research explores different methods to improve the adhesion between flax fibers and the poly lactic acid (PLA) polymer. Morphological and chemical modifications in the presence of acetone, alkali (as a wet modification), and with air atmospheric pressure plasma (as a dry modification) are compared in this research. The results revealed that altering the chemical characteristics on the surface significantly changed the mechanical properties of the final composite. More specifically, the Fourier transform infrared spectroscopy (FTIR) data indicate that wax-related peaks (2850 and 2920 cm−1) were eliminated by both wet and dry treatments. Dynamic mechanical analysis (DMA) results also highlighted that a better bond between the flax fibers and the PLA matrix is obtained with the plasma modification.

Surface Modification of Flax Fibers with TMCTS-Based PECVD for Improved Thermo-Mechanical Properties of PLA/Flax Fiber Composites

“…The smoother appearance observed at high magnitude indicates that the plasma treatment has effectively modified the surface characteristics of the fibres. These findings align with our previous research [28] on the impact of plasma treatment on the removal of natural waxy substances from the fibres, indicating the treated state of the samples. Thus, the results reinforce the efficacy of plasma treatment to replace conventional wet methods to "clean" and/or functionalize the surface of natural fibres in dry conditions.…”

“…Upon subjecting the flax fibre to plasma treatment using N2 gas some transformations in the ATR-FTIR spectra were observed (zoom (a)). Remarkably, the characteristic peaks associated with wax at approximately 2915 cm −1 and 2850 cm −1 , which correspond to the asymmetrical and symmetrical stretching of CH2 groups, were effectively eliminated in agreement with previous findings [28]. In addition, the emergence of a distinct peak around 1720 cm −1 signified the presence of a carbonyl group (zoom (b)).…”

“…Remarkably, all flax/PLA composites exhibit a decrease in storage modulus around the glass transition temperature (Tg), followed by a subsequent increase above 80 • C, attributed to cold crystallization. This phenomenon aligns with prior research [28] where flax fibre was employed as a nucleator to augment the crystallization capability of PLA composites.…”

“…The selection of TMCTS as the coating material is based on its exceptional advantages over other coatings. It possesses transparency, hardness, and compatibility with organic compounds, allowing for effective bonding with different substrates and enhancing mechanical performance and long-term durability [28]. Additionally, TMCTS is non-toxic, making it environmentally friendly, and its plasma polymers demonstrate desirable properties, including hardness, low gas permeability, and high chemical resistance [29].…”

The Influence of the Chemical Composition of Flax and Hemp Fibers on the Value of Surface Free Energy

“…In spinning processes, they reduce the coefficient of friction, facilitating the formation and thinning of a stream of parallelly arranged fibers [ 18 , 19 ]. Various methods of fiber processing lead to partial removal of waxes and fats, but may lead to better fiber adhesion [ 51 , 52 , 53 ]. The evaluation of the content of waxes and fats in the flax fiber of the MODRAN and NIKE variety showed that the degumming of the decorticated fiber caused the partial removal of waxes and fats in the fiber as a result of the combined action of water and ultrasound.…”