Effects of oxygen and tetravinylsilane plasma treatments on mechanical and interfacial properties of flax yarns in thermoset matrix composites

Abstract

This work is focused on the assessment of the effect of oxygen and polymer plasma tetravinylsilane (pp-TVS) treatments on the adhesion of flax yarns with epoxy and vinylester thermoset matrices. These low temperature plasma processes have been selected as more environmentally friendly alternatives to traditional chemical treatments. Tensile tests performed on single flax yarns revealed a reduction in their mechanical properties after plasma treatments. In particular, a tensile strength reduction of 36.4% was detected after the oxygen plasma treatment using 100W of plasma power. The morphological analysis highlighted that this result is mainly ascribed to the ablation action produced by oxygen plasma process. In the case of pp-TVS, both morphological and Fourier transform infrared spectroscopy analysis (FT-IR) confirmed the presence of a homogeneous tetravinylsilane film on the surface of the yarns. The interfacial adhesion of untreated, oxygen plasma treated, and plasma-polymer coated flax yarns has been determined by single fibre fragmentation test (SFFT). The plasma polymer deposition can produce a significant improvement of the adhesion property of flax yarns with both epoxy and vinylester matrices. An increase of the interfacial shear strength (IFSS) values of 114% and 71% was found after the TVS film deposition in epoxy and vinylester composites, respectively. These results were confirmed by high-resolution micro-CT, photoelasticity analysis and FE-SEM observations.

Surface Modification of Flax Yarns by Enzymatic Treatment and Their Interfacial Adhesion with Thermoset Matrices

“…The spectra appear to be similar, however the main effect produced by the enzymatic treatment was a strong reduction in the bands at around 1736-1742 cm −1 , which can be assigned to the carboxylic ester in the pectin and wax [37] and to the carbonyl C = O stretching of the acetyl groups of hemicellulose [38] and, at 1597 cm −1 , 1514 cm −1 and 1450 cm −1 , of the lignin [8]. It is to be noted that the enzyme preparation used in the present study was not pure, therefore the presence of side enzyme activities cannot be excluded.…”

“…To highlight the changes induced by the enzymatic treatment on the composition of the flax yarns, the FT-IR analysis was carried out on the samples treated using the minimum ( Figure 5) and maximum ( Figure 6) concentration of the Peclyve solution. The spectra appear to be similar, however the main effect produced by the enzymatic treatment was a strong reduction in the bands at around 1736-1742 cm −1 , which can be assigned to the carboxylic ester in the pectin and wax [37] and to the carbonyl C = O stretching of the acetyl groups of hemicellulose [38] and, at 1597 cm −1 , 1514 cm −1 and 1450 cm −1 , of the lignin [8]. It is to be noted that the enzyme preparation used in the present study was not pure, therefore the presence of side Comparing the infrared spectra of the flax yarns enzymatically treated using a 2.5 wt % Peclyve solution for different durations ( Figure 5), it is possible to notice that the longer the treatment time, the greater the removal efficiency of the enzymatic solution.…”

“…The effect of enzymatic treatments on the quality of the yarn/matrix adhesion with epoxy and vinylester matrices was studied by adapting the well-known single fiber fragmentation test (SFFT) to the yarn scale, as already discussed in [8,23,31]. Details of the mould and of the procedure used to manufacture the single yarn composite specimens can be found in [23].…”

“…At least 10 fragmentation tests were carried out for each family of single yarn composites. The experimental procedure has been thoroughly described in previous publications [8,23,31]. A comparison between the critical filament lengths measured for the untreated and the enzymatically treated single yarn composites is shown in Table 6.…”

“…2020, 10, 2910 2 of 17 environmental impact represents a noticeable challenge. With this in mind, many strategies that have been investigated over the years suffer from the need to handle large amounts of chemicals [3][4][5][6] or complex equipment [7][8][9][10][11], which can limit their full industrial exploitation. Another recent approach consists of decorating the fibres' surface with nanostructures to increase the surface area and the stress transfer of the polymer matrix [12][13][14], but this strategy usually involves several processing steps that make it less attractive for industrial applications.…”