Green Sound-Absorbing Composite Materials of Various Structure and Profiling

This article presents thermoplastic sound-absorbing composites manufactured on the basis of renewable raw materials. Both the reinforcing material and the matrix material were biodegradable and used in the form of fibers. In order to mix flax fibers with polylactide fibers, the fleece was fabricated with a mechanical system and then needle-punched. The sound absorption of composites obtained from a multilayer structure of nonwovens pressed at different conditions was investigated. The sound absorption coefficient in the frequency ranging from 500 Hz to 6400 Hz was determined using a Kundt tube. The tests were performed for flat composites with various structures, profiled composites, and composite/pre-pressed nonwoven systems. Profiling the composite plate by convexity/concavity has a positive effect on its sound absorption. It is also important to arrange the plate with the appropriate structure for the incident sound wave. For the composite layer with an added pre-pressed nonwoven layer, a greater increase in sound absorption occurs for the system when a rigid composite layer is located on the side of the incident sound wave. The addition of successive nonwoven layers not only increases the absorption but also extends the maximum absorption range from the highest frequencies towards the lower frequencies

Investigation of sound absorption properties of bark cloth nonwoven fabric and composites

The quest for sound-absorbing materials that are not only environmentally friendly, but also sustainable is the foremost reason for natural fibre-acoustic materials. Bark cloth is a natural non-woven fabric that is largely produced from Ficus trees. An exploratory investigation of bark cloth a non-woven material and its reinforcement in epoxy polymer composites has been fabricated and investigated for the sound absorption properties so as to find the most suitable applications and also to see whether bark cloth can be used in some applications in place of man-made fibres. Three types of material species were investigated with their respective composites. The fibre morphology showed bark cloth to be a porous fabric that showed promising sound absorption properties at higher frequencies. The sound absorption results of four-layer material selections of Ficus natalensis, Ficus brachypoda and Antiaris toxicaria bark cloth showed sound absorption coefficient of 0.7; 0.71 and 0.91 at f > 6400 Hz, respectively. The bark cloth reinforced laminar epoxy composites had reduced sound absorption coefficients, which ranged from 0.1 to 0.35, which was attributed to decreased porosity and vibration in the bark cloth fibre network

Conjugates of Chitosan and Calcium Alginate with Oligoproline and Oligohydroxyproline Derivatives for Potential Use in Regenerative Medicine

New materials that are as similar as possible in terms of structure and biology to the extracellular matrix (external environment) of cells are of great interest for regenerative medicine. Oligoproline and oligohydroxyproline derivatives (peptides 2–5) are potential mimetics of collagen fragments. Peptides 2–5 have been shown to be similar to the model collagen fragment (H-Gly-Hyp-Pro-Ala-Hyp-Pro-OH, 1) in terms of both their spatial structure and biological activity. In this study, peptides 2–5 were covalently bound to nonwovens based on chitosan and calcium alginate. Incorporation of the peptides was confirmed by Fourier transform -infrared (FT-IR) and zeta potential measurements. Biological studies (cell metabolic activity by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test and Live/Dead assay) proved that the obtained peptide-polysaccharide conjugates were not toxic to the endothelial cell line EA.hy 926. In many cases, the conjugates had a highly affirmative influence on cell proliferation. The results of this study show that conjugates of chitosan and calcium alginate with oligoproline and oligohydroxyproline derivatives have potential for use in regenerative medicine