Fracture toughness determination of adhesive and co-cured joints in natural fibre composites

Adhesive bonding has become more efficient in the last few decades due to the adhesives developments, granting higher strength and ductility. On the other hand, natural fibre composites have recently gained interest due to the low cost and density. It is therefore essential to predict the fracture behavior of joints between these materials, to assess the feasibility of joining or repairing with adhesives. In this work, the tensile fracture toughness (Gc n) of adhesive joints between natural fibre composites is studied, by bonding with a ductile adhesive and co-curing. Conventional methods to obtain Gc n are used for the co-cured specimens, while for the adhesive within the bonded joint, the J-integral is considered. For the J-integral calculation, an optical measurement method is developed for the evaluation of the crack tip opening and adherends rotation at the crack tip during the test, supported by a Matlab sub-routine for the automated extraction of these quantities. As output of this work, an optical method that allows an easier and quicker extraction of the parameters to obtain Gc n than the available methods is proposed (by the J-integral technique), and the fracture behaviour in tension of bonded and co-cured joints in jute-reinforced natural fibre composites is also provided for the subsequent strength prediction. Additionally, for the adhesively- bonded joints, the tensile cohesive law of the adhesive is derived by the direct method.

The mechanical properties of natural fibre reinforced cementitious composites

This thesis examined the mechanical properties of natural fibre reinforced cementitious composite materials. The results have provided essential data for the design of these composite materials for different applications. The theoretical model developed also allows accurate prediction of composite behaviour under different loading conditions.

Measuring the adhesion force on natural fibre surface using scanning probe microscopy

This work has focused on measuring the adhesion forces on both untreated and atmospheric helium plasma treated single jute fibre surfaces using scanning probe microscopy (SPM). The measurements were conducted on three differently aged surfaces for one week, three weeks and six weeks using a standard silicon nitride tip in force-volume (f-v) mode. Up to 256 adhesion data points were collected from various locations on the surface of the studied fibres using in-house developed software and the resulting data were statistically analysed by the histogram method. Results obtained from this analysis method were found to be very consistent with a small statistical variation. The work of adhesion, Wa, was calculated from measured adhesion force using the Johnson–Kendall–Roberts (JKR) and Derjaguin–Muller–Toporov (DMT) models. Increases in both adhesion force and work of adhesion were observed on jute fibre with certain levels of atmospheric plasma treatment and ageing time.

Prestressed natural fibre spun yarn reinforced polymer-matrix composites

Abstract We report that a prestressing technique similar to that traditionally used in prestressed concrete can improve the mechanical performance of flax fibre spun yarn reinforced polymer-matrix composites. Prestressing a low twist yarn not only introduces tension to the constituent fibres and compressive stress to the matrix similar as in prestressed concretes, but also causes changes to the yarn structure that lead to the rearrangement of fibres within the yarn. Prestressing increases the fibre packing density in yarn, causes fibre straightening, and reduces fibre obliquity in yarn (improved fibre alignment along yarn axis). All these changes contribute positively to the mechanical properties of the natural fibre yarn reinforced composites. Crown

State-of-the-art for extrusion and injection moulding FPC: natural Fibre Plastics Composites in Brazil

Environmental and economical concerns are stimulating research of new materials for construction, furniture, packaging and automotive industries. Particularly attractive are the new materials. This paper presents results about the properties of composites of polyhydroxybutyrate (PHB), polypropylene (PP) and High Density Polyethylene (HDPE) reinforced with natural fibres. The composites were prepared through the extrusion with natural fibres, in an ratio of 30% by weight. The quality of samples was tested utilising injection moulded samples, according to ASTM standards. Results showed that natural fibres can act as an excellent reinforcing material, resulting in low cost composites and improving economical and ecological interests.

Fibre coating composition

An abrasion-resistant, electrically conductive material comprising a natural fibre-containing substrate and an electrically conductive conjugated polymer coating thereon is disclosed. A process for preparing an abrasion-resistant, electrically conductive material is also disclosed. The process comprises providing at least one monomer capable of forming an electrically conductive conjugated polymer, and a suitable substrate having a substrate surface, subjecting the substrate surface to a surface treatment step to improve abrasion resistance, and exposing the substrate surface to a vapour of the monomer to form an electrically conductive conjugated polymer coating thereon.

Recent research on natural fibres and textiles

This paper provides an overview of recent research on a range of natural fibres and textiles. The focus is on work carried out at Deakin University’s Centre for Material and Fibre Innovation, which is a multidisciplinary research centre with over 100 researchers. The fibres include hemp, wool, silk, and alpaca fibres. Research on yarns, fabrics, and fine powders made from wool and silk fibres are briefly discussed also.

The within-fibre diameter variation of wool has been examined systematically, which highlights the importance of this hard-to-measure fibre attribute. A relationship between hemp fibre fineness and residual gum content has been established, which provides a rapid means of assessing the residual gum content in the degummed hemp fibres. Silk and wool fibres have been converted into ultrafine powders for advanced applications. The Resistance to Compression (RtC) behaviour of wool and alpaca fibres has been closely examined, which challenges the belief that RtC is a good indicator of fibre softness. Ways of reducing the hairiness of natural fibre yarns, predicting the pilling propensity of wool knits, and functionalising fabrics for superhydrophobicity and photochromic or colour changing effects are discussed.

The long-term performance of cementitious composites reinforced with coir fibre

Effective prediction of the long-term performance of natural fibre-reinforced cementitious materials is vital for their application. In this study, coir fibres of two different average lengths were combined with cementitious materials and chemical agents to form coir fibre-reinforced cementitious composites (CFRCCs). The composites long-term performance was assessed and compared with two different accelerated ageing processes, i.e. a cement-saturated water ageing, and alternate freeze-thaw ageing. The flexural properties were compared with the properties of the reference mortar. Overall, the flexural strength of 400 days naturally aged CFRCC specimens was weaker than that of the reference mortar. The toughness and ductility of the fibre-reinforced specimens, however, improved. The cement-saturated water ageing method gave a precise prediction of the flexural strength development of 400-day-old specimens, and the freeze-thaw ageing method worked very well for the toughness performance estimation of CFRCCs.

A simple and effective method to ameliorate the interfacial properties of cellulosic fibre based bio-composites using poly (ethylene glycol) based amphiphiles

In order to overcome interfacial incompatibility issues in natural fibre reinforced polymer bio-composites, surface modifications of the natural fibres using complex and environmentally unfriendly chemical methods is necessary. In this paper, we demonstrate that the interfacial properties of cellulose-based bio-composites can be tailored through surface adsorption of polyethylene glycol (PEG) based amphiphilic block copolymers using a greener alternative methodology. Mixtures of water or water/acetone were used to form amphiphilic emulsions or micro-crystal suspensions of PEG based amphiphilic block copolymers, and their deposition from solution onto the cellulosic substrate was carried out by simple dip-coating. The findings of this study evidence that, by tuning the amphiphilicity and the type of building blocks attached to the PEG unit, the flexural and dynamic thermo-mechanical properties of cellulose-based bio-composites comprised of either polylactide (PLA) or high density polyethylene (HDPE) as a matrix, can be remarkably enhanced. The trends, largely driven by interfacial effects, can be ascribed to the combined action of the hydrophilic and hydrophobic components of these amphiphiles. The nature of the interactions formed across the fibre-matrix interface is discussed. The collective outcome from this study provides a technological template to significantly improve the performance of cellulose-based bio-composite materials.