Environmental concern has resulted in a renewed interest in bio-based materials. Among them, plant fibers are perceived as an environmentally friendly substitute to glass fibers for the reinforcement of composites, particularly in automotive engineering. Due to their wide availability, low cost, low density, high-specific mechanical properties, and eco-friendly image, they are increasingly being employed as reinforcements in polymer matrix composites. Indeed, their complex microstructure as a composite material makes plant fiber a really interesting and challenging subject to study. Research subjects about such fibers are abundant because there are always some issues to prevent their use at large scale (poor adhesion, variability, low thermal resistance, hydrophilic behavior). The choice of natural fibers rather than glass fibers as filler yields a change of the final properties of the composite. One of the most relevant differences between the two kinds of fiber is their response to humidity. Actually, glass fibers are considered as hydrophobic whereas plant fibers have a pronounced hydrophilic behavior. Composite materials are often submitted to variable climatic conditions during their lifetime, including unsteady hygroscopic conditions. However, in humid conditions, strong hydrophilic behavior of such reinforcing fibers leads to high level of moisture absorption in wet environments. This results in the structural modification of the fibers and an evolution of their mechanical properties together with the composites in which they are fitted in. Thereby, the understanding of these moisture absorption mechanisms as well as the influence of water on the final properties of these fibers and their composites is of great interest to get a better control of such new biomaterials. This is the topic of this review paper.

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The hygroscopic behavior of plant fibers: a review

Silicon nitride was firstly used as anticorrosive pigment in organic coatings. An effective strategy by combining inorganic fillers and organosilanes was used to enhance the dispersibility of silicon nitride in epoxy resin. The formed nanocomposites were applied to protect Q235 carbon steel from corrosion. The anticorrosive performance of modified silicon nitride with silane (KH-570) was investigated by electrochemical impedance spectroscopy (EIS), water absorption and pull-off adhesion methods. With the increase of immersion time, the corrosion resistance as well as adhesion strength of epoxy resin coating and unmodified silicon nitride coating decreased significantly. However, for the modified silicon nitride coating, the corrosion resistance and adhesion strength still maintained 5.7×1010 Ω cm2 and 7.6 MPa after 2400-h and 1200-h immersion, respectively. The excellent corrosion resistance performance could be attributed to the chemical interactions between KH-570 functional groups and silicon nitride powders, which mainly came from the easy formation of Si-O-Si bonds. Furthermore, the modified silicon nitride coating formed a strong barrier to corrosive electrolyte due to the hydrophobic of modified silicon nitride powder and increased bonds.

Excellent corrosion protection performance of epoxy composite coatings filled with silane functionalized silicon nitride

Moisture absorption–desorption effects in adhesive joints

https://hal.archives-ouvertes.fr/hal-01007227/document

Qualitative and quantitative assessment of water sorption in natural fibres using ATR-FTIR spectroscopy

Water transport in epoxy/MWCNT composites

Free/bound water absorption in an epoxy adhesive

Simple model to estimate adhesion of structural bonding during humid ageing

The wedge test is of considerable use for evaluating adhesion between two bonded rigid substrates. In its (usual) static form, release of elastic strain energy is equated to effective adhesion energy during crack growth. However, the test is usually treated as two-dimensional. In fact, it is really three-dimensional due to anticlastic bending effects of the bent beam(s) during crack propagation. We studied a composite material/epoxy/aluminium alloy system and observed a curved crack front during propagation. This leads to doubt as to the value of crack length to be inserted in the adhesion energy formula. In addition, by using the highly sensitive technique of speckle interferometry, it was possible to study anticlastic bending effects in a quantitative manner. Far from the crack front, agreement between theory and experimental is good, yet work remains to be done to understand the zone near the fracture zone.

/pdf/a-3d-effect-in-the-wedge-adhesion-test-application-of-4ov2w7o812.pdf

A 3d effect in the wedge adhesion test: application of speckle interferometry

A method of coating a field joint of a pipeline comprises: placing at least one body comprising a thermoplastics material around the field joint; heating the body in a mould cavity around the field joint to effect thermal expansion of the thermoplastics material; and constraining thermal expansion of the body in the mould cavity to apply elevated pressure between the body and pipe sections joined at the field joint. The elevated pressure improves bonding and fusing between the body, which forms a field joint coating, and the parent coatings and the exposed pipe sections of the pipe joints. The body need not be fully molten, which reduces the mould residence time including in-mould heating and cooling phases.

Techniques for coating pipeline field joints

A method of coating a field joint (34) of a pipeline comprises: placing at least one body (66) comprising a thermoplastics material around the field joint; heating the body (66) in a mould cavity (44) around the field joint (34) to effect thermal expansion of the thermoplastics material; and constraining thermal expansion of the body in the mould cavity to apply elevated pressure between the body and pipe sections joined at the field joint (34). The elevated pressure improves bonding and fusing between the body, which forms a field joint coating, and the parent coatings and the exposed pipe sections of the pipe joints. The body need not be fully molten, which reduces the mould residence time including in- mould heating and cooling phases.

Sylvain Popineau

Papers

Free/bound water absorption in an epoxy adhesive

Simple model to estimate adhesion of structural bonding during humid ageing

A 3d effect in the wedge adhesion test: application of speckle interferometry

Techniques for coating pipeline field joints

Method of and system for coating a field joint of a pipe