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Molded Bakelite forms in a condensation reaction of phenol and formaldehyde, with wood flour or asbestos fiber as a filler, under high pressure and heat in a time frame of a few minutes of curing. The result is a hard plastic material. [27] Asbestos was gradually abandoned as filler because many countries banned the production of asbestos.
After cure, the PF prevents wood from springing back. This has been used to make high density, very hard wood products, known as “compreg” or “Staybwood”. [11] The increase in both strength and stability of the wood is due to the cross-linking of the resin components and the resin's ability to bulk the cell wall.
Typical engineered composite materials are made up of a binding agent forming the matrix and a filler material (particulates or fibres) giving substance, e.g.: Concrete, reinforced concrete and masonry with cement, lime or mortar (which is itself a composite material) as a binder; Composite wood such as glulam and plywood with wood glue as a binder
Diamond was the hardest known naturally occurring mineral when the scale was designed, and defines the top of the scale, arbitrarily set at 10. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, or the softest material that can scratch the given material.
Phenol-formaldehyde resins, as a group, are formed by a step-growth polymerization reaction that can be either acid- or base-catalysed.Since formaldehyde exists predominantly in solution as a dynamic equilibrium of methylene glycol oligomers, the concentration of the reactive form of formaldehyde depends on temperature and pH.
Cellulose acetate film, made from cellulose diacetate and later cellulose triacetate, was introduced in 1934 as a replacement for the cellulose nitrate film stock that had previously been standard. When exposed to heat or moisture, acids in the film base begin to deteriorate to an unusable state, releasing acetic acid with a characteristic ...
Wood-plastic composite. Wood–plastic composites (WPCs) are composite materials made of wood fiber/wood flour and thermoplastic(s) such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), or polylactic acid (PLA). In addition to wood fiber and plastic, WPCs can also contain other ligno-cellulosic and/or inorganic filler materials.
The hard transparent resins, such as the copals, dammars, mastic, and sandarac, are principally used for varnishes and adhesives, while the softer odoriferous oleo-resins (frankincense, elemi, turpentine, copaiba), and gum resins containing essential oils (ammoniacum, asafoetida, gamboge, myrrh, and scammony) are more used for therapeutic ...