Liquid resins

In recent years, production of liquid resins of higher purity, ie, higher monomer content and fewer side-reactions, has been accompHshed. This is in response to more stringent product quality requirements. 

Liquid resins containing bromine (ca 49 wt %) can also be prepared directly from tetrabromobisphenol A and epichlorohydrin and are used for critical appHcations where a high degree of flame retardancy is required. 

The term epoxy is familiar to nonchemists because of the widespread use of epoxy glues and resins. These are crosslinked polyether thermoplastics made from a liquid resin which is typically a mixture of bisphenol A diglycidyl ether (70) and a polymer (71 Scheme 86). The liquid resin is cured or hardened to the final resin by mixing with a crosslinking reagent, which can be an acid, a di- or poly-alcohol, or a di- or poly-amine (Scheme 86). 

After deactivation and removal of the initiating system, the eoumarone-indene resin is separated from solvent and low moleeular weight materials by vacuum distillation. The removal of the low moleeular weight materials is important beeause they produce strong odour, they aet as softeners and they eause an undesirable deerease in softening point. Therefore, at this stage the softening point of the eoumarone-indene resins is adjusted. Finally, stabilizers are added to the liquid resin while it is still hot to inhibit further oxidation (whieh eauses diseolouration and odour). 

Polybutene resins. These liquid resins are obtained by cationic polymerization of petroleum C4 streams in the presence of AICI3 at relatively low temperature. Temperature and AICI3 concentration are important factors as they influence the molecular weight and viscosity of the final resin. After reaction, the mixture is deactivated with water, methanol, ammonia or aqueous sodium hydroxide. The organic layer is separated and distilled to remove solvent and unconverted material. 

Density. Density is the mass of unit volume at a given temperature. For solid resins, density is evaluated according to DIN 51 757 at 20°C, whereas for liquid resins DIN 1995 U2 at 20°C is more appropriate. Densities of resins usually are in the range 0.88 to 1.15 g/cm. ... 

Perhaps the lowest cost accelerators for PF resoles are inorganic carbonates and carbon dioxide [118,183,184], Potash and soda ash have been added to PF plywood mixes for many years. Though the results are not as dramatic as those seen with organic esters, resorcinol, and related derivatives, they work well and are cost effective. The mechanism by which they operate is not known. Levels between 0.25 and 2%, based on liquid resin are normally used. 

The higher the content of melamine, the higher is the stability of the hardened resin against the influence of humidity and water (hydrolysis resistance) [17, 45,46]. Resins containing melamine can be characterized by the molar ratio F (NH2)i or by the triple molar ratio F U M. The mass portion of melamine in the resin can be described as being based on the liquid resin or based on the total mass of urea and melamine in the resin (Table 6). MUF-resin hardener addition usually is distinctly higher than in UF-resins. 

Usually alkaline NaOH is used as catalyst, in an amount up to one mole per mole phenol (molar ratio NaOH/P), which corresponds to approx. 10 mass% alkali in the liquid resin. The pH of a phenolic resin is in the range of 10-13. The biggest part of the alkali is free NaOH, a smaller part is present as sodium phenate. The alkali is necessary to keep the resin water-soluble via the... 

The same chemical mechanisms and driving forces presented for phenol-formaldehyde resins apply to resorcinol resins. Resorcinol reacts readily with formaldehyde to produce resins (Fig. 2) which harden at ambient temperatures if formaldehyde is added. The initial condensation reaction, in which A-stage liquid resins are formed, leads to the formation of linear condensates only when the resorcinol/formaldehyde molar ratio is approximately 1 1 [119]. This reflects the reactivity of the two main reactive sites (positions 4 and 6) of resorcinol [120]. However, reaction with the remaining reactive but sterically hindered site (2-positiori) between the hydroxyl functions also occurs [119]. In relation to the weights of resorcinol-formaldehyde condensates which are isolated and on a molar basis, the proportion of 4- plus 6-linkages relative to 2-linkages is 10.5 1. However, it must be noted that the first-mentioned pair represents two condensa-... 

Structural carbon shapes fabricated by heating coke with a mixture of tar and pitches are porous and are made impermeable by impregnation with a resin (usually a phenolic resin). Cashew nut shell liquid resin is used when resistance to alkalis and acids is required. 

Liquid resins are usually reinforced with fibers (glass, asbestos), because of their brittleness. They are almost always used for process plant construction. As liquid resins they can be catalyzed to cure at room temperature and low pressures. Relatively cheap wooden molds are required to build quite large items such as tanks and ducting on a one-off basis. The principal materials in this group of plastics are described below. 

Process in whicli continuous strands of roving or roving tape are wound, at a specified pitch and tension, onto the outside surface of a mandrel. Roving is saturated with liquid resin or is preimpregnated with partially cured resin. Application of heat may be required to promote polymerization. 

In another method, the liquid resin is sprayed onto wood chips. The condition for rapid and complete impregnation of the wood chips or sawdust in resins is to dilute the resins either in monomer [40] or in swelling agents [41]. Dilution of the resin with monomers of roughly 10% permits complete impregnation within a very short period. The mixed or impregnated product was subjected to press under pressure and temperature to produce a board with a natural appearance. Percent-... 

Liquid resin-based systems which, like the chemical surface hardeners, penetrate into the surface of a concrete topping or directly finished slab and protect the acid-susceptible cement matrix from attack and, at the same time, strengthen the surface of the concrete are now being increasingly used. These in-surface seals leave the slip resistance of the concrete floor virtually unchanged but the treated floors are easier to clean and are more durable. 

Two-pack epoxies These were first patented in 1938 but were not in general production until 1947. They have been very widely used over the last decade. Produced from the by-products of the petroleum industry, the basic epoxy resins may be in the form of relatively low-viscosity liquid resins or they may be solid resins of increasing hardness. Both solid and liquid resins can then be reacted with a number of different curing agents. This means that almost any type of film and with any required properties can be made. 

Thermosetting epoxy and polyurethane chemically-cured liquid resins can provide, among other characteristics, superior abrasion resistance coatings. Solvent-free formulation applied by hot spray techniques can achieve film thicknesses of up to 5 mm. 

Resin cements or polymer cements have been reviewed by Chandra, Justnes, and Ohama [343]. Polymer cements are materials made by replacing the cement at least partly with polymers. Cements can be modified by latex, dispersions, polymer powders, water-soluble polymers, liquid resins, and monomers. 

Increase viscosity, e.g. magnesium oxide in unsaturated polyester resins increases the viscosity so much that a liquid resin becomes a tackfree solid, suitable for making sheet moulding compound (SMC). A relatively high viscosity is also desirable for latex compounds used to coat textiles. 

UV-radiation curing has become a well-accepted technology which has found numerous industrial applications because of its distinct advantages 1-3. One of its main characteristics is the rapidity of the process which transforms quasi-instantly the liquid resin into a solid polymer under intense illumination by a UV-source or a laser beam4. The polymerization rate can be finely controlled by acting on the initiation rate through the intensity of the UV radiation. It is... 

Liquid propellants, 10 726 Liquid propylene, compressed, 20 770 Liquid pyridine, 21 93 Liquid range, of ionic liquids, 26 848-851 Liquid resins, viscosities of, 10 385 Liquid-resist interface, 15 187 Liquid resole resins, in air and oil filters, 18 790... 

Depending on their ultimate form and uses, polymers can be classified into plastics, elastomers, fibres or liquid resins. These are defined as follows ... 

The pigments are incorporated into the resins before crosslinking to ensure homogeneous coloration. This can be done in the molten resin, for example in a kneader at about 90°C, or in dissolved or liquid resins by the liquid resin method. Ball mills are normally used for coloring prewetted powder molding compounds that have not yet been cured. 

By far the most common form of reinforcement is fiberglass. Products using unsaturated polyester resin as a matrix and fiberglass fiber reinforcements are commonly referred to as composites , laminates or FRPs (fiber-reinforced plastics). The latter reinforcements are sold as continuous roving, which is continuously chopped in place with a liquid resin stream, chopped roving mat, woven... 

Simple liquid resin casting in an open or closed mould o is suited for small and medium output... 

Table 2.17 analyses some examples of the relative processing cost versus the annual production in units. The various technologies listed are not suitable for all materials or parts machining is used with numerous materials rotational moulding uses liquid resins vacuum forming uses thermoplastic sheets blow moulding uses special grades of thermoplastics... 

Syntactic foams are obtained by mixing hollow micro- or macro-balloons, generally made of glass but sometimes of polymer, directly with a liquid resin, generally a thermoset. Some extend this definition to all composites with a foamed core. 

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