Hardener, resin

Reaction of one mole of acetaldehyde and excess phenol in the presence of a mineral acid catalyst gives l,l-bis(p-hydroxyphenyl)ethane [2081-08-5], acid catalysts, acetaldehyde, and three moles or less of phenol yield soluble resins. Hardenable resins are difficult to produce by alkaline condensation of acetaldehyde and phenol because the acetaldehyde tends to undergo aldol condensation and self-resinification (see Phenolic resins). 

It is thus seen that as a class the primarily aliphatic amines provide fast-curing hardeners for use at room temperatures. With certain exceptions they are skin sensitisers. The chemical resistance of the hardened resins varies according to the hardener used but in the case of the unmodified amines is quite good. The hardened resins have quite low heat distortion temperatures and except with diethylenetriamine seldom exceed 100°C. The number of variations in the properties obtainable may be increased by using blends of hardeners. 

The deterioration of a bond line can occur due to (1) the failure of the resin (low hydrolysis resistance, degradation of the hardened resin causing loss of bonding strength) (2) the failure of the interface between resin and wood surface (replacement of secondary forces between resin and reactive wood surface sites by water or other non-resin chemicals) (3) the breaking of bonds due to mechanical forces and stresses (the influence of water will cause swelling and therefore movement of the structural components of the wood-based panels). 

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. 

Depending on the formulations various grades of water resistance can be achieved according to EN 204 (D1-D4) [172], For the two-component PVAc adhesives crosslinking and hence a duroplastic behavior is effectuated by addition of hardening resins (e.g. on basis of formaldehyde), complex forming salts (based... 

Nitrocellulose alone will not give a continuous coating. It must, therefore, be blended with other components comprising a plasticiser and a hardening resin. An extensive range of such products is available, the ultimate choice depending on the properties required. 

Propylene oxide was introduced into a container that contained epoxy resins it detonated. This accident was put down to compound polymerisation catalysed by triamines or superior homologues, which are used to harden resins (for example, triethylenetetramine). 

Ester-cured alkaline phenolic system. The resin is an alkaline phenolic resin (essentially the same as the self-hardening resins of this type). Sand is mixed with the resin and blown or manually packed into a core box. A vaporized ester, methyl formate, is passed through the sand, hardening the binder. The total resin and peroxide addition is 1.5%. Compression strengths of 5000 kPa (700 psi) are possible. 

Acid generation in photoresist films add photogeneration vs. dose, 3233/ acid present after irradiation, 32,34r add present before irradiation, 32 quantum yield, 3234 Acid hardening resin resists cross-linking adivation energy determination, 87,89 cross-linking chemistry, 87 determination of acid generated, 87-88 effect of postexposure bake temperature and time, 87... 

A three-dimensional network formed in the presence of the dispersed filler and therefore the process proceeded in the thin surface layer on the surface of the previously hardened resin (filler). The use of such a system enables the physical structure of the polymer to be changed without changing its chemical nature. At the same time, all the effects usually observed for filled polymers may be expected to be present. 

From experimental data on viscoelastic properties the fractional free-volume was calculated according to the WLF equation for pure hardened resin, filled with different amounts of polymeric filler obtained from the same hardened resin. By using special methods for preparation of filled specimens, it was possible to obtain... 

Similar to the resinates are the so-called Hardened resins, consisting of colophony and small amounts of lime or zinc oxide. 

Effect of Hardener/Resin Composition on Degree of Cure. 

As to hardening resin of FRP reinforcement, althogh the compatibility with fire-resistance should be taken in to account, in order to make FRP reinforcement more recyclable, conversion from thermosetting resin into thermochemically, photochemically and biochemically resolvable resin is recommended. 

To obtain sap, a plant must be wounded by piercing the stem or by peeling off a thin layer of the bark. Most tree saps thicken and harden when exposed to the air, but some trees produce liquid resins. Air-hardened resins can be stored indefinitely in air-tight containers. 

Formaldehyde also undergoes addition, condensation, and polymerization reactions. The most interesting addition reaction of formaldehyde is the addition of ammonia. In this reaction hexamethylene tetramine (urotropine) is formed. This is used in medicine to clean urethras, in industry to harden resins and is also added to foodstuffs as a preservative. 

Place embedded tissue sample on glass microscope slide coated with liquid release agent. Place a drop of liquid TAAB resin onto one flat end of a hardened resin stub. Place same end of stub on top of tissne sample. Place a small drop of resin on the other end of the stub and affix a small piece of paper with a label identifying the sample. A circnlar piece of paper resnlting from using a hole puncher will suffice. 

BS 6319 Part 5 1984 Method for determination of density of hardened resin compositions... 

Further proof of complex reactions between propylene carbonate and phenolic nuclei leading to compounds in which the carbonic acid has attacked the phenolic ring has been presented [23] based on the NMR spectrum of the product of the reaction of resorcinol with propylene carbonate, in the absence of formaldehyde. Resorcinol was chosen as its aromatic ring is a stronger nucleophile than that of phenol and thus if any reaction had occurred this would be less elusive and much more easily observed [23]. The reaction products which appeared to be formed were carboxylic and dicarboxylic species. That they might be present was also derived by NMR [23]. It must be pointed out that such structures need to be only transitory and not permanent to obtain the same effects noted experimentally. Such a subsequent lability could be the reason why it is difficult to observe such linkages in the hardened resin except for faster reacting phenols where they can be observed due to early immobilization of the network which surely occurs. 

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