Hardening, glue

Skin irritation can also be caused by amine accelerators, e.g., MDA (van Joost et al. 1987), triethylene-diamine (Adams 1983) and triethylamine (Malten 1964). Concentrated liquids may even be corrosive. The irritant effect of diisocyanates in the hardeners, glues and paints may also be attributed to the solvents used in these products. Completely hardened PU products usually do not cause skin problems. However, some unreacted isocyanate monomer may remain in surplus inside the PU foam, even after curing. During machining and cutting, PU dust containing isocyanate is produced. When heated to above 250 °C, PU polymers decompose into isocyanates and nitrogen oxides, and may then cause dermatitis (Bjorkner 1992). 

Correlations Between the Composition of Melamine Resins and Properties of Hardened Glue Lines and Wood-Based Panels... 

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). 

The penetration behavior of resins into the wood surface also is influenced by various parameters, like wood species, amount of glue spread, press temperature and pressure and hardening time. The temperature of the wood surface and of the glue line and hence the viscosity of the resin (which itself also depends on the already reached degree of hardening) influence the penetration behavior of the resin [79]. 

Acid-induced gelling reactions of PF resins can cause severe deterioration of the wood substrate and therefore have lost any importance in the wood adhesives field. Pizzi et al. [85] describe a procedure for the neutralization of acid-hardened PF glue lines by partly using as hardener a mix of p-toluene sulfonic acid with a... 

The addition of urea to a phenolic resin causes several effects (1) decrease of the content of free formaldehyde (2) decrease of the viscosity of the glue resin (3) acceleration of the hardening reaction via the higher possible degree of condensation of the resin at the same viscosity (4) reduction of the costs of the resin. 

Polyurethane adhesives are formed by the reaction of various types of isoeyanates with polyols. The polar urethane group enables adhesion to various surfaees. Depending on the raw materials, glue lines with rubber-like elastic to brittle-hard behavior ean be aehieved. The presence of reactive terminal groups provides a ehemieally hardened adhesive. When polymerized to a high enough molecular weight, the adhesive ean be physically rather than chemically hardened, i.e. a hot melt. 

Because of the reasons described above, the core layer and face layers are glued separately, that is, the core layer contains rather coarse particles, but the face layers contains rather fine particles. However, the two distributions might overlap to some extent. This separate gluing enables one to use different compositions of the glue resin mixes (e.g. different addition of water and hardener) and different gluing factors for the individual layers. 

Volatile acid hardeners such as hydrochloric acid and formaldehyde (which oxidises to formic acid) present in glues in plywood contribute to vapour corrosion, as can varnishes and paints. ... 

Formalin is an aqueous solution of approximately 40% formaldehyde. It was traditionally used to preserve biologic specimens, but its identification as a mild carcinogen has curtailed its use as a preservative. Formaldehyde is widely used to produce synthetic resins. Resins are sticky, liquid organic compounds that are insoluble in water. They often harden when exposed to air. Many commercial types of glue are resins. Natural resins are produced by plants as a response to damage. When a plant suffers external damage, natural resins flow to the area and harden to protect the underlying... 

A safety match requires for its ignition a rubbing on a "striking strip" which is covered with mixture such as consisting of red phosphorus 53, Sb sulfide 42 charcoal 5% in a binder such as NC lacquer, animal glue, dextrin, casein, plus hardener. Sb sulfide and charcoal serve as extenders to the phosphorus. 

Animal glue. mixed with casein and hardener as given in USP 2722484(1955) by I. Kowarsky... 

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