Stabilisers polyurethane

Figure 224 Scheme for an aqueous, anionically stabilised polyurethane dispersion. Source Klein H.P. and Schwab, M., Aqueous polyurethane dispersions - an environment friendly alternative for high quality paint systems, Resin News, number 29 (July) published by Hoechst AG, Frankfurt, 1993... 

It is a well-known fact that specific plastic materials like flexible PVC, Polyurethane or Silicone may be easily attacked by microorganisms leading to discoloration or mechanical failures.14 This susceptibility to microbial attack is mainly attributed to the plasticiser content of the material as well as other ingredients such as stabiliser or antioxidants.5,6 The predominant organisms on the surface of those plastics are fungi and actinomycetes and it is said that by the action of their extracellular enzymes other organisms such as bacteria may be able to grow on the material.7... 

Kim el al. [582] have described maleimide-based antioxidants melt grafted onto low-MW PE. IR spectroscopic methods and titration were used for the quantitative determination of the extent of grafting of the monomeric antioxidant. Smedberg el al. [583] have characterised polymer-bound stabilisers by FTIR and NMR. The binding of antioxidants and photostabilisers to polyurethanes was verified by tJV/VIS spectroscopy [584]. 

In a polyurethane elastomer analysed by isobutane CI-MS and CI-MS/MS in TD/Py-CIMS (TD, 20-200°C Py, 200-300 °C) mode MDI (diisocyanate), BDO (chain extender), Stabaxol P (stabiliser), AA/ BDO/HDO (cyclic adipate) and residual cyclic ester oligomers were identified [65]. 

Surfactants used as lubricants are added to polymer resins to improve the flow characteristics of the plastic during processing they also stabilise the cells of polyurethane foams during the foaming process. Surfactants are either nonionic (e.g. fatty amides and alcohols), cationic, anionic (dominating class e.g. alkylbenzene sulfonates), zwitterionic, hetero-element or polymeric (e.g. EO-PO block copolymers). Fluorinated anionic surfactants or super surfactants enable a variety of surfaces normally regarded as difficult to wet. These include PE and PP any product required to wet the surface of these polymers will benefit from inclusion of fluorosurfactants. Surfactants are frequently multicomponent formulations, based on petro- or oleochemicals. 

Industrially, silicone surfactants are used in a variety of processes including foam, textile, concrete and thermoplastic production, and applications include use as foam stabilisers, defoamers, emulsifiers, dispersants, wetters, adhesives, lubricants and release agents [1]. The ability of silicone surfactants to also function in organic media creates a unique niche for their use, such as in polyurethane foam manufacture and as additives to paints and oil-based formulations, whilst the ability to lower surface tension in aqueous solutions provides useful superwetting properties. The low biological risk associated with these compounds has also led to their use in cosmetics and personal care products [2]. 

Oligoorganosiloxanes with alkoxyoxyalkylene fragments in their branches have recently been widely used as surface active agents, which regulate foam forming and foam stabilising in the production of various foamed polyurethanes. 

Oligomer I is used as a regulator and stabiliser in the production of elastic polyurethanes based on polyethers, rigid and semirigid polyurethanes oligomer II is used in the production of elastic polyurethanes based on esters. 

The dielectric strength of polyethylene has been measured as a function of additive concentration while in stabilised polymers the depth of degradation was found to be uniform . HALS have been found to be effective stabilisers for UV cured coatings and do not influence the cure rate . Bleached wood pulps can be effectively stabilised by ascorbic acid and wool by hydroxy-benzotriazoles and HALS . Hydroxybenzotriazole stabilisers also protect wood pulp and polyurethanes by co-reaction . The spectroscopic properties of monomeric and polymeric benzotriazoles have also been compared . UV absorbers are effective in clear coats and when grafted to wood . Dihydroxybenzophenone stabilisers inhibit the chain scission in the photodegradation of poly(methoxyacrylophenone) while tin stabilisers have also been found to photostabilise PVC . 

A survey of plastics-containing objects in the British Museum and the National Museum of Denmark showed that 1% of objects were actively deteriorating and were in immediate need of conservation, while 12% exhibited deterioration and required cleaning, stabilising and repair. All the acute objects contained cellulose nitrate, cellulose acetate, plasticised PVC or polyurethane foam. Most objects (60%) were defined as being of low conservation priority, that is, they were in a stable condition but needed some treatment such as cleaning. Only just over one quarter required no conservation treatment. In general, deterioration of plastic objects in museums is visible within 5-25 years of collection. 

It has been mentioned above that foams can unfavourably affect the refining processes. Formation processes of non-aqueous foams are not well enough studied. In a vast review [264], comparison between aqueous and non-aqueous foams has been made. The stabilisation of non-aqueous foams (e.g. on a hydrocarbon basis) seems to be impossible with usual hydrocarbon surfactants because of the weak liquid-gas interfacial tension lowering gradients. Fluorinated or silicone-type surfactants can be used as eventually better stabilisers. These recommendations are, in our opinion, only applicable to the production of the so-called hardening foams (polystyrene foams, polyurethane foams etc.). 

G Capocci, Advances in the light stabilisation of polyurethanes , 30th Annual Polyurethane Tech/Marketing Conference, 1986, pp 220-227. 

Dimensional Stabilising Additives for Flexible Polyurethane Foams... 

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