Natural Polymers and Cellulose Esters

9 Natural Polymers and Cellulose Esters The photodegradation of painted wood panels has been found to fail at the wood paint interface 4 while acid treatment of methylcellulose accentuates its rate of photodegradation . Silk fibres have been found to form a roll-like structure after laser ablation with 193 nm light whereas the weatherability of lacquer coated leather has been investigated in a number of weatherometers . Poly(acrylic acid) up to 25% w/w has been found 

The photostabilisation of polymers still maintains a high level of activity with the mechanistic action and performance of hindered piperidine compounds continuing to attract interest. Some interesting reviews have appeared with one very extensive and highly recommended paper on the mode of action of hindered piperidine light stabilisers while another has dealt with their manufacturing properties. The kinetic reactions and photophysics of light stabilisers have been covered in another review as has the stabilisation of polyacetals.  

A hindered amine light stabiliser has been found to enhance the light stability of blends of low and linear low density polyethylene with the latter contributing linearly to the overall stability of the blend. In coatings hindered piperidine light stabilisers are also effective especially when used in conjunction with a benzotriazole absorber while surface protection of styrene copolymers with 2-(2-hydroxy-5-vinylphenyl)benzotriazole requires a small amount of a hindered piperidine stabiliser. Polymeric hindered piperidine compounds on the other hand have been found to inhibit the singlet oxygen attack on poly(butadiene).  

Some interest continues in absorber systems. Silane and styrene monomers have been copolymerised with 2-vinylphenyl benzotriazole stabilisers in order to graft the stabilisers into the polymer chain °. When doped into plastics materials they were found to exhibit high surface activity. However, there is a conflicting report from other workers on similar structures where it is claimed that such polymeric stabilisers do not photoprotect the surface of polystyrene . Poly(2,6-dimethyl-l,4-phenylene oxide) has been effectively stabilised with an ortho-hydroxyphenyl benzotriazole stabiliser while in another study these compounds are claimed to be lost rapidly from polycarbonates . Other types 

These compounds have been found to be more effective than the tin alkylmaleates. Here stabilisation efficiency has been found to depend upon the nature of the substituents on the aryl rings of the molecule and highly effective synergism is observed with phenyl salicylate. Initially, the chlorine radicals from the photooxidation of the polymer are believed to react with the stabiliser according to scheme 13. The stabiliser radicals will then react with the polymer chains and graft in as shown. The 

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