Polycarbonates-stabilisation

Comparatively little information is available concerning the use of additives in commercial grades of polycarbonate. Pigments, heat and ultraviolet stabilisers, blowing agents and fire retardants are used but the range of materials available... 

While additive analysis of polyamides is usually carried out by dissolution in HFIP and hydrolysis in 6N HC1, polyphthalamides (PPAs) are quite insoluble in many solvents and very resistant to hydrolysis. The highly thermally stable PPAs can be adequately hydrolysed by means of high pressure microwave acid digestion (at 140-180 °C) in 10 mL Teflon vessels. This procedure allows simultaneous analysis of polymer composition and additives [643]. Also the polymer, oligomer and additive composition of polycarbonates can be examined after hydrolysis. However, it is necessary to optimise the reaction conditions in order to avoid degradation of bisphenol A. In the procedures for the analysis of dialkyltin stabilisers in PVC, described by Udris [644], in some instances the methods can be put on a quantitative basis, e.g. the GC determination of alcohols produced by hydrolysis of ester groups. 

Mechanisms of degradation in condensation polymers, and the stabilisation of these polymers and non-polyolefin polymers such as poly(vinyl chloride) using organophosphites is discussed in terms of the stability of colour, thermal properties and molecular weight. Stabilisation of poly(ethylene terephthalate) and polycarbonate by organophosphites was studied experimentally. 5 refs. 

Two distinct mechanistic pathways have been proposed on the basis of the results obtained and they are shown in Schemes 13 and 14 for short and long wavelength irradiation conditions. All the products shown were identifiable. At high humidity the kinetics of the photooxidation of polycarbonate is influenced to some extent in that on short-wavelength irradiation only products which are soluble in water appear to be produced. Furthermore, the presence of the moisture has an accelerating effect on photodegradation of the polymer. The life expectancy of stabilised polycarbonate is expected to be at least... 

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... 

Some plastics additives, such as phthalates, bisphenol-A (BPA), and nonylphenols, present as plasticisers, can evaporate indoors and can be inhaled i.e., oestrogenic butyl benzyl phthalate is found in most vinyl floor tiles, adhesives, and synthetic leathers, and bisphenol-A is a breakdown product and plasticiser of polycarbonate (PC) mainly used as glazing material. In addition to plasticisers, there are also other additives used in plastics and rubbers i.e., stabilisers used in PVC window profiles and pipes are mostly lead-based, or they can be either barium/cadmium/zinc compounds. All of these can pose serious health hazards if they are above certain concentrations in the air, through evaporation from the system. Increase of temperature indoors speeds up this evaporation process. 

Later patents to General Electric Company [95, 96] claimed oxanilides which could be used to form polymeric stabilisers or could be added to the polymerisation stage of polycarbonates or polyesters to provide built-in stabilisers. An example of this type of structure IS HOPh-R-PhNH(C=0)(C=0)NHPh-R-PhOH. 

A wide variety of polymers can be foamed, including the polymethanes, polyisocyanurates, PVC, polystyrene, ABS, polycarbonate, PET, PBT, polyamides, PPO, EVA and the polyolefins. Other additives required for the foaming process besides blowing agents may include foam nucleating agents, stabilisers, surfactants, plasticisers, colourants, flame retardants and particulate fillers. 

Hostavin B-CAP from Clariant is a new UV stabiliser for polycarbonate and PET, based on a benzylidene-bis-malonate type UV absorber. It has good absorption in the high-energy range of the UV spectrum, and reduces yellowing. It does not interact with residual metal ions, and therefore does not affect either the colour or transparency of the polymer. Clariant recommends combining this UV absorber with other stabilisers for the long-term protection of polycarbonate and PET. 

Semi-volatile and non-volatile additives in polycarbonate (PC) and PC/polybutylene terephthalate blends have been determined without chromatographic separation using a particle beam interface for direct introduction of the samples into the mass spectrometer. Antioxidants, UV stabilisers, flame retardants, and slip agents were among the additives determined. The key to this approach was the speed and simplicity of identifying multiple additives in a single matrix [134]. 

By far the most important stabilisers are the hindered phenols, which are used in a wide range of polymers including the polyolefins, (e.g., PE and PP), polyamides, polycarbonate and PET. These stabilisers are effective both during processing at high temperature and for long-term use under ambient conditions. For increased effectiveness, they are usually combined with other stabilisers to attain an optimised combination of stabilisation and other properties such as discoloration. Often, the antioxidant is physically lost, primarily by extraction or volatilisation, rather than by chemical consumption [145]. The trend is therefore to use higher molecular mass antioxidants [132,139, 146]. 

The value of Gjc for PMMA is 500 J/m, that of a brittle thermoset is typically 100 J/m and G]c for polycarbonate is 1100 J/m. Note that, just because a material has a high value of K q, it does not follow that Gj is also high. Certain ceramics have high values of K,r but low values of Gjc. For example, partially stabilised zirconia has a of 6 MPa.m ... 

The most efficient way is to store the samples deep-frozen immediately after sampling, using polyethylene or polycarbonate containers. Under this condition, TBT was shown to be stable for 2-3 months. Polytetrafluoroethylene (PTFE) as the container material was shown to cause species loss, most probably owing to the porosity of this material. Polyfvinyl chloride) (PVC) bottles must be ruled out as container material, because PVC contains TBT for UV stabilisation which has been found to leach out of PVC containers and also from PVC tubes used for water supply. Several reviews on this topic can be found. ... 

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