Polyamides-stabilisation

Typical additive packages for engineering thermoplastics have been described by Titzschkau [9], such as processing aids for PA, PP, or PET/PBT, three-component additive packages for polyamides and polyesters (nucleating agent, lubricant and process heat stabiliser) and coated copper stabilisers for polyamides. Additive packages or combinations of up to five or more additives are quite common. A typical white window PVC profile formulation comprises an acrylic impact modifier, TiC>2, CaCC>3, calcium stearate, a... 

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. 

Figure 12.3 Examples of the weathering performance of (a) a stabilised HDPE nonwoven and (b) a polyamide/polyester nonwoven deliberately unstabilised against ultraviolet radiation. Both were exposed to artificial weathering using three different types of apparatus and to natural weathering in two locations. All results are plotted against radiant exposure (total ultraviolet light energy...

To see if oxidative spreading could take place between different polymers, initiation of stabilised PP using a piece of unstabilised polyamide 6 (PA 6) was performed [79]. However, PA 6 can not initiate oxidation in PP even if oxidising PA 6 is placed in direct contact with PP. To clarify the processes of cross spreading between different polymers more experimental work is necessary. 

There is interest in trace metal levels in both natural and synthetic fibres and fabrics but perhaps most interest is in synthetic fibres as these may contain residues of catalysts, treatments or stabilising agents. Reviews have been published of trace-metal analysis of rayon, polyamide, polyester and polypropylene fibres [178] and of cotton fabrics, especially for flame... 

For polyamide/wool blended fabrics fluorescent brightening agents (1 -2%) are applied following hydrogen peroxide bleaching in presence of stabiliser (3-5 g/1). The treatment is carried out at 70-75 C for 45-60 min and then rinsed and dried. 

A polyamide which sequence specfically recognises the minor groove of DNA has been demonstrated to bind simultaneously with the third strand of a triplex in the major groove of DNA although no co-operativity of binding was observed. The stabilisation of triple helices by oligopeptides has been studied. Pentalysine was the most effective at triplex stabilisation. 

Figure 7,14 A forecast of the growth of heat stabilised glass fibre-reinforced polyamide 66 present in end-of-life vehicles (elv).

Celanese Corporation [85] claimed it was possible to heat stabilise filled PTT or PBT with low levels (0.25-1 wt%) of a polyamide such as Nylon 6, Nylon 6,6 or Nylon 6,10. 

Tetraalkyl- and 1,2,2,6,6-pentaalkyl piperidine-based HALS which have been claimed specifically as stabilisers for aromatic polyesters include alkylamine derivatives such as pentakis(2,2,6,6-tetramethyl-4-piperidinyl)diethylenetriamine-N,N,Nl N", N -pentaacetate [184] unsymmetrical siloxanes with HALS moieties at one end and a reactive group on the other, e.g., -Si(CH2)30H group capable of reacting with acid chain ends in the polymer [185] and HALS diepoxides, which chain-extend and UV-stabilise polyesters and polyamides [186]. 

A HALS-based additive system has been developed by Clariant based on salt-like reaction products of HALS with phosphorus-containing organic acids [199] or carboxylic acids [200]. Despite their salt-like character, these additives are said to stabilise in the normal HALS manner, and additionally provide improved processing, mechanical properties and appearance. They are specifically aimed at polyesters and polyamides. An example of one of these compounds is the... 

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. 

As implied above, fluoropolymer processing aids can interact with HALS and reduce their effectiveness. The reaction with HALS and also with polyurethanes and polyamides is thought to involve the vinylidene fluoride comonomer units of the fluoropolymer, resulting in poorer performance and discoloration. Grades of fluoropolymer that do not interact with hindered amine light stabilisers have now been developed. 

The protection of polyamides against light has been an important objective. Clariant markets a sterically hindered amine, Nylostab S-EED, as a UV stabiliser and antioxidant for polyamides. 

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 two products are reported to be easily dispersed, have good rheological properties and can be easily coloured. They can be used in injection moulding processes, but die manufacture of complex shapes often requires high temperatures and high injection speeds. Exolit OP 1312 is a specially-stabilised system for polyamide 66 and its main applications are in flame retarded injection mouldings for the electrical and electronic industries. 

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