Additives heat stabilisers

Stabilisation with antioxidants may render PP unsuitable for food contact application as they may directly migrate into the food products, hydrolysing and imparting odour or taste to the food. Careful selection of a suitable stabiliser system is necessary for food contact applications. In addition, heat stabilisers could adversely affect the working of light stabilisers. 

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... 

Braun and Richter [923] have described an application of CE in additive analysis, namely quantitative analysis of heat stabilisers in PVC, such as Irgastab 17A and 18 MOK-N, which are metal-based (in the past usually Cd, Ba and Pb, now nontoxic Ca, Zn and Sn). Quantitative metal analysis is of interest for PVC recycling purposes. Various alternative approaches are possible for such quantitative analysis, such as XRF [924], polarog-raphy [925] and AAS [923], The performance of AAS, CE and complexometric titrations in the analysis of the heavy metal content in PVC was compared [923]. For all methods investigated the metals must be separated from the polymer and transferred into an aqueous phase. 

Intermaterial competition affects the additive business. For example, if metallocene polyolefins displace PVC markets, then the demand for heat stabilisers and plasticisers might decrease, while the need for products such as fluoropolymer processing aids, antiblocks and slip additives might increase. At present, PVC as the main user of additives is under threat as never before. However, green PVC, containing more environmentally friendly FRs and plasticisers as well as non-heavy-metal stabilisers, is now environmentally acceptable. 

These compounds are multifunctional additives. They can act as heat stabilisers, radical traps, decompose hydroperoxides, UV absorbers, etc. (iv) UV absorbers. This is the largest class of UV stabilisers. They work on the same principle as sun-screen lotions they contain chromophores that can absorb light in the 280-400 nm region and release the excess energy as heat and not high-energy radiation. They must be stable under processing conditions and should not react with the polymer nor decompose with UV radiation. 

Not all additives increase biological attack. Heat stabilisers for PVC fabrication, e.g., tin and lead organometallic compounds, promote fungal resistance. 

Additives used in the production of PVC are discussed with reference to the increasing pressure from environmental campaigners. In particular heat stabilisers and plasticisers are examined with data from the European Stabiliser Producers Association regarding market trends, materials substitution, and toxicity issues. 

Nonylphenol can be generated from some liquid heat stabilisers (in addition to many other possible sources) and it has been identified as persistent and oestrogenic (160). 

The main groups of additives have already been listed in Section 2. PVC formulation technology depends on the correct combination of several of these additives to suit the processing and end-use requirements. A basic rigid PVC-U formulation will contain medium to low molecular weight resin plus lubricant and heat stabiliser. Other additives will be included to improve processability and physical properties, give weathering resistance, improve cost performance, colour, etc. 

In a basic flexible PVC-P formulation, the resin usually has a medium to high molecular weight, with plasticiser and heat stabiliser essential. Other additives will be included for reasons of cost, electrical properties, etc. 

Heat stabilisers retard dehydrochlorination and autoxidation and reduce fragmentation. In addition, they also cure existing damage. 

Traditionally less effective as a heat stabiliser, much work has been carried out to develop more sophisticated and higher efficiency heat stabilisers based on Ca Zn. This is based on the concerns about barium as a heavy metal although there is no evidence of health or environmental concerns. In addition to further formulation development (454), complex polyphosphates (45), new Ca Zn intermediates (140) and new calcium technology (84) have all been promoted. 

Epoxidised soybean oil (ESBO) Epoxidised linseed oil (ELO) Primary use as a secondary heat stabiliser but also impart flexibility. Compatible only at relatively low addition levels. General use... 

There always has been an interest in additives that perform both a plasticising and heat stabilising effect. The most obvious of these is epoxidised soya bean oil (ESBO), or epoxidised esters, which can be incorporated at 2-6 phr (particularly with mixed metal heat stabilisers), to improve heat stability by HC1 absorption and also give a secondary plasticisation... 

Bromoacetone is only slightly soluble in water, but very soluble in alcohol, ether, acetone and other organic solvents. It is not very stable, even in the pure state. It polymerises in time, especially under the influence of light and heat, though this process may be impeded by the addition of stabilising substances. During the war a small quantity of magnesium oxide was added to bromoacetone and this checked the polymerisation for several months (Meyer). 

Stabilisers are intentional additives that help to retard the decomposition of plastics by heat, light (mainly UV), oxidation, and mechanical shear during processing and use. Antioxidants are required for almost all polymers, especially ABS, PE and PS. Heat stabilisers are required during the processing of PVC, because its molecules are very... 

PVC is one of the lowest-cost commodity resins, used extensively today due to its excellent chemical and mechanical properties. However, the thermal decomposition temperature of PVC is close to its processing temperature, and hence use of proper heat stabilisers during its processing is essential. In addition, PVC-wood composites (plastic lumber) discolour with time during outdoor use, and this can be improved by use of proper thermal stabilisers [16]. 

In addition to these basic heat stabilisers, there are others to consider ... 

In medical grade PVC, heat stabilisers (mainly varions calcinm-zinc formulations) are used for its processing, storage or autoclaving. Although barium-zinc additives are more effective as heat stabilisers for PVC, in several countries they are restricted for medical applications. 

PE has a very low compatibility with plasticisers and in fact it does not need plasticisers, however, they may contain other additives (i.e., UV and heat stabilisers). Chloroparaffins or brominated flame-retardants are common used in polyolefins. 

Most PVC stabilising systems are complex mixtures that contain a variety of additives which complement HCl removal. They include antioxidants to deal with the radicals formed in Scheme 3.5, sulfur compounds to remove hydroperoxides and olefin reactive agents to remove conjugated double bonds which are the source of colour and oxidative instability. Several functions may be found in the same molecule. Thus DOTGs are particularly powerful heat stabilisers for PVC and it has been found that the thiol produced by reaction with HCl has two additional antioxidant functions (Scheme 3.8). 

Further subjects in the spotlight are foaming agents, notably CFCs, which are now forbidden in many countries. Other additives or processing aids under debate, such as brominated and other halogenated flame retardants, cadmium and lead heat stabilisers and release agents which cause damage to the ozone layer, are discussed in more detail in Table 3.5 of Chapter 3. 

In addition to stabilising the fabric, the heat setting process will also result in an increase in the density of the structure through increased fibre consolidation. This in turn will further assist in achieving a higher level of filtration efficiency. 

Commonly used thermoplastics such as PE, polyvinyl chloride (PVC) and polypropylene (PP) are less costly than fluoropolymers, e.g. polyvinylidene fluoride (PVDF), but do not perform as weU in high temperature conditions. They also include plasticisers, heat stabilisers and fire retardants that can leach out. PVDF in its virgin form is highly pure and does not contain additives. 

Additive products have been improved, and several completely new products have been marketed. Individual polymers such as PVC and polypropylene have undergone changes in relative importance and market share. New health and safety eonsiderations and regulatory pressines have had major effects on the sales of eertain additives, espeeially heat stabilisers, brominated flame retardants and plastieisers. The trend towards reoyeling is afleeting additive selection. 

The additives business has been at the centre of environmental controversies for many years, and has made strenuous efforts to improve its products. Flame retardants for cable and wire insulation are increasingly made of nonhalogen, low-smoke materials, and there has been increased usage of phosphorus and metal hydroxide flame retardants in recent years. Major changes have also taken place in the heat stabiliser business, with lead compounds being voluntarily phased out over several years. 

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