Lubricant, internal plasticiser

Lubricants can be classified as internal or external lubricants. Internal lubricants should be partially miscible with the polymer at processing temperatures (i.e., behave similar to a plasticiser), but phase separate at ordinary temperatures. Whereas plasticisers are completely miscible with the bulk polymer, lubricants have a limited solubility. 

Lubricants have been classified as either internal or external. Typically, internal lubricants have meant materials that are compatible with PVC that promote flow. The difference between internal lubricants and plasticiser is that the internal lubricant is only soluble at high temperature whereas the plasticiser is soluble and functional at room temperature. External lubricants on the other hand, are said to be incompatible and come to the surface and create metal release. It is reported that there are two distinct types of external lubricants. Internal lubricant efficiency can be readily predicted by simple mathematical formula and that partial substitution of esters for paraffin allows the reduction of modifier or increased filler levels to achieve savings without loss of any physical properties. 

In extrusion - blow moulding operations, molten polymer passes through a stage where it is processed with little external support. In these circumstances the moulding is likely to distort. The incorporation of a melt strength additive reduces the possibility of this occuring. Frequently, the materials used to improve melt strength are the same as those used for internal lubrication or plasticisation. 

It has been seen that internal lubricants are essentially low molecular weight flow promoters which, unlike plasticisers, have little effect on the... 

Plasticisers are added to PVC to achieve flexibility and workability. The flexibility or softness is determined by the type of plasticiser and level used in relation to the PVC (phr). They also operate as an internal lubricant between the PVC molecules. Based on organic esters, e.g., phthalates, adipates, trimellitates, phosphates, etc., addition levels can be as low as 20 phr for semi-rigid to 100 phr for very flexible applications. The effect on the thermal stability significantly depends on the physical state of the PVC-plasticiser system (260). The relative amount of crystalline PVC in PVC/diethylhexyl phthalate has been identified on the basis of a combination of carbon-13 solution and solid state nuclear magnetic resonance (NMR) (361). 

In PVC-P applications, the plasticiser acts as an internal lubricant and external lubricants can be added to increase output etc. Excessive levels or incorrect choice can cause problems with post treatment, e.g., printing or blooming on ageing. 

Lubricants may therefore act as either as an external or an internal agent. Depending on their chemical nature, a few may have secondary actions such as dispersing agents, plasticisation, or slip agents. These are usually included up to a 1% level. 

Additives are used for a wide variety of purposes, and may be classified as fillers, anti-oxidants, stabilisers, plasticisers, fire retardants, pigments and lubricants. Anti-oxidants and stabilisers are usually used in rather small quantities in order to prevent degradation of the polymer when it is exposed to air, light and heat the intention here is to maintain the properties of the polymer rather than to modify them. Fillers may be used either simply to produce a cheaper product or to improve the properties, in particular the mechanical properties. Lubricants may be used externally, to prevent adhesion of the polymer to the processing equipment, or internally, either to aid flow during processing or to reduce friction between the product and other materials. 

A plasticiser is a small-molecule additive deliberately introduced into a polymer in order to act as a sort of internal lubricant to reduce Tg. A very familiar example is the use of plasticisers to make PVC flexible at room... 

DSC has been used in the determination of an internal moulding lubricant (low-MW PE) in a polyphenylene oxide (PPQ) based resin, where the area under the melting peak is proportional to the amount of PE [82]. De et al. [83] have used thermal analysis methods (DSC, TG) for characterisation of polyurethane-mica composites DSC of TPU-mica was carried out to determine the Tg of composites. Examination of Tg by DSC reveals the plasticising effect of small molecules on the glass transition behaviour of polymers. The addition of plasticisers lowers Tg of NBR [84]. The plasticiser content in... 

Plasticiser efficiency in PVC can be evaluated by a number of semi-empirical tests, such as lowering of Tg as the level of plasticiser is raised. Addition of 20% DOP decreases Tg of PVC from 85°C to 30°C. On a routine basis, a moulder can check incoming materials by monitoring Tg [82]. DSC has also been used to determine the effectiveness of various lubricant additives for PVC [95]. Depending on the processing period, and therefore the temperature profile, each lubricant underwent a change in the internal V5-. external nature of its behaviour. Monitoring of Tg produced evidence for the effectiveness of additives as internal lubricants. DSC has also been... 

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