Slip additives

Slip additives are incorporated directly into the polymer during the extrusion process. They work by migrating to the surface as the polymer cools, forming a solid lubricating layer at the surface, lowering the friction or reducing adhesion between contacting polymer surfaces and the polymer and other materials. 

Erucamide and oleamide are the most commercially important slip additives. It is generally considered that oleamide blooms to 

These are, in effect, external lubricants that operate in the solid state. The most commonly used slip additives are fatty acid amides such as erucamide. These additives are used to prevent blocking in thin films of polymer, e.g., sticking together of thin film bags. 

It is common for aliphatic amides to be incorporated into plastics, particularly polyethylenes, to act as slip additives. 

It is possible to use LC-MS to detect these types of slip additives in plastic samples. Using the LC-MS conditions described in Section 6.2, it is possible to detect Behenamide (mixture of two aliphatic amides of molecular weight 331 and 339) and erucamide (molecular weight 337) in solvent extracts of polyethylene and polypropylene. 

It is also possible to use GC and GC-MS to analyse these and another common slip additive oleamide in extracts from plastics as they have sufficient volatility to elute from the GC column. 

Amides dispersed in melted PE at RT, at levels exceeding their solubility, migrate to the PE surface during and after the blowing of films. Exuded amides form random aggregates on the film s surface that reduce the close contact and cohesion between adjacent sheets. Slip or antiblock activity increases upon increasing the amount of amide on the PE surface until a critical level is reached thereafter, further increase of the surface amide concentration does not improve the slip or antiblock properties and may produce an undesirable oily layer on the film. 

The most effective amides are solids at RT, which may form crystals on the film surface and diffuse rapidly from the PE surface. 

The fatty amides used in PE production include erucamide (EA) cis-13-docosenoic acid, amide), behenamide (docosenoic acid, amide), oleamide (OA) and stearamide (SA) [43]. Unsaturated amides, such as EA and OA, provide superior slip properties, whereas saturated amides, such as behenamide and SA, provide acceptable slip and superior antiblocking properties. EA displaced OA as the preferred slip agent for the production of PO film because it melts at a higher temperature and is more stable at extrusion temperatures EA can be used as a slip and antiblock agent [45]. SA also provides useful slip properties, although it is slower acting it has superior antiblock properties to those of EA and OA. 

Primary fatty amides are the preferred slip agents and are added at an approximate level of 0.1% during the production of LDPE film materials (in the USA, PE film production was 6.3 billion poimds (lbs) in 1991) [46]. They are less frequently used as antiblock and mould release agents in the manufacture of other flexible and rigid plastic products. EA, OA and SA are very cost-effective for these applications and hence are widely used however, other saturated and unsaturated amides with a chain length of 18-22 carbon atoms may be equally effective [47]. 

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Analysts in industry prefer in many cases to maintain consistent methods for their analyses. Recommended ASTM analytical procedures are quite well developed in the rubber and polymer industry. As an example, we mention the standard test method for determination of phenolic antioxidants and erucamide slip additives in LDPE using liquid chromatography [76]. However, the current industry standard test methods (ASTM, AOAC, IUPAC, etc.) use a large number of solvents in vast... 

ASTM D 1996-97, Standard Test Method for Determination of Phenolic Antioxidants and Erucamide Slip Additives in Low Density Polyethylene Using Liquid Chromatography (LC), Annual Book of ASTM Standards, ASTM, West Conshohocken, PA (1997), Vol. 08.01. 

Various additives in PE (Santonox, Nonox DPPD, Neozone A, Ionol and Agerite White) were determined by conventional TLC [507]. Other additives in PE, studied by means of TLC, were Tinuvin P 120/326/327/770, Cyasorb UV531, Anti UV P (2-hydroxy-4-n-octyloxybenzophenone), Irganox 1076, Sanduvor EPU, AO-4 and Dastib 242/263 [508], TLC has also been used in the analysis of additives in polyurethanes [509,510] as well as of slip additives (ethoxylated amines and amides) in HDPE extracts... 

An example of multidisciplinary analysis is the study of the performance of antistatic and slip additives in polyolefins, as investigated by means of XPS,... 

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. 

Antiblock additives are often incorporated into packaging films to prevent them sticking together. Their effectiveness relates directly to the roughness they impart on a film surface while minimising loss in optical properties. They are often used in association with slip additives such as erucamide. Common antiblock additives include crystalline silica, diatomaceous earth and talc (magnesium silicate). 

To examine slip additive concentrations in packaging films (typically 300-700 ppm), solvent extraction is used to remove the additive from the film. Hexane/ isopropanol (30/70 v/v) can be used to extract oleamide (fast bloom slip), stearamide and erucamide (slow bloom slip) from polyolefin films. GC or LC-MS is then employed to analyse the concentration of the extracted slip additive. 

IR internal reflection spectroscopy can be used to distinguish the relative differences in the concentration of the slip additive at film surfaces. 

Slip additives act at the surface of a polymer film or article to reduce the friction between it and another surface. In a variety of plastics, such as polyolefins, polystyrene, and polyvinyl chloride, fatty-acid amides are applied as slip additives. Fatty-acid amides, such as oleamide, stearamide, erucamide, and oleyl palmitamide, are added to plastic formulations where they gradually tend to bloom to the surface, imparting useful properties including lubrication, prevention of films sticking together, and reduction of static charge. 

Three theories were proposed to explain wall-slip (a) adhesive failure at the wall, (b) cohesive failure within the material as a result of disentanglement of chains in the bulk and chains absorbed on the wall, and (c) the creation of a lubricating surface layer at the wall either by a stress-induced transition, or by a lubricating additive. If the polymer contains low molecular weight components or slip-additives, their diffusion to the wall will create a thin lubricating layer at the wall, generating apparent slip. 

We should note at this point, however, that if one of the components is a low molecular weight material (e.g., certain antioxidants, foaming agents, dyes used for fibers, or slip additives), molecular diffusion may be a significant factor in the mixing process. 

Antiblocking agents, slip additives Silica, amide waxes, oleamide... 

R. Moreno, The Role of Slip Additives in Tape-Casting Technology Part I - Solvents and Dispersants , Am Ceram. Soc. Bull., 71 [10] 1521-31 (1992). 

Figure 83 Comparison of coefficients of friction of the surfaces of treated and untreated films at different concentrations of slip additive...

Rare earth addition and rapid solidification processing might result in (i) grain refinement and (ii) development of fine incoherent dispersoids leading to dispersed slip. Addition of dispersoids such as Er203 and Ce2S3 to Ti3Al(Nb) alloys produces refinement... 

Excessive noise in gears and transmissions is often related to frictional problems, especially friction-induced oscillations or stick-slip. Addition of molybdenum disulphide can sometimes reduce the friction problems. An example was... 

The polyester type polyols used in polyurethane laminating adhesives are produced by the direct esterification of polyfunctional carboxylic acids and glycols. Polyester polyols provide the soft segment in polyurethane products giving the adhesive flexibility. Ester groups of the polyol also contribute to adhesion. Polyester polyols provide limited wetting and adhesion of olefinic surfaces with amide slip additives (in contrast to polyether polyols). Typical examples include adipic acid, caprolactone, maleic acid and isophthalic based polyester polyols. 

Mar and slip additives Wetting agents Dispersants Cosmetics... 

Use Slip additives for PVC and polyolefin resin films, antistatic and antifogging agent for clear plastic wraps, and as internal lubricants. 

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