Blooming Antistatic Agents

Blooming antistatic additives fall into fom categories (i) non-ioitic, (ii) anionic, (iii) cationic, and (iv) amphoteric. 

Anionic antistatic agents include the sodium alkyl sulfonates, e.g., RO(S02)ONa, the sulphonamides, e.g., C12H25-N-SO2NH2 (where N is a benzene ring) and the sodium alkyl phosphates, e.g., (RO)2PONa, where R is a long hydrocarbon chain such as stearate. 

Alkyl sulfonates are used at the 2 to 3% level in styrene polymers, unless good clarity must be maintained, in which case ethoxylated amines can be used. Alkyl sulfonates are also employed in rigid PVC, whereas flexible PVC uses high (2 to 6%) levels of ethoxylated amines and fatty acid esters such as GMS. 

Cationic antistatic agents are exemplified by quaternary ammoniinn salts, e.g., R (NR 2) CH2Cr where R is a long alkyl chain and R is a smdl alkyl or aromatic group. They are used in PVC but not generally for food contact. 

Amphoteric antistatic agents include the alkylbetaines. Modest thermal stability usually limits their use. 

---

The effectiveness of blooming antistatic agents is dependent on the relative humidity, and its effects are neither permanent nor necessarily immediate. If they migrate too quickly, they are unlikely to remain effective for long - perhaps a few hours. If migration is too slow, it could take weeks before they can provide protection. Mixtmes of fast and slow types can be used to overcome this. 

Table 4.2 suggests some antistatic dose levels for blooming antistatic agents. 

Table 4.2 Dose levels using blooming antistatic agents ...

Over 50% of the consumption of traditional blooming antistatic agents consists of ethoxylated amines and glyceryl monostearate (GMS), and much of the rest consists of alkyl sulfonates, fatty alkanolamides and amide ethoxylates. Films containing amide antistats usually pass the American Mil-B-81705C (commonly known as Mil spec) test for electrostatic dissipation when the film is a few days old, but not after three or four weeks. This has been attributed to the formation of crystallites of the antistatic agent. 

Permanent non-blooming antistatic agents consisting of neoalkoxytitanates and zirconates have been popularised by Kenrich Petrochemicals under the Ken-Stat name. These substances form bipolar surface layers on the smface, allowing polyolefin films to remain clear after long-term ageing. They are also claimed to be effective in several polymer types, including polyesters and styrene polymers. 

Traditional blooming antistatic agents are facing competition from newer types with more permanent antistatic properties and with the advantage that they are independent of the relative humidity. 

Three properties that contribute the most to migration are (1) incompatibility with the resin, (2) low melt point, and (3) low molecular weight. Examples of noncolorant additives that are prone to migrate are (1) lubricants/dispersants such as metal stearates and bis-stearamides, (2) mold release and slip agents, and (3) antistatic agents. All of these ingredients serve useful purposes in color formulations. If you exceed their solubility limit in the end-use resin, however, you risk blooming and its consequences. 

TransparenL permanent, non-blooming and non-hydroscopic polymers with nano-zirconate antistatic agents, technical paper. Kenrich Petrochemicals, Inc. 

New non-blooming types of antistatic agent have reeently been developed to overcome the deficiencies of the approaches described above. They are generally elassified as permanent antistatic agents because their effect persists, unlike the blooming type, and they do not involve the use of carbon or metallic fillers. 

Ideally, an antistatic agent should be permanent. It should not lose its efifeet, as blooming types do, by migrating too quickly to the surface where it could be removed by washing or abrasion. Its action should be independent of the relative humidity, and it should allow the produet to be light coloured or even transparent, which rules out carbon black. The antistatie agent should not rule out food contact applications. The industry has been addressing these problems, and considerable developments have taken place. 

Croda argues that ethoxylated amides (as opposed to ethoxy lated amines) are effective antistatic agents in polyethylene, but not necessarily in polypropylene. They are said to be faster-acting and more persistent than GMS. The higher molecular weight varieties are free from the volatility associated with another blooming antistat, lauric diethanolamide. 

Example Additives are intentionally added to a polymer to stabilize or improve different polymer properties. They act as antioxidants, UV stabilizers, antistatic agents, flame retardants, etc. However, their migration towards the surface may result in blooming, thereby negatively affecting surface properties that are required for specific applications. TOF-SIMS is ideally suited to characterize surface compositions because it offers molecular information on the uppermost monolayers at high sensitivity. Here, the antioxidant Irgafos 168 (0.3 wt.%) has been analyzed on the copolymer PETi, a poly(ethylene terephthalate (60%) isophthalate (40%)) (Fig. 15.16) [109]. 

Static electricity can be a big problem with carpets. Many carpet fibers therefore incorporate an antistatic agent (such as quaternary ammonium salts or alkyl esters of poly(ethylene glycol) to bleed off static charge. These additives are designed to bloom to the surface of the host polymer reducing the build-up of static charge. 

---