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ADDITIVES | PROCESSING AIDS


Figure 6: Schematic showing (left) i-Octyl POSS plasticising lubricant and (right) high temperature phenyl trisilanol surfactant processing additive


Source: Hybrid Plastics


performance of existing polymer formulations has become a growth area within the speciality chemicals industry. This trend is now extending to processing, lubricant and surfactant additives. Our customers always want more performance from their additives and this means they ask for a single additive that can provide a combination of desirable effects that were previously only achievable through careful formulation from multiple different ingredients,” Lichtenhan says.


Formulation challenges One of the longstanding problems has been that polymers often remain plasticised from processing aids and die lubricants, he says. “This creates a challenge for formulators and material engineers because the residual effect must be accommodat- ed for. The time dependent plasticiser migration and volatility further complicates the performance assurance of final parts. In several cases we have had customers replace traditional processing aids and lubricants because they negatively impacted the high temperature durability of moulded parts. The replacement of these additives with advanced additive technologies enabled more competitive and upgraded product to enter the market. In some cases, even new performance standards were achieved.” Additives that afford rheological control, colour dispersion and nucleation control of high performance aromatic thermoplastics is the focus for Hybrid Plastics. A particular growth area is in the use of polymers such as PPS, PEEK, PEI and PPE for 3D filament printing. Such polymers are challenging to mould using traditional methods. However, the absence of injection pressure and layer deposition limitations in 3D print systems provides additional hurdles for high molecular


68 COMPOUNDING WORLD | April 2019


weight grades of these polymers. Hybrid Plastics says that its POSS processing additives and compatibilisers based on silesquiox- anes provide the basis for its solution platforms. “The precisely defined composition and topologi- cal features of this chemical family are unique from traditional chemical additives by providing an envelope of desirable effects. The effects are derived from the rigidity of the inorganic central core, which enables large molecular surface area and volume contributions to formulations. Exter- nally, each core silicon atom contains an organic group for compatibility, plasticisation, reinforce- ment or reactivity. POSS additives are also well suited for masterbatching. Typical let-down dosing levels range from about 0.1% to about 5% relative to resin,” says Lichtenhan. “The high processing temperatures of aromatic thermoplastics also limits the use of traditional plasticisers due to their propensity to degrade and volatilise during compounding. In such instances the phenyl POSS trisilanol provides an envelope of effects. The phenyl groups strongly interact with the aromatic of the polymer backbone and the silanols afford interfacial compatibility with other ingredients such as colour additives. In this respect, POSS silanols are similar to a surfactant molecule,” he says.


Engineering options Processing aids for engineering thermoplastics (PE/ PP) and elastomers are often sought from Hybrid Plastics. “Low migration additives are highly desired in these systems and in some cases a secondary process of crosslinking is also utilised,” Lichtenhan adds. “POSS additives containing reactive groups, such as vinyl, can be utilised. The crosslinking capability of olefinic POSS greatly aids


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