MATERIALS | HIGH PERFORMANCE COMPOUNDS
dosage levels from about 0.1% to about 5%. Aside from modulus, Hybrid’s Dodecaphenyl MS0802 and Trisilanol phenyl SO1458 high temperature POSS additives show similar proper- ties to those of aromatic thermoplastics. The Young’s modulus of silsesquioxane cages is around 10 GPa, which lies between that of high-perfor- mance semicrystalline polymers (in the order of 5
GPa) and filled polymers (20-40 GPa). This means that phenyl bearing POSS additives provide rheological diluency during melt processing without permanent plasticisation effects (the high processing temperatures of aromatic thermoplas- tics limits the use of traditional plasticisers due to their propensity to degrade during compounding). The phenyl groups on the trisilanol phenyl POSS
interact strongly with the aromatic groups of the polymer backbone, according to the company, while the silanols afford interfacial compatibility and dispersion of high value fillers and ingredients such as pigments and various functional additives. Coupling agents used for surface modification
are often not suitable for high temperature com- pounding. But the silanols of trisilanol phenyl POSS form covalent bonds to surfaces; it can therefore serve both as a dispersion agent and rheological modifier.
Structural schematic of Hybrid Plastics’ high temperature dodecaphenyl POSS (MS0802) processing aid (left) and trisilanol phenyl (SO1458) processing and dispersion additive Source: Hybrid Plastics
Flow
enhancement of PES melt blends measured by extruder torque using Hybrid Plastics’ dodecaphenyl (DP) and tri- silanol phenyl (TSP) POSS additives at different loadings
Source: Hybrid Plastics
Right: This image of clear extruder strands at the die indicates good disper- sion and compatibility of POSS with the resin
POSS mechanism Lichtenhan and Morgan say the mechanism by which POSS enhances flow in polymers without degrading thermal or mechanical properties is not entirely understood. Recent studies of POSS-PES melt blends support the hypothesis that POSS works at the molecular level to reduce polymer chain entanglement, thereby reducing viscosity (Figure 1). The overall weak nature of the interac- tions between POSS molecules and PES chains allows the POSS nanoparticles to function as lubricants, but the relatively stronger interactions of TSP-POSS allows it to disperse at a finer level and provide greater processability enhancements. Flow enhancements using trisilanol phenyl POSS
(TSP) are observed in PEEK, PPSU, PEI, FEP and related platforms. The different levels of viscosity reduction across polymer platforms may be due to differences in polymer-POSS interactions, entan- glement molecular weight, or molecular weight distributions within various resin platforms. The incorporation of phenyl-bearing POSS at additive levels into high temperature polymers is said to result in melt processability improvements as evidenced by reduction of extruder torque or increases in MFI. The high temperature stability without volatilisation of these additives is advanta- geous as is the ability to retain modulus and Tg after processing, according to Hybrid Plastics. Meanwhile, at Quarzwerke division HPF The
Mineral Engineers, Project Manager Thorsten Hilgers has been carrying out tests with different high-performance fillers, mostly surface-treated, in PA 6T-6, polysulphone and polyphenylene sul- phide. These three polymers all have processing
56 COMPOUNDING WORLD | November 2021
www.compoundingworld.com
IMAGE: HYBRID PLASTICS
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