Processing Aids
During extrusion it is desirable to extrude the material as rapidly as possible. This process is limited by shear the thermal degradation and melt fracture. Wax-like processing aids reduce melt viscosity and increasing processing rates. (RDC, 7/29/2008) (Chapman and Oriani, US Patent 7,390,848; 6/24/2008)
Processing aids such as fluoropolymers are often used to reduce the effects of melt fracture during melt processing and improve production rates. However, fillers and additives may block the effect of the processing aid and reduce the critical shear stress to unacceptable levels. Cernohous et al countered this effect with coupling agents such as grafted polyolefins, block copolymers and silanes. These coupling agents reduced the interfacial tension between the binder and the interfering agents such as wood flour. This permits the processing aid to be effective and reduce melt fracture. The coupling agents may also improve water uptake, flexural modulus and tensile strength. The example is a high density polyethylene containing 20 to 70 wt% wood flour, 0.1 to 1.0 wt% of a fluorocarbon processing aid and 0.1 to 2.0 wt% coupling agent consisting of a mixture of block copolymers and a maleated polyethylene. (RDC 8/29/2008) (Cernohous et al, US Patent 7,402,625; 7/22/2008)
Recent US Patents
11
Recent Journal Articles
Study of Effects of Processing Aids on Properties of Poly(lactic acid)/Soy Protein Blends
(239-247) Journal of Polymers and the Environment 19 #1 (2011)
Liu, Jiang and Zhang of Washington State University, Washington, studied two processing aids, acetyl tri-n-butyl citrate and an alkene bis fatty amide (wax) and their effects on poly(lactic acid) (PLA)/soy protein concentrate blends. Acetyl tri-n-butyl citrate and alkene bis fatty amide played different roles in improving the processability of the blends, with the former functioning as a plasticizer for PLA and the latter as an internal/external lubricant. The amide wax was more effective in reducing blend melt viscosity through its dual functions of internal and external lubrication. Acetyl tri-n-butyl citrate displayed a stronger effect in facilitating PLA nucleation than the amide wax. Both processing aids decreased tensile strength and modulus of the blends and increased break strain and impact strength. (RDC 4/22/2011)