Ultrahigh extrusion

Ultrahigh-molecular-weight epoxy resins can be used directly as a thermoplastic adhesive. The hydroxyl groups and good wetting characteristics provide for good adhesion to many surfaces. These adhesives are prepared in film form by solvent casting or extrusion. 

The predominant system for controlle-rheology reactive extrusion is polypropylene (PP) with systems such as ultrahigh-melt-flow polypropylene, high-impact polypropylene blends... 

The results described above for highly drawn samples of HDPe (EDR > 12) seem to be consistent with such an assumption. However, in some cases, the important role of the shear vs. extensional deformation components (JO. In extrusion of spheruiitic HOPE and the compressive force in extrusion of powders of polyethylene single crystals (21) and ultrahigh MW polyethylene (22) has been suggested. Indeed, we have shown (23) recently that single crystal mats of various poiyethyienes, which couid not be extended by tensile force below can be effectively drawn even at room temperature up to... 

Zachariades, A. E., Mead, W. T. and Porter, R. S. (1979) Recent developments in ultramolecular orientation of polyethylene by solid state extrusion, in Ultrahigh Modulus Polymers (A. Ciferri and I. M. Ward, eds), p. 77. Applied Science Publishers, London. 

Viscosity is affected by the discussed additives in different ways. Figure 10.36 shows a marginal decrease in viscosity with concentration. Addition of ultrahigh molecular weight silicone additive, which is used as a mold release, decreases viscosity of polyethylene melt and thus lowers energy input in extrusion (Figure 10.37). Addition of 0.2 wt% of silicone additive reduced Brabender torque by 40%, elongational viscosity by a factor of four, and increased spiral mold flow by 30%. ... 

Polydimethylsiloxanes are frequently used in formulations for extruded materials, mostly to improve slip properties. It should be noted that addition of ultrahigh molecular weight, UHMW, polydimethylsiloxanes also affects process parameters, such as barrel pressure (Figure 13.5), and amperage (Figure 13.6) in single screw extrusion. ... 

Ren X, Wang XQ, Sui G, Zhong WH, Fuqua MA, Ulven CA. Effects of carbon nanofibers on crystalline structures and properties of ultrahigh molecular weight polyethylene blend fabricated using twin-screw extrusion. J Appl Polym Sci 2008 107 2837 5. 

This section deals with semicrystalline thermoplastics that cannot be processed by the techniques described earlier. Perkins and Porter (22) have reviewed the solid state deformation of polymers in detail and describe the numerous reports of solid state extrusion. Aharoni (23) has reported that a number of polymers may be solid state extruded to high draw ratio (> 10) by the conventional process. These include HOPE, poly(ethylene oxide), poly(4-methyl pentene-1). Polypropylene is also readily extrudable (24). However, there are many other polymers that would be attractive if they could be obtained in high draw, particularly the established fiber-forming polymers such as the nylons and poly(ethylene terephthalate). The ma,ximum extrusion draw ratio that has been reported for nylon 6 is 5 (25). This has been attributed to the onset of strain hardening at much lower extensions than polyethylene (10). Ultrahigh molecular weight polyethylene is also of interest as a way of improving the mechanical properties. 

IJe have attempted to extrude nylon 11, poly(ethylene tereph-thalate) (PET) and ultrahigh molecular weight polyethylene (UHflWPE). The billets were prepared by slow cooling from the melt. The results are summarized below. Nylon 11 was extruded up to draw ratio 5 in the presence of silicone oil lubricant. Both high molecular weight PET and UHMWPE could not be extruded at this draw ratio. Use of the split billet and push-pull techniques did not assist the extrusion. For the purposes of this discussion these polymers will be described as "unprocessable". 

M.P.C. Watts, A.E. Zachariades and R.S. Porter, "New Methods of Solid State Extrusion Applied to Ultrahigh Molecular Weight Polyethylene - Processing and Properties", in preparation. 

Polyethylene may be extmded below its melting point if sufficiently high pressures are exerted, in which case the process is known as solid-state extrusion. If the starting material is a reduced entanglement precursor, such as solution-grown crystals [56] or as-polymerized granules [57], fibers and tapes with ultrahigh... 

---