Solid-state extrudability

T300, T50 and PI00 are carbon fibers Spectra 1000 is a gel-spun polyethylene and SSE PE is a solid state extruded polyethylene. Other polymers on die plot have stiff backbones and a liquid crystal character],... 

Table 3. Tensile properties and die swell for different solid-state extruded linear polyethylenes ...

Ultra-oriented solid-state extruded fibres... 

After solid-state processing, a very different crystalline structure was found, compared to melt-processed PHB, as revealed by WAXS and, in spite of a certain orientation due to solid-state processing, a slight decrease of crystallinity was also reported. The mechanical properties of the solid-state extruded PHB depends substantially on the initial molecular weight of the polymer, as well as on the processing temperature, as seen in Tables 22.9 and 22.10. 

Changes in draw ratio and density of both solid-state extruded and melt-processed PHB with temperature. Data taken from [193]... 

Table 2.5 shows a comparison of mechanical properties between steel, aluminum, solid state extruded HOPE, and FIDPE extruded by conventional means. 

Table 2.5 clearly Indicates that the mechanical properties of solid-state extruded HOPE are much superior to the melt extruded HDPE. In fact, the tensile strength of solid-state extruded HDPE is about the same as carbon steel There are some other interesting benefits associated with solidstate extrusion of polymers. There is essentially no die swell at high extrusion ratios (extrusion ratio is the ratio of the area in the cylinder to the area in the die). Thus, the dimensions of the extrudate closely conform to those of the die exit. The surface of the extrudate produced by hydrostatic extrusion has a lower coefficient of friction than that of the un-oriented polymer. Above a certain extrusion ratio (about ten), polyethylene and polypropylene become transparent. Further, solid-state extruded polymers maintain their tensile properties at elevated temperatures. Polyethylene maintains its modulus up to 120°C when it is extruded in the solid state at a high extrusion ratio. The thermal... 

A AH increase with increasing draw ratio k has been found for solid-state extruded and highly drawn pol5miers, and a correlation between indentation anisotropy and Young s modulus has been foimd (4,31). Indentation anisotropy values of several carbon-fiber composites have been reported (32). Recently, the indentation anisotropy of cold-drawn PET, annealed at different temperatures, has also been examined (33). 

A basic element of semicrystalline fibers is the microfibril. Microfibrils are bundled into fibrils, about several hundred nanometers thick. A mechanically weak boundary between the fibrils results in fibrillation during deformation. Barham and Keller [8] and Prevorsek et al. [9] discussed the microfibrillar model, and the latter authors summarized the effects of fiber structure on textile properties. Microfibrils are known to exist in most fibers and are also known to be present in drawn single crystals, such as single crystal PE mats, crazes, melt extrudates and solid state extrudates. In addition, it is known [9] that larger structures, macrofibrils, are composed of microfibrils and that crystallites, disordered domains and partially extended noncrystalline molecules are present in fibers. Fiber structure and properties for nylon 6 and poly(ethylene terephthalate) (PET) fibers were fixrther elaborated [10-13] using both electron microscopy and small angle scattering. A major point of these... 

When the pressure is increased much above 0.23 GPa, stick-slip extrusion occurs. At an extrusion pressure of 0.23 GPa, the extrusion stops when the viscosity increases sufficiently that the extrusion force cannot overcome the resistance to extrusion. During slip in stick-slip extrusion, a spiral fractured extrudate is produced that is similar to spiral products found in shear fracture of polymeric melts during extrusion (12). The flow profile in the solid state extruded rods is a deep shear parabola (10, 13, 24) (Figure 2) which suggests that stick-slip may arise from shear fracture of the extrudate. 

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. 

Figure 8 Degree of erystallinity, calculated from differential scanning calorimetry) for solid-state extruded samples of linear polyethylene with average molecular weights of(0) 59,000, (A) 71,000, ( ) 92,000, and (A) 147,000. (From Ref 39.)...

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