The flow behavior and the effect of the spinning conditions on the fiber properties and structure of poly(ethylene terephthalate) modified with 60 mol% p -hydroxybenzoic acid (PET/60PHB) were investigated. PET and its...
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The flow behavior and the effect of the spinning conditions on the fiber properties and structure of poly(ethylene terephthalate) modified with 60 mol% p -hydroxybenzoic acid (PET/60PHB) were investigated. PET and its copolyesters with 28 and 80 mol% PHB were used as control samples. The melt of PET/60PHB at temperatures above 265°C exhibited extremely low viscosity and low flow activation energy. High birefringence, indicating the presence of a mesophase, was observed between 265 and 300°C on a hot-stage polarizing light microscope. The maximum tensile strength and initial modulus, 438 MPa and 37 GPa, respectively, were obtained at 275°C for a 0.69 IV polymer. The fiber strength and modulus were significantly lowered when extrusion was conducted at temperatures below 265°C. The fiber properties could also be improved when a high extrusion rate and/or a high draw down ratio was used. Scanning electron microscopy revealed that the fibers spun at temperatures above 265°C had a well-developed, highly oriented fibrillar structure. The fibers spun at lower temperatures, however, were poorly oriented and nonfibrillar in character. The high orientation and superior mechanical performance achieved at high temperatures were attributed to the presence of the nematic mesophase in the polymer melt.
For the past several years the production of high-modulus, high-strength polymeric materials has received increasing attention by many researchers. Generally, in the commercial processes for converting polymers to fib...
For the past several years the production of high-modulus, high-strength polymeric materials has received increasing attention by many researchers. Generally, in the commercial processes for converting polymers to fibers, the modulus and the strength of fibers produced is very low; for example, 1/50 to 1/100 of the corresponding theoretical values [1, 2]. The presence of defects and chain folds leads to stress concentration on relatively few tie chains. This stress concentration has limited the attainment of high modulus [3]. Therefore, if a high-modulus fiber is to be achieved, an oriented extended-chain-type crystal structure relatively free from folds must be obtained [4].
The effects of pressure on the compressibility and crystallization of three fiber-forming polymers, poly(tetramethylene terephthalate), nylon 66, and Qiana® nylon, have been studied. The Instron capillary rheomet...
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The effects of pressure on the compressibility and crystallization of three fiber-forming polymers, poly(tetramethylene terephthalate), nylon 66, and Qiana® nylon, have been studied. The Instron capillary rheometer was adapted as a high-pressure dilatometer for all the high-pressure experiments. The compressibility results reaffirmed that polymers are highly compressible, and their compressibilities are nonlinear at temperatures above the glass transition temperatures. polymer melts show higher compressibility than do polymers in the solid state. The kinetics of crystallization of these polymer melts under high pressures were studied. Analysis of the data revealed low Avrami exponents at high pressures. It seems that the kinetics of crystallization of these polymers from the melt under high pressure are different from those at normal pressure. Crystallization temperatures of these polymers were also measured. The crystallization temperatures are considerably higher at higher pressures.
AbstractThe flow behavior of four cellulose acetate–acetone solutions varying from 20.00% to 28.18% solids concentration was observed using flow visualization techniques at 24°C with an industrial‐type dry spin...
AbstractThe flow behavior of four cellulose acetate–acetone solutions varying from 20.00% to 28.18% solids concentration was observed using flow visualization techniques at 24°C with an industrial‐type dry spinning system. Fibrous particulate matter entertained in the solutions and crossed polars revealed the streamlines and the birefringence due to flow in glass spinnerets. The streamlines of the four solutions were radially convergent at all obtainable throughputs. The crossed polars revealed a cone of birefringence with the order of the interference colors decreasing upstream of the capillary inlet. The intensity and extent of birefringence varied somewhat with concentration and throughput. Except for kneeing, the emerging extrudates were undeformed. The kneeing was not a result of flow instability a t the capillary inlet but was due to another, undetermined instability. A separate study of the kneeing revealed both a concentration dependence and hysteresis. The birefringence of the emerging extrudates was a function of both concentration and throughput, and it yielded some information about the structure of the solut
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