Glass transition filaments

A single screw extruder was used to fabricate the filaments from the composite. The glass transition of the composite was found to be 126°C, which is higher than that of pure ABS material. In addition, the melt flow behavior was extensively studied by setting up a finite element model (79). 

Polymeric filaments produced in this way have a diameter of 100 to 300 fim and show anisotropy in their properties, indicating molecular orientation. For instance the birefringence of this fiber is 0.0073. Table 1 compares the modulus measured both in axial and in lateral direction, with the modulus of the same material cured under isotropic condition at 80 C. The increase in modulus in axial direction is obvious. The decrease of the modulus at higher temperatures can be ascribed to both the glass transition and melting of crystalline areas. 

This polyborazine (3) could be melt spun but it was impossible to draw and wind the crude filaments on a spool. This behaviour is related to the high glass transition temperature of this polymer (Tg = 180°C) which probably reflects a high degree of polymerisation and/or reticulation. The irregular crude fibres were pyrolysed into BN filaments (Fig. 2) under similar conditions to those described for polymer (1) pyrolysis. 

Elastin, which is substantially amorphous but fibrous at all levels of investigation (starting from the largest filaments which are about 6 fim in diameter and down to about 10 nm (17,18)), is a fragile, glassy substance when dry and has a glass-to-rubber transition temperature at about 200 C (19) upon hydration or solvation with appropriate solvents, it becomes a rubbery system with the glass transition below room temperature (20). 

Considering melt flow of BC, it is usually assumed that the test temperature is UCST > T > T, where T stands for glass transition temperature of the continuous phase. However, at Tg < T < T g (T g is Tg of the dispersed phase) the system behaves as a crosslinked rubber with strong viscoelastic character. At UCST > T > T, the viscosity of BC is much greater than would be expected from its composition. The reason for this behavior is the need to deform the domain structure and puU filaments of one polymer through domains of the other. Viscosity increases with increase of the interaction parameter between the BC components in a similar way as an increase of the interfacial tension coefficient in concentrated emulsions causes viscosity to rise [Henderson and Williams, 1979]. 

A polymer normally used as a fiber may make a perfectly good plastic if no attempt is made to draw it into a filament. Similarly, a plastic, if used at a temperature above its glass transition and suitably cross-linked, may make a perfectly acceptable elastomer. In the following text, a brief account of some of the more common plastics, fibers, and elastomers is given. The classification is based essentially on their major technological application under standard working conditions. 

As reviewed, the mechanical properties of centrifugally molded pipe and 55° filament wound pipe are much more resin dependent than typical custom engineered pipe. With centrifugally cast pipe, the tensile properties are very resin dependent because the fibers are chopped into relatively short lengths. It is subjected to creep and time-loss of mechanical properties. In addition, resin properties drop radically with temperature especially near the glass transition temperature. 

Structure deduced from the distinct four point pattern observed in samples which were annealed after drawing. For cold drawn polymers the assumption of a single phase structure implicit in the aggregate theory may therefore be valid. Some of the materials to which the aggregate theory has been applied were hot stretched (i.e. drawn above the glass transition temperature), but the annealing in these cases would be far from complete, since the temperature was maintained for a relatively short time, and the filaments were always under tension. Thus again a distinct two phase structure may not have been well developed. 

The variation of compliances with draw ratio for cold drawn polypropylene filaments examined at 20°C appeared very similar to that of high density polyethylene, with an increase in all compliances but Sii, which was insensitive to draw ratio. Ward aggregate theory was not applicable except for low draw ratios, implying that other processes intervened in addition to an orientation of pre-existing units. It was probable that even above the glass transition temperature increasing orientation led to a reduction in molecular mobility, as was known to occur in polyethylene terephthalate. ... 

In 1956 Thompson and Woods reported that dynamic experiments in extension indicated that orientation increased the temperature of the p transition, about 80°C, for oriented crystalline fibres, and reduced the drop in modulus occurring at higher temperatures. Subsequently nuclear magnetic resonance was used to demonstrate that orientation reduced molecular mobility above the glass transition temperature. Measurements of dynamic extensional and torsional moduli of hot stretched filaments and films were reported in 1963 by Pinnock and Ward, who found that the relations between measured compliances below the glass transition temperature were consistent with the deformation of an incompressible elastic solid. 

Vinyl ester resins are similar to unsaturated polyester resins in that they are cured by a free radical initiated polymerisation. However, they differ from the polyesters in that the unsaturation is at the ends of the molecule rather than along the polymer chain. Unlike polyesters, vinyl esters show a greater resistance to hydrolysis as well as lower peak exotherm temperatures and less shrinkage upon cure. Cured vinyl ester resins exhibit excellent resistance to acids, bases and solvents. They also show improved strain to failure, toughness and glass transition temperatures over polyesters. They can be used in filament winding, pultrusion, resin injection, vacuum moulding and conventional hand lay-up. 

In the second variant of SHMM the investigated filaments were subjected to tensile stresses with different values under certain constant temperatures. The simultaneous heat mechanical samples modification was carried out using an apparatus created in our laboratory. The device involves a movable cylindrical oven located on the horizontal rails and a setup for the sample deformation reading. The heat-mechanical treatment begins when the preheated oven was rapidly shifted around the studied PET bundle that was simultaneously stretched with the needed strain stress. The experiment involves annealing of an as-spun PET yarns at four different temperatures in a narrow temperature range from 80 "C to 95 "C closely above its glass transition temperature while they are subjected to a well-defined tensile stress. 

Cyanate esters are used in the manufacturing of structural composites such as filament winding, resin transfer molding, and pultrusion. The cyanate ester resins have shown superior dielectric properties and much lower moisture absorption than any other structural resin used for composites. The glass transition temperature of cyanate esters is relatively high (250°C), but it requires cure temperatures greater than 177°C. 

In this research work, we used thermally sensitive SMPU filaments in the fabric stmcture. The of a thermal SMP can be of the glass transition type where the SME could be seen over a range of temperature. Different amounts of recovery stress could be generated for such SMPs by changing temperature over a range. This clearly... 

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