Heat Shrinkage Research Articles

CHANGES OF THE PROPERTIES OF KEVLAR TIRE CORDS INDUCED BY STEAM- AND DRY-HEAT TREATMENT AND FATIGUE

(1) The tensile strength and ηinh of Kevlar tire cord decreased markedly by steam-heat treatment above about 160°C for 1 hr., but they did not change by dry-heat treatment at 200°C for 1 hr. The specific gravity increased with the increase in treating temperature. From these results, it was concluded that the decrease in the degree of polymerization by hydrolysis and the change of fine structure of the steam-heat treated Kevlar tire cords are the causes for the decrease in the tensile strength and fatigue resistance.(2) Heat shrinkage of Kevlar tire cords was lower than that of nylon 6, polyester and rayon tire cords. Change of X-ray wide angle diffraction pattern in steam-heat treated (tensionless state) Kevlar filaments was very small as compared with that of nylon 6 filaments. On the other hand, we found by DTA and TGA analysis that the decomposition of Kevlar begins at about 500°C and it decomposes at about 605 C. From these results, it was considered that the change of entropy (ΔS) in Kevlar by heat is very small as compared with that of nylon 6, because the molecular conformation of Kevlar is in trans-form and has extended-chain structure with very little flexibility.(3) a: We observed the fibrillation of Kevlar filaments at the fracture after fatigue test and also at the broken area of the Kevlar tire cords which were tested after steam- and dry-heat treatments by the tensile strength test.b: Fatigue resistance increased with increasing twist of Kevlar tire cords, but the tensile strength decreased with increasing twist.c: During fatigue test, the temperature of the air in rubber tube samples which contain Kevlar tire cords was lower than that of polyester tire cords and was equal to that of nylon 6 tire cords.

Distribution of some physical properties in injection‐molded thermoplastic parts

AbstractDuring the injection molding process, moldings undergo shear and elongational stresses. They are also exposed to thermal gradients of varying intensity. Invariably, molded parts, or at least some sections thereof, freeze before the polymer chains can relax to a random, non‐oriented configuration. As a result, injection molded parts contain frozen strains and exhibit anisotropic physical properties. In the present work, a variety of experimental techniques have been employed to determine the three‐dimensional variation of the following properties of injection‐molded, thermoplastic, rectangular parts: density, heat shrinkage, birefringence, and tensile strength.

Radiation induced-grafting of acrylic acid onto polyvinyl chloride fibers

The grafting of acrylic acid in aqueous solution to polyvinyl chloride fibers has been studied in the presence of ferrous, ferric, and cupric salts. The mutual irradiation technique was adopted using a Co-60 source or a Van de Graaff accelerator. The grafting and homopolymerization were suppressed by the cations. Particularly the grafting was suppressed by the cations in the following order of effectiveness : Cu 2+>Fe 2+>Fe 3+. The rate of grafting (in %/hr) was proportional to the 0.76th power of the dose rate over the range from 8.5 × 10 3 rad/hr to 1.4 × 10 5 rad/hr. The apparent activation energy for the grafting was determined to be 6.1 Kcalmole between 25° and 75°C for the mixture of AAH 2O(CH 2Cl) 2, containing Mohr's salt, 4 × 10 −3 mole/l. The grafted polyvinyl chloride fibers showed considerable improvement in moisture regain, heat shrinkage, and melting properties.

RADIATION-INDUCED GRAFTING OF ACRYLONITRILE ONTO POLY (VINYLIDENE CHLORIDE) FIBER

Experiments have been undertaken to graft acrylonitrile onto poly(vinylidene chloride) fiber for the purpose of modifying properties without serious loss of flame-retardance of the original fiber.The grafting took place smoothly when a suitable swelling agent such as dimethylformamide was used as a medium for the immersion grafting of acrylonitrile by a simultaneous irradiation technique. In most cases, 1:1 mixture of acrylonitrile and dimethylformamide was employed for the reaction and degree of grafting higher than 100% was achieved without difficulty.Some properties of the graft fibers were measured. The density of poly(vinylidene chloride) fiber is about 1.70, which is the highest among common organic fibers; the value becomes lower by the grafting and the fiber of 100% graft shows a value of 1.40, which is similar to that of polyester. The initial Young's modulus of th fibers increases with grafting. Fiber with 33% graft shows a value of 239 kg/mm2, which is 2.5 times greater than that of the original fiber.With increasing degree of grafting, the extent of heat shrinkage becomes less and at about 100% graft, the fiber form is retained even at 300°C. Graft fibers are self-extinguishing so long as the graft percentage is less than 74% (Cl content is greater than 43.3%). In the case of poly (vinyl chloride) fabrics grafted with acrylonitrile, the threshold graft percentage is much lower than the poly(vinylidene chloride) grafts and has a value of about 36% which corresponds to a Cl content of about 42%. It seems that 42-43% Cl content is the common threshold for the self-extinguishing of poly(vinylidene chloride) and poly(vinyl chloride) fibers grafted with acrylonitrile.

Effect of shortening during cooking on the tenderness and histology of beef

AbstractIn muscles which have gone into rigor at 15°C or 37°C without shortening, prevention of cooking shortening leads to greater toughness than in samples cooked free. This tenderness difference is not seen in cold shortened muscles. A histological study showed that heat shrinkage of collagen imposes an irregular “cooking crimp” in unshortened muscle, cooked free. This is quite distinct from cold induced crimp. Cooking cold shortened muscle under restraint completely removes the cold crimp. A striking “crossed‐diagonal” orientation of the perimysial collagen in the cooked meat is described.

Laboratory Modeling of Garment Fires1

In an attempt to model real-life burn accidents, garment assemblies were burned on adult-size mannequins and the temperature distribution over the mannequin surface determined. Anaesthetized, shaved rats were exposed in openings of the mannequinns in the spatial arrangements encountered in real-life garment fires. The correlation between the depth of burn into the skin and the temperature observed on the mannequin surface near the exposed skin seemed fair. In other experiments, the interaction of burning fabrics and depth of burn was studied by means of simulated garments fitted to anaesthetized, shaved rats. Garment geometry was found to affect the burn injury potential as much as fabric parameters. It is discussed in terms of initial fabric to skin, fabric to mannequin, and outerwear-underwear distance (these distances often change during the fire due to heat shrinkage of thermoplastic fibers, turbulence, etc); formation of chimney spaces between fabric layers and the mannequin surface; and firestops such as belts. Other experiments covered the effect of combinations of various fabrics, such as dress-slip assemblies. Garments made from flame-retardant (FR)-treated cotton fabric and 100% thermoplastic fibers did not ignite in our experiments when used as single layers. When combined with polyester/cotton blends in outerwear-underwear assemblies, these fabrics caused smaller areas of the mannequins to be raised to elevated temperatures than the blend fabrics alone. This effect was particularly marked for the FR treated cotton. In our experiments, polyester/cotton blends seemed to have more potential for causing injury than comparable, 100% cotton fabrics. 100% thermoplastic fiber fabrics appeared to have a low injury potential. The effect of fabric weight on the area of the mannequin raised to elevated temperatures was not clear cut, though it was obvious that heavier fabric caused more severe injury to exposed skin, and were more difficult to extinguish by beating out the flames, than light fabrics.

Effects of molding conditions on properties of injection‐molded polycarbonates

AbstractStatistically designed experiments were carried out to study the effects of molding conditions on the properties of two types of polycarbonate, which were synthesized by the solvent process and the melt process, respectively. The properties tested in this study were classified into two groups with respect to the effect of molding conditions. One, which included birefringence, heat shrinkage at 180°C, and surface resistance to Taber abrasion, was mainly affected by stock temperature and was slightly affected by holding pressure. The other, which included resistance to solvent crack, Rockwell hardness, density, and heat shrinkage at 120°C, was affected by mold temperature and holding pressure. Mechanically isotropic moldings with a low degree of frozen orientation could be molded at a high stock temperature and at a low holding pressure, where stock temperature was more effective than holding pressure. Moldings with low residual stresses could be molded at a high mold temperature and at a low holding pressure. Essentially there was no difference in the molding conditions and properties by the method of synthesis. However, under the same molding conditions polycarbonate synthesized by the melt process gave a higher degree of frozen orientation and somewhat more rigid moldings.

MODIFICATION OF SYNTHETIC FIBER BY THE GRAFT COPOLYMERIZATION OF REACTIVE MONOMER

Acrylic acid was graft copolymerized onto polypropylene fiber and fabric using Co60 γ-ray preirradiation method.As the grafted polypropylene has reactive groups such as caroboxyl groups in the grafted side chains, some aftertreatments including cross-linking can be achieved using these reactive groups.Some properties of the acrylic acid grafted and aftertreated polypropylene fiber and fabric were examined.The results are summarized as follows:(1) Tensile properties such as dry, wet and knot tenacity and elongation of the grafted and aftertreated fibers are equal to that of original polypropylene fiber.(2) Heat shrinkage of the fibers decreases considerably by acrylic acid grafting and the fiber grafted by 62% shows heat shrinkage of 5_??_7% and does not melt till 300°C.(3) The effects of aftertreatment of the grafted fiber on the heat shrinkage are also remarkable. For example, greater heat stability is obtained by Ca-salt, NH4Cl and epoxy treatments. Melting temperature of the polypropylene monofilament is not improved by acrylic acid grafting, but elevates to as high as above 300°C by the aftertreatment with inorganic salts of some metals such as Na and Ca.(4) Tensile properties of the grafted and aftertreated fibers at elevated temperature do not improve as expected from the melting property.(5) Moisture regain of polypropylene fabric increases by acrylic acid grafting and metal salts treatments. Especially in the case of Na-salt treatment the moisture regain is about 10% in the 35.8% grafted sample.(6) It was found that the polypropylene fabric which is 20.5% grafted with acrylic acid and converted into Na-salt has excellent dyeability for cationic dye and heat settability.(7) Frictional static electricity of the acrylic acid grafted polypropylene monofilament and fabric decreases to about one half of the original polypropylenes. Conversion of the grafted acrylic acid to a hydrophilic Na-salt shows more remarkable decrease of frictional static electricity.

DRAWING OF POLY (VINYL CHLORIDE) POLYMERIZED AT LOW TEMPERATURE (PART 1)

Part. 1) Fiber were prepared from various kinds of polyvinyl chloride (PVC) polymerized at different temperature under various drawing conditions. The following results were obtained from the measurements of the density, the heat shrinkage and the X-ray difraction in these different kinds of fibers.1) The observation of the relation between the temperature and the degree of extention at break. shows the existence of the temperature range where the degree of extension at break becomes. very high. This optimum temperature range for extension coincides with the heat treating temperature range which renders the highest density And as the temperature of polymerizaion is lowerd, that optimum temperature range shifts to the higher temperature.2) Within the optimum temperature range for extention the density increases almost linearly with the degree of extention, but below this almost no density increase was observed up to the degree of extention of 400% and it begins to increase when the degree of extention exceeds 400%. At the temperature range higher than this optium temperature range the increase of the density is observed mainly before the degree of extention reaches 400% and the increase of thedensity over 400% extention was not remarkable.3) Corresponding to the variation in the density, the dimension of the crystallite determined from the X-ray study increases with the increased dgree of extention. And the degree of the increase of the dimension of crystallite is higher in the PVC polymerized at low temperature.

Experimental Studies of the Choroidal Vessels

In the present study, the actions of physical agents on the choroid will be considered as participating in surgical procedures.* The basic principle of the cure of retinal detachment involves the closure of the retinal breaks. The rational basis for this therapy was established by Gonin's 2-21 concept of direct correlation between retinal holes and retinal separation. One of the additional requirements for a successful procedure involves the approximation of the detached retina to the pigment layer and to its matrix, the choroid. 22 This can be accomplished by a reduction in volume of the scleral coat through either thermal shrinkage or mechanical shortening. A. Heat shrinkage of the sclera. Heat has been noted to reduce the volume of the scleral coat. 23 Berens and Pischell 24 and others observed clinically the shrinking of the sclera induced by electrocoagulation during surgery for retinal detachment. Scheie and Jerome 25 demonstrated experimentally

PREPARATION OF POLYVINYLCHLORIDE FIBER

The rate of strength change by drawing, cross-section change by heat drawing, and X-ray structure changes by draft, drawing and heat treatment were studied on the polyvinylchloride fiber which was prepared by wet-spinning of polyvinylchloride-Tetrahdrofuran solution.The rate of strength change shows the maximum at the 400% drawing where the heat shrinkage also shows the maximum as reported already. The cross-section changes from symmetrical bean shape to the more flat bean shape passing through a stage of unsymmetrical bean shape like letter “B”, and their skin increases. Also the structure is shown in their core part when heat drawn. No Change in degree of crystallization by draft is very low. It was observed that crystallization increases increasing draw-ratios under a constant draft, and the intensities of X-ray diffraction increase gradually on 5.38 Å and 3.87 Å. In the constant drawing, the degreeof crystallization is larger in case of higher draft fiber. By heat treatment, the degree of crystallization increases considerably and in the heat treatment under no tension, it is higher than the heat treated fiber under tension. But degree of orientation decreases in the heat treatment under no tension, and is almost the same as in the original fiber under the heat treatment with tention.