Necking polymers

Figure 14.7 Considere construction for tensile strain. The maximum and minimum values of a in Figure 14.6 are given by the tangents to the curve of true stress ct, from 8 = -1. Polymer A forms an unstable neck polymers Bj and B2 form stable necks.

Vemebler, Nebelgerat neck Hals micros Tubustrager necking polym Halsbildung,... 

With the expiry of the basic ICI patents on poly(ethylene terephthalate) there was considerable development in terephthalate polymers in the early 1970s. More than a dozen companies introduced poly(butylene terephthalate) as an engineering plastics material whilst a polyether-ester thermoplastic rubber was introduced by Du Pont as Hytrel. Polyfethylene terephthalate) was also the basis of the glass-filled engineering polymer (Rynite) introduced by Du Pont in the late 1970s. Towards the end of the 1970s poly(ethylene terephthalate) was used for the manufacture of biaxially oriented bottles for beer, colas and other carbonated drinks, and this application has since become of major importance. Similar processes are now used for making wide-neck Jars. 

This section deals with the procedure used by American Polymer Standards Corp. in the manufacture of GPC/SEC gels. The reaction is performed in a three-neck flask equipped with a reflux condenser, a mechanical stirrer, and a thermometer. First, prepare the water phase and then the organic phase. After mixing the organic phase into the water phase, stir at 300 to 400 rpm for 2 hr at 40°C. Heat to 70°C and continue mixing at 150 rpm for 10 hr. Cool to room temperature, (RT), dilute with water, and filter. Wash the gel with water, acetone, toluene, and again with acetone. Dry at 70°C for 12 hr, classify the gel, and package. 

In a 5 liter three-necked flask, fitted with a reflux condenser, agitator and thermometer, were placed 1,393 g (9.41 mols) of redistilled (CH3)2Si(OEt)2 and 1,1 lOg (9.41 mols) of (CH3)3SiOEt. To this solution was added 254 g (14.11 mols) of water containing 7.5 g of NaOH (approximately 1 NaOH per 100 silicon atoms). This insured the formation of only straight chain polymers. The mixture was heated to 40°C and the temperature continued to rise for nearly an hour. After adding 50 cc (20% excess) more water, the mixture was refluxed for two hours and then allowed to stand overnight. 

A. Polymeric Benzylamine [Benzene, diethenyl-, polymer with elhenyl-henzene, aminomethylated]. In a 300-ml., one-necked, round-bottomed flask equipped with a reflux condenser and a magnetic stirrer are placed... 

B. Polymeric Urea [Benzene, diethenyl-, polymer with ethenylbenzene, [[[[(1 methylethyl)amino]carbonyt]amino]methyl] deriv.] A 10.0-g. portion of benzylamine polymer beads prepared as in Part A and 125 ml. of tetrahydrofuran (Note 6) are combined in a 300-ml., three-necked, round-bottomed flask equipped with a magnetic stirrer, a dropping funnel, and a condenser fitted with a gas-inlet tube A nitrogen atmosphere is established in the system, and the slurry is stirred while 1.35 g. (0.0159 mole) of isopropyl isocyanate [Propane, 2-isocyanato-] is added. This causes an exothermic reaction, which subsides after about 20 minutes. The mixture is then stirred at room temperature for 22 hours and at reflux for an additional 4 hours. The beads are collected by filtration, washed with 150-ml. portions of tetrahydrofuran (Note 6) and methanol, and dried under reduced pressure over calcium chloride to yield 9.09 g, of the isopropyl urea polymer. 

The transition into the oriented state is accompanied by the formation of a neck , a sharp and abrupt local constriction of the sample, in which the extent of orientation and the degree of extension are mudh higher than in the rest of the polymer. After the neck has been formed, further orientation of the sample occurs by spreading of the neck to the entire length of the polymer. When the sample is extended after passing into the oriented state, it undergoes further deformation and at some critical extension it breaks. 

Necking occurred in samples of polymer E and of the thermoplastic Phenoxy. The other, more crosslinked polymers failed before necking started. The results on the post yield behavior are included in Table 2.1. Apparently, a process such... 

Polymer A with GIC = 160 J m-2 is typical for thermoset materials which are expected to be brittle [78]. At the other end of the series, polymer E and Phenoxy with G,c > 1 kJ m 2 are tougher than several wellknown thermoplastics (PMM A, PS, PES). In contrast to the more crosslinked polymers, polymer E and Phenoxy PKHJ show necking after yielding in tensile tests with draw ratios A = 1.7 and A = 2.1, respectively (Table 2.1). 

Usually, the molecular strands are coiled in the glassy polymer. They become stretched when a crack arrives and starts to build up the deformation zone. Presumably, strain softened polymer molecules from the bulk material are drawn into the deformation zone. This microscopic surface drawing mechanism may be considered to be analogous to that observed in lateral craze growth or in necking of thermoplastics. Chan, Donald and Kramer [87] observed by transmission electron microscopy how polymer chains were drawn into the fibrils at the craze-matrix-interface in PS films [92]. One explanation, the hypothesis of devitrification by Gent and Thomas [89] was set forth as early as 1972. 

An uniaxial mechanical deformation provokes drastic changes in the identation pattern of drawn polymers. Some typical results illustrating the dependence of MH on draw ratio for plastically deformed PE are shown in Fig. 19 a. The quoted experiments 12) refer to a linear PE sample (Mw 80.000) prepared in the usual dumbbell form drawn at a rate of 0.5 cm/min at atmospheric pressure. Identations were performed longitudinally along the orientation axis. Before the neck (A = 1), the... 

To a 50-mL three-necked flask (Fig. 3.18b) equipped with a stirrer (comprised of a stainless steel shaft and paddle), a head for the distillation of water, and a nitrogen inlet is added 20 g of purified 11-aminoundecanoic acid. The flask is then purged with nitrogen for 5 min. The flask is warmed in a silicon oil bath to 220° C and maintained at this temperature for 10 h. After raising the stirrer from the molten mass, the reaction is cooled under nitrogen and the resultant polymer removed by breaking the glass. The Tm of the polymer is 185—190° C and the rjmh in m-cresol (0.5% at 35°C) is 0.6—0.7. 

To a 50-mL straight-wall three-necked flask (Fig. 3.18b) equipped with a magnetic stirrer, nitrogen inlet/outlet, and condenser unit in a heating block are added 11.29 g of nylon salt and 0.093 g of hexamethylene diamine (2 mol % excess). This mixture is reacted for 2 h at 210° C and 3 h at 270°C. The resultant polymer is colorless and transparent and has a r/rei of 2.54 (1% solution in m-cresol, 25°C). 

Thermoplastic polymers subjected to a continuous stress above the yield point experience the phenomenon of cold-drawing. At the yield point, the polymer forms a neck at a particular zone of the specimen. As the polymer is elongated further, so this neck region grows, as illustrated in Figure 7.7. 

Amorphous polymers may be cold drawn only below their glass transition temperatures above this temperature, they stretch but without forming a well-defined neck region. Crystalline polymers, by contrast, can be cold drawn at all temperatures up to almost their melting points. 

The synthetic approach is very simple and does not require any special set up. In a typical room temperature reaction, 1.0 mL aqueous solution of cadmium chloride was added to 20 mL aqueous solution of soluble starch in a 50 mL one-necked round-bottom flask with constant stirring at room temperature. The pH of the solution was adjusted from 6 to 11 using 0.1 M ammonia solution. This was followed by a slow addition of 1.0 mL colourless selenide ion stock solution. The mixture was further stirred for 2 h and aged for 18 h. The resultant solution was filtered and extracted with acetone to obtain a red precipitate of CdSe nanoaprticles. The precipitate was washed several times and dried at room temperature to give a material which readily dispersed in water. The same procedure was repeated for the synthesis of PVA and PVP - capped CdSe nanoparticles by replacing the starch solution with the PVA and PVP polymers while the synthesis of elongated nanoparticles was achieved by changing the Cd Se precursor ratio from 1 1 to 1 2. The synthesis of polymer capped ZnSe nanoparticles also follows the same procedure except that ZnCb solution was used instead of CdCb solution. 

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