Necking, polypropylene

Ny lon-6 (108 g) carpet backed with calcium-carbonate-filled latex and polypropylene was charged to a 1000-mL three-neck round-bottom flask (equipped with a condenser) with 6 mL of 85% phosphoric acid. Superheated steam was injected continuously during a 45-min period. The vapor temperature of the reaction medium was 250-300°C. The volume of distillate collected was 1065 mL. The distillate contained 1.9% e-caprolactam (as determined by GC), which corresponded to a crude yield of 37.5%. The distillate was fractionated in a distillation column and the nonaqueous phase removed. The remaining aqueous phase was treated with 2% potassium permanganate at 40-50°C for 2 h. Evaporation of... 

Voids within a sample are a major cause of internal haze. We see the effect of voiding when we stretch polymers, such as high density polyethylene and isotactic polypropylene, that have distinct yield points and clearly defined necks (as discussed earlier in this chapter). The... 

A 3000 molecular weight polypropylene ether) triol (Arcol F3020, 90 g) was mixed with maleic anhydride (60 g) and zinc chloride (2.25 g) in a three-necked round-bottomed flask equipped with a magnetic stirrer, a condensor and a thermometer. Under a nitrogen atmosphere, the reaction mixture was heated to 190 °C... 

In a 250-ml three-necked flask, polypropylene glycol (0.02 mol) and 2,4-toluene diisocyanate (0.042 mol) were added and reacted under conditions provided in Table 1. When the reaction was completed, all products were isolated as transparent colorless liquids. 

Retarded Necking in Continuous Nylon-Fiber Reinforced Polypropylene... 

The tensile properties of isotactic polypropylene materials reinforced with continuous nylon fibers were measured. Less than 10 vol % of the fibers leads to an increased yield strength and yield elongation. As little as 3 vol % of the nylon fibers increased the elongation at necking from 10 to 20%. This retarded necking arises from the fiber-matrix debonding which delocalizes the microscopic yielding processes. 

Thus, reinforcement of polypropylene with as little as 3 vol % of nylon fibers increases the elongation at which necking and stress whitening occur from 10% for the unreinforced matrix to 20% for the composite. We call this phenomenon "retarded necking. ... 

For small samples, it is recommended that polypropylene [e.g. Nalgene ] bottles be used with a cap insert inside the neck. This type of plastic packaging is extremely resilient to compression and damage. Glass bottles should be avoided where possible. All very small quantities should be shipped as a combination package - an inner package in a UN approved box containng a suitable fabric adsorbent... 

Holding adequate retention samples can also be part of control. An example is where a plastic bottle is put under test with a product. On removal of the polypropylene cap a yellow discolouration is found on the bottle neck. The questions asked can be is it product-related Is it a reaction between cap and bottle Could it happen on an uncapped bottle (probably unlikely) This situation could be resolved by testing bottles capped without product, together with separately stored retention samples of caps and bottles. How retention samples are stored and what they are stored in, etc., are additional questions which have to be asked. 

Shrink sleeving made from lay flat tubing or welded tubing is widely used as a tamperevident overwrap to enclose either a whole container or neck and closure. Materials include PVC, polypropylene and polyester. Shrink sleeving can improve container barrier properties or light exclusion. 

The ASTM procednre notes that tensile strength and elongation at break values for unreinforced polypropylene are generally highly variable dne to inconsistencies in necking or drawing of the center section of the test specimen. Therefore, the... 

The clear separation of transformation from spherulitic to fibrous structure and the drawing of fibrous structure observed with nylon 6 are not found with polyethylene or polypropylene. This could lead to the conclusion that in these polymers the deformational process is basically different from that in nylon 6. But, closer inspection of material drawn to gradually increasing draw ratios reveals a closer similarity than one can derive from load-elongation curves and direct observation of necking. 

A spout cap is a dropping mechanism on top of the neck of the bottle. The most frequently used spout cap is the Zentrop dropper. This consists of a chlorobutyl mbber dropper mounted in a polypropylene screw cap and closed with a small polypropylene cap. In case of incompatibility of the liquid with the chlorobutyl rubber a Zentrop cap with a pol5q)ropylene dropper can be used. 

In 1981, Bernstein and Zapas [10] extended the work of Ericksen [11] (which describes the discontinuous deformations of solid elastic bars) to viscoelastic materials which obey the Bernstein, Kearsley, and Zapas (BKZ) theory [12]. As in the case of Ericksen s work, the Bernstein and Zapas treatment cannot predict a priori when the material will exhibit the phenomenon of necking, but it does give an explanation for the formation of the neck, which depends on the stretch history. Most recently we have obtained experimental data, using a variety of stress and strain histories, on isotactic polypropylene, the mechanical behavior of which can be described fairly well by the BKZ theory [13]. In most cases the experiments were carried out up to and beyond the point of necking until fracture occurred. In what follows we present these results and also some results obtained on several different linear polyethylenes. 

Log creep strain versus log time for specimens of polypropylene under a constant applied tensile load. The letter n indicates the strain at which necking occurred and e the elongation at which the neck had propagated through the entire specimen. The arrows indicate fracture. 

Marion L. Hodgdon and I are preparing for publication results of a numerical study we have made of equations of the form (3.36) using functions T that appear appropriate for such melt-spun fibers as nylon and polypropylene. Our report of that study will contain examples of cases in which the assumption that the homotopy t X j ( ) describes neck formation in the interval [t, t" ] implies that t(t) increases with t in this interval. 

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