Crystallinity polyethylene, effect

Elenga, R., Seguela, R. and Rietsch, F., Thermal and mechanical behaviour of crystalline polyethylene terephthalate) effects of high temperature annealing and tensile drawing, Polymer, 32, 11, 1975-1981 (1991). 

As symmetrical molecules approach within a critical distance during melt processing, crystals begin to form in the areas where they are the most densely packed. A crystallized area is stiffer and stronger, a non-crystallized (amorphous) area is tougher and more flexible. With increased crystallinity, other effects occur. As an example, with polyethylene (crystalline) there is increased resistance to creep. 

Polyethylene. The effect of crystallinity on the diffusion coefficient of iso-octane at 54°C in PE was determined in a sorption experiment. Films of Sclair PE (DuPont Chemical Co., Kingston, Ontario) were compression-molded in a hot platens press at 170°C and were allowed to cool in the press. All films were 200 /xm thick. The properties of the resins are given in Table II. 

PETAN-56, Curing Kinetics of an Epoxy Adhesive Using Isothermal DSC Kinetics. PETAN-58, Polyethylene The Effect of Thermal Conditioning on Percent Crystallinity. 

COM Compan, V., Del Castillo, L.F., Hernandez, S.I., Lopez-Gonzalez, M.M., and Riande, E., On the crystallinity effect on the gas sorption in semicrystalline linear low density polyethylene (LLDPE), J. Polym. Sci. Part B Polym. Phys., 45, 1798, 2007. 

Sakurai T, Nagakura H, Gondo S, Nojima S. Crystallization of poly(e-caprolactone) blocks confined in crystallized lamellar morphology of poly(c-caprolactone)-Wock-polyethylene copolymers effects of polyethylene crystallinity and confinement size. Polym J 2013 45 436-443. 

From a brief consideration of the properties of the above three polymers it will be realised that there are substantial differences between the crystallisation of simple molecules such as water and copper sulphate and of polymers such as polyethylene. The lack of rigidity, for example, of polyethylene indicates a much lower degree of crystallinity than in the simple molecules. In spite of this the presence of crystalline regions in a polymer has large effects on such properties as density, stiffness and clarity. 

This effect is also observed with some polymers. The trans form of a hydrocarbon chain requires an energy about 0.8 kcal/mole less than the gauche. The trans form leads to an extended molecule and in hydrocarbons this becomes more favoured as the temperature is lowered. Linear polyethylenes take up this conformation in the crystalline state. 

The type of counterion present in an ionomer may, or may not, have a significant effect of properties. For polyethylene-based ionomers, where the presence of crystallinity has an appreciable effect on properties, the type of counterion present does not appear to have a significant effect on either modulus or tensile strength, as Fig. 4 indicates. However, in amorphous ionomers, the effects of changing the counterion from a monovalent one, as in Na or K, to a divalent one, such as Ca, may be appreciable. 

The effect of incorporating p-hydroxybenzoic acid (I) into the structures of various unsaturated polyesters synthesised from polyethylene terephthalate (PET) waste depolymerised by glycolysis at three different diethylene glycol (DEG) ratios with Mn acetate as transesterification catalyst, was studied. Copolyesters of PET modified using various I mole ratios showed excellent mechanical and chemical properties because of their liquid crystalline behaviour. The oligoesters obtained from the twelve modified unsaturated polyesters (MUP) were reacted with I and maleic anhydride, with variation of the I ratio with a view to determining the effect on mechanical... 

The Tg of P-plastomers changes as a function of ethylene content. The Tg decreases with increasing ethylene content, primarily due to an increase in chain flexibility and loss of pendant methyl residues due to incorporation of ethylene units in the backbone. It is well known that PP has a Tg of 0°C, and polyethylene a Tg< —65°C. The addition of ethylene to a propylene polymer would therefore be expected to decrease the Tg, as is observed here. A secondary effect would be the reduction in the level of crystallinity associated with increasing ethylene content, which is expected to reduce the constraints placed upon the amorphous regions in proximity to the crystallites. Thus, an increase in ethylene content will result in a lower T as well as an increase in magnitude and a decrease in breadth of the glass transition. 

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