Annealing of commercial block polypropylene. I. Thermal and physical properties

Abstract

SYNOPSISInvestigations were carried out regarding the effect of annealing of ethylene-propylene block copolymer (block PP) moldings on their tensile impact strength (TIS) , brittle temperature (Tb) , and other mechanical properties. Annealing near the melting point improves TIS and Tb as the result of recrystallization. With a system in which a minute amount of talc is added as a nucleating agent, the degree of improving TIS through annealing is considerably less than that with a nonnucleated system. The effect of annealing on the impact strength is due to changes of fine texture and morphology of crystallites and is explicable by recrystallization and polymer diffusion. 0 1992 John Wiley & Sons, Inc. INTRO DU CTlO NPolypropylene ( PP ) has various excellent properties as a general purpose resin, such as thermal resistance, rigidity, and chemical resistance. However, its greatest disadvantages are its low impact strength and high Tb temperature, which can be improved by copolymerization with another olefin (generally with ethylene) or blending with an elastomer, with inevitably decreasing the high rigidity characteristics of PP.We have already proposed that annealing of PP blends after their molding is effective as a means of improving impact strength and Tb without sacrificing rigidity.'v2 There have also been reported some similar ~t u d i e s .~.~ Commercial block polypropylenes have been produced through the first-stage polymerization to give a homo-PP or a random copolymer of propylene with a small amount of ethylene, followed by the second stage to effect copolymerization of propylene and ethylene. In some cases, a small amount of polyethylene (PE) has been produced in the second-stage polymerization. Accordingly, a block PP can be regarded as a highly complicated composite of polypropylene, poly (ethylene-co-propylene) ( P E P ) , and p~lyethylene.~-~ * To whom correspondence should be addressed. In the present report, in the same way as with the study on PP blends, we studied the annealing effect on several commercial block PPs regarding mechanical properties and morphology. EXPERIMENTALAll polymers used were block PPs produced by Tokuyama Soda Co., among which block PP-A and PP-B were of commercial grade and PP-C was a special sample of high ethylene content prepared under similar condition. Table I shows compositions and properties of the polymers, of which characterizations were conducted in the same manner as in the previous report' in accordance with ASTM-D1822 and ASTM-D746. The values of TIS in Table I indicate the average of 10 measurements ( n = 10). The standard deviations of TIS values were less than 10% of the average values. The values of Tb were determined by the statistical law with the data measured at least at five different temperatures. Other values in Table I were the average of the data measured with five test specimens. Measurement of isothermal crystallization velocity was made by a differential scanning calorimeter ( Perkin-Elmer Co., Model DSC-lB), by first melting the sample i...

The functions of crystallizable ethylene‐propylene copolymers in the formation of multiple phase morphology of high impact polypropylene

“…2,3,9,[13][14][15] It is generally believed that the dispersed phase in hiPP exhibits a core-shell structure with PE core and EPR shell. [16][17][18][19] This coreshell structure has proven to be efficient for the toughness-rigidity balance of the material. However, the understanding of the phase morphology of hiPP is far from perfect.…”

“…However, the understanding of the phase morphology of hiPP is far from perfect. Although one can obtain some information about the phase structure of hiPP bulk with the help of cryoultramicrotomy, staining, and surface etching techniques, 2,3,5,9,[13][14][15][16][17][18][19] it is very difficult to gain the structural details of the phase morphology of the material. The corresponding relationship between the complicated chain structure and phase morphology has not been completely established.…”

Isothermal crystallization behavior and properties of polypropylene/EPR blends nucleated with sodium benzoate

“…1 However, its great disadvantage is poor impact strength at low temperature. [2][3][4] One method to solve this problem is to blend iPP with a rubber, such as ethylene-propylene rubber (EPR) or ethylene-propylenediene terpolymer (EPDM).…”

Annealing in Low Density Polyethylene at Several Temperatures

“…There is a vast literature that uses different techniques to study annealing for semicrystalline polymers, [10][11][12] but undoubtly the main approach is DSC. For amorphous and crystalline phases rearrangements, the importance of annealing is that such experiments can detect the partial melting followed by recrystallization [13][14][15] as well as the phenomenum of isothermal thickenning.…”

“…For amorphous and crystalline phases rearrangements, the importance of annealing is that such experiments can detect the partial melting followed by recrystallization [13][14][15] as well as the phenomenum of isothermal thickenning. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The evident difference between the isothermal crystallization and the annealing experiment is the initial state of the processes. In the former case the system is almost totally amorphous at the beginning, whereas in the latter the crystallization starts from a semicrystalline condition.…”