Antinucleating action of polystyrene on the isothermal cold crystallization of poly(ethylene terephthalate)

Abstract

The effect of polystyrene (PS) on the kinetics of the cold crystallization of poly(ethylene terephthalate) (PET) was thoroughly investigated. The PET/PS blends were essentially immiscible, as observed by dynamic mechanical thermal analysis, which showed two distinct glass-transition temperatures, and by scanning electron microscopy. The neat PET and its blends were isothermally cold-crystallized at various temperatures, and the kinetic parameters were determined with the Avrami approach. PET and its blends presented values of the Avrami exponent close to 2, and the kinetic constant increased with the crystallization temperature increasing. For all the crystallization temperatures studied, the presence of only 1 wt % PS significantly reduced the rate of cold crystallization of PET. A further increase in the PS concentration did not show any significant influence. The blends presented higher values of the activation energy for cold crystallization, which was estimated from Arrhenius plots. The equilibrium melting temperature of neat PET was determined on the basis of the linear HoffmanWeeks extrapolative method to be $ 255 C. This value decreased in the presence of PS, and this suggested limited solubility between PET and PS. From the spherulitic growth equation proposed by Hoffman and Lauritzen, the nucleation parameter was obtained, and it was shown to be higher for the neat PET than for the blends. Moreover, a transition of regimes (I ! II) was observed in both PET and its blends. From the investigations conducted here, it is clear that PS in small amounts causes a reduction in the rate of PET crystallization, acting as an antinucleating agent.

Effect of polystyrene on poly(ethylene terephthalate) crystallization

“…It should be noted that, under the tests conditions PS is a completely amorphous polymer, immiscible in PET; the solubility limit of PS in PET is believed to be less than 1%, thus it is possible that once the solubility limit between PET and PS to be reached PS is segregated at amorphous zone then producing little effect on the crystalline phase of PET. In literature database several explanations are presented for the multiple crystallization phenomenon: two kinds of amorphous regions, inter-lamellar and inter-spherulite, different crystalline geometries, co-crystallization and fractional crystallization, secondary or recrystallization effects 6,9,11,12,14,28,[30][31]35,[41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] . PET crystallization in PET/PS blends proceeds at a higher temperature and lower crystallization rate than in the neat resin.…”

“…Although heating and cooling rates during industrial processing are very high and the material is subjected to severe dynamical stresses, differential scanning calorimetry (DSC) static tests, carried under far milder conditions, may be used as a guide to select the processing methods. Moreover, precise determination of optimal melting parameters is needed to avoid polymer degradation during processing and excessive energy consumption [12][13][14] . According to packing industry cold crystallized preforms are a serious waste of money; thus, the solution to this problem would be very welcome.…”

“…From previous work we know that blending a small amount of an amorphous polymer may hinder unwelcomed cold crystallization of PET and prevent excessive crystallinity under processing conditions. Thus, polystyrene, an apolar amorphous polymer appears to be a good candidate 12,[15][16][17][18][19][20][21] . The present work is concerned with an investigation of the melting and nonisothermal cold crystallization of PET and PET/PS blends with 1 to 60% of PS content.…”

Controlling sandwich‐structure of PET microcellular foams using coupling of CO2 diffusion and induced crystallization

“…49,[54][55][56] The Avrami equation is in the form as 49,[54][55][56] The Avrami equation is in the form as…”

Melting and crystallization of poly(3-hydroxybutyrate): effect of heating/cooling rates on phase transformation

“…Macroscopic crystallization in polymers starts at very low rates due to the first, slow nucleation step; crystallization rate increases during the main or bulk crystallization and then decreases as the material is depleted of crystallizable molecules and due to spherulitic impingement [20][21][22] . Most crystallization parameters are strongly dependent on the cooling/reheating rate, and the dependence is different for the melt and cold crystallization processes.…”