Effects of processing on the microstructure, melting behavior, and equilibrium melting temperature of polypropylene

Abstract

SYNOPSISPolypropylene (PP) was extruded and injection-molded several times to mimic the effect of recycling procedures on PP. Differential scanning calorimetry (DSC) was used to follow crystallization rates under isothermal conditions in a temperature range of 120-130°C. Melting behavior and equilibrium melting temperatures were studied using the HoffmanWeeks method of extrapolation. Optical microscopy combined with a hot stage was also used to follow the spherulite microstructure and crystal phase upon recycling of PP. Wideangle X-ray spectroscopy identified the crystal phase a t different isothermal crystallization temperatures. Twin melting peaks obtained for PP melting following isothermal crystallization were associated with crystal rearrangement during fusion. PP spherulite size and equilibrium melting temperatures were seen to increase with processing events, whereas reprocessing decreased nuclei density. 0 1996 John Wiley & Sons, Inc.

Highly efficient nucleating additive for isotactic polypropylene studied by differential scanning calorimetry

“…They are commonly used in the polymer industry to shorten injection‐molding cycle times, thus reducing production costs, generating smaller spherulites, and thus improving the optical and mechanical properties, as is the case for iPP 11. A large number of compounds were reported to nucleate the α form of iPP,10–14 and several others act as nucleating agents of the β form,15–27 depending on the dispersion and concentration of the additives and the cooling rates.…”

Effects of reprocessing on the structure and mechanical properties of poly(trimethylene terephthalate)

“…Studies on the nature of the degradation caused by reprocessing and its effects on the properties of polymers have been conducted for a large number of polymers, including polyethylene,2 polypropylene,3–5 polycarbonate,6–8 poly(ethylene terephthalate) (PET),9–13 poly(butylene terephthalate) (PBT),14 nylon‐6,15 poly(ether imide),16 poly(ether ether ketone),17 and liquid‐crystalline polymers 18, 19…”

Differential scanning calorimetry of copolymer of isotactic polypropylene backbone with grafted poly(ethylene‐co‐propylene) branches

“…In isothermal crystallization experiments, multiple melting peaks are produced after crystallization at a low T c , but not at a high T c 35–37. Similarly, in nonisothermal crystallization experiments, many researchers have found multiple melting peaks after fast cooling (low T c ), but only one melting peak after slow cooling (high T c ) 33, 37–40.…”