Nucleation of the γ-form in isotactic polypropylene (PP) under high pressure was investigated. Three nucleating agents were used to nucleate crystallization of PP under atmospheric pressure: commercial Hyperform HPN-20E from Milliken Chemical, poly(tetrafluoroethylene) particles nucleating the α-form, and calcium pimelate nucleating the β-form. Crystallization of neat PP and PP with addition of 0.2 wt% of the nucleating agents was studied. Specimens were either kept at 200 °C under pressure of 200 MPa for time ranging from 2 min to 4 h or for 15 min under pressure ranging from 1.3 to 300 MPa. After cooling to ambient temperature and releasing the pressure, the specimens were analyzed by DSC, WAXD, and PLM to have an insight into the structure and to determine a crystallinity level and contents of crystallographic forms. Both α-nucleating agents strongly nucleated crystallization of PP under high pressure in the γ-form, whereas the β-nucleating agent had only a slight effect. The results show the possibility to use nucleating agents to nucleate the γ-form of PP under high pressure.

In polymer processing, crystallization generally occurs in complex, inhomogeneous and coupled mechanical (flow, pressure), thermal (cooling rate, temperature gradient) and geometrical (surface of processing tools) conditions. A first route to understand crystallization in processing conditions is to design model experiments to isolate the specific influence of a given parameter. The emphasis will be laid here on the influence of: (i) shear flow through rheo-optical measurements using the commercial RheoScope module, (ii) high cooling rates obtained with the modified hot stage Cristaspeed (up to 2 000 °C min⁻¹) and (iii) high pressures in the original Cristapress cell (up to 200 MPa). Numerical simulation is also a useful tool to understand and predict the coupled phenomena involved in crystallization. Based on Avrami's ideas and equations, a general differential formulation of overall crystallization kinetics has been proposed by Haudin and Chenot (2004). It is able to treat both isothermal and non-isothermal cases, and has been extended to crystallization in a limited volume without and with surface nucleation inducing transcrystallinity.

1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS) is highly effective in nucleation of the α- form of isotactic polypropylene (iPP). However, its role in high-pressure crystallization of iPP, facilitating the formation of the γ- polymorph, has not been explored. The present paper focuses on the influence of DMDBS on nucleation of high-pressure crystallization of iPP. iPP with 0.2–1.0 wt.% of the DMDBS was crystallized under elevated pressure, up to 300 MPa, in various thermal conditions, and then analyzed by PLM, WAXD, SEM, and DSC. During cooling, crystallization temperatures (T_c) were determined. It was found that under high-pressure DMDBS nucleated crystallization of iPP in the orthorhombic γ- form. As a consequence, T_c and the γ- form content increased for the nucleated iPP, while the size of polycrystalline aggregates decreased, although the effects depended on DMDBS content. The significant increase of T_c and the decrease of grain size under high pressure of 200–300 MPa required higher content of DMDBS than the nucleation of the α-form under lower pressure, possibly due to the effect of pressure on crystallization of DMDBS itself, which is a prerequisite for its nucleating activity.

The purpose of the paper is to study the influence of molecular architecture of poly(ethylene terephthalate) (PET) on its ability to be processed by stretch-blow molding, which is not well documented in the literature. To evaluate this process ability, it proposes an original strategy combining laboratory analyses and experiments on a prototype machine. PET copolymers were prepared from three types of comonomers: diethylene glycol (DEG), isophthalic acid (IPA) and trimethylolpropane (TMP). It is first shown, through laboratory experiments, that the nature of the polymer in terms of chain constitution (copolymerization), chain length (intrinsic viscosity) and purity (catalytic residues) greatly affects many properties: melt crystallization, thermal properties, polymer rigidity and drawability. These different properties obviously induce very different behaviours at the different steps of the stretch-blow molding process: injection-molding of the preform (quenchability), heating (IR absorption), stretch-blow (rigidity and drawability). The stretch-blow step has been simulated on a prototype apparatus designed in our laboratory. It has been shown that free blowing can be used to characterize the process ability of the polymer. A statistical analysis has confirmed the great differences between the materials investigated and pointed out the complexity of the material response during blowing.

The crystallization of 3 polyamides 66 has been studied by optical microscopy and differential scanning calorimetry (DSC). Nonisothermal crystallization kinetics has been analyzed using Ozawa's equation. Two polymers have close behaviors with a crystallization mainly spherulitic. The third one, which has the highest molar mass, is subject to intense transcrystallinity, which disturbs the crystallization kinetics (shoulder on the DSC curves and low Avrami exponent). For this polymer, original methods based on a detailed analysis of transcrystallinity have been applied to measure crystal growth rate and to determine the “intrinsic” crystallization kinetics, that is, not polluted by transcrystallinity.