Polymer Crystallization

Microfluidic shear can induce the coil-to-rod transition and interchain π-π stacking of the rods of poly(3-hexylthiophene) (P3HT) in toluene. It is verified that shear-induced π-π stacked rods are mesomorphic, namely, flow-induced precursors (FIPs). Shear temperature is an important parameter for determining the amount of FIP. The amount of FIP dramatically affects the crystallization kinetics, dispersion, amount, and intrachain ordering of P3HT nanofiber when P3HT is isothermally crystallized at 12°C in toluene.

Using the phase field method to reproduce the crystallization of a polymer leads to prediction of the microstructure. This approach allows the study of temperature and temperature rate influence on the final microstructure and helps to predict the mechanical properties of the polymer, which is an industrial goal for polymer manufacturing.

The crystallization behavior of diblock copolymers instigated from microphase separated melt is explored by dynamic Monte Carlo simulation. Dynamic Monte Carlo simulation is one of the potential tools of use to study the phase transition of a polymer. The influence of thermal history determines the final crystal morphology of the diblock copolymers. Thermal annealing endorses coalescence of melt microdomains with more relaxed structures, which remain intact after nonisothermal crystallization. In contrast, microphase separated melt without annealing offers morphological perturbation during nonisothermal crystallization. The rate of crystallization of microphase separated annealed melt is much faster than microphase separated melt without annealing due to the more relaxed structure of microphase separated melt achieved through the process of annealing.

Polylactide (PLA) with different crosslinking densities or average molecular weights between the crosslinking points was fabricated by reactive extrusion, aiming to improve the heat deflection temperature (HDT) of this material. The crosslinked PLA showed increased crystallization rate but unchanged glass transition temperature. The theoretical calculation indicated that the average molecular weight between the crosslinking points is not enough to influence the chain segment movement of PLA.

The authors propose an investigation of tensile properties of new commercially available poly(ether ketone ketone) copolymers (Arkema). By modifying terephthaloyl and isophthaloyl isomer ratios and crystallization conditions, a large range of crystallinity is attainable experimentally. As a result, the authors highlight a master curve describing crystallinity and tensile properties such as modulus and yield stress.

Random copolymers of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) can show particular morphologies of crystals formed in the near-surface region during annealing from an amorphous phase. The morphologies reflect the composition and randomness of the copolymer, and the constraint on the crystallizing region caused by the restricted thickness in thin films.

The polybutylene terephthalate (PBT) filament had a high instantaneous elastic recovery and aging of the POY PBT yarn had no effect on the instantaneous elastic recovery of the PBT filament. The effect of first heater temperature on PBT false-twist textured yarn showed that with increasing first heater temperature, the tensile and crimp properties of textured yarn were improved. Some fluctuation in the physical properties of texturized yarns was observed during the aging (80 days), but it was within the allowed range.

The incorporated biocompatible EBH nucleating agent (NA) not only increased the crystallization temperature and crystallization rate and improved the mechanical property of the poly(ε-caprolactone) (PCL), but also enhanced the thermal degradation temperature of the PCL. It can likely be attributed to good interfacial adhesion between the PCL and EBH, and the excellent flame retardant effect of the EBH on the PCL.

The relation between crystallization peak temperature and cooling rate from the melt reveals that the observed crystallization temperatures of polypropylene (PP)/poly(4-methyl-1-pentene) (PMP) blends are in good agreement with their homopolymers. PMP does not affect the crystallization temperature of thermodynamical stable α-form of PP under the nonisothermic condition and vice versa. However, PMP tends to prevent the formation of conformational disordered phase at cooling rates ranging from 50 to 100 K s⁻¹.

Composites of polylactic acid (PLA) and high loading carbon nanotube (CNT) fibers are produced by a facile method: polymer solution infiltration and subsequent drying. Easy wetting and infiltration of PLA into porous CNT fiber networks generate good impregnation and PLA/fiber interfaces. This good adhesion leads to the formation a of transcrystalline layer of PLA on the fiber surface, resulting in increased thermal stability, faster nucleation, and higher crystallinity.

Compound β-nucleating agents can self-assemble into oriented uniform and fine needle-like frameworks in polypropylene cast films. After biaxial stretching of the cast films containing oriented β-transcrystals, microporous membranes with more uniform micropore distribution were obtained. This work provides a new understanding of the relationship between nucleating agent framework size uniformity, crystallization uniformity, and micropore uniformity.

A large number of processing aids that are used in the formulation of polyolefins consist of hydrocarbon derivatives such as oils and waxes. The main difficulties associated with those blends are the low viscosity ratio between the additive and the polymer resin in the molten state as well as the potential phase separation in the solid state. The aim of this article is therefore to investigate the miscibility and morphology developments occurring during the processing and solidification of PP and HDPE in the presence of a low molar mass PE oligomer.

Graphene is beneficial in enhancing the mechanical properties of PVDF at low temperatures. The compatibility of PVDF/graphene composites decreases with temperature during deformation. The transformation of PVDF from an α-crystal to a β-crystal is suppressed with temperature increasing during uniaxial tensile deformation. The stress-induced lamellar fragments recrystallize into an α-crystal after yield. The newly formed α-crystal orients with the loading stress. The exceeded stress induces the conversion from the newly formed α-crystal to a β-crystal.

Although poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) is highly flexible and biodegradable with wide application potential, its crystallization during molding is quite slow, which restricts its practical applications. The relationship between the residual crystal amount and subsequent crystallization was observed in real time by online near-infrared and it was found that the residual crystal amount was very importance for subsequent crystallization of PHBH under dynamic conditions such as practical extrusion molding.

Toward a better understanding of natural rubber properties, new polyisoprene/lipid hybrid materials were synthesized. The study of their thermal properties allowed new insights into the cold crystallization of natural rubber. It was thus demonstrated that the free lipids existing on the natural polymer were crystallization enhancers while the ones linked to the polymer backbone were crystallization inhibitors.

The room temperature stretching of pre-oriented PLA film can only increase rigid amorphous fraction (RAF) transformation to mesophase rather than to highly perfect crystals.

The processing approach of ultrasonication of the PVDF solution followed by vacuum drying of the cast films produces an excellent crystallization pattern of lamellar nanostructures resulting in polar γ phase with improved optical transparency, mechanical and electrical properties (PVDF-US-VD). Similar crystallization patterns are also exhibited when optimally FSWCNTs are introduced in PVDF where further improvements in optical, electrical, and mechanical properties are observed.