Polymer Crystallization

Enhanced elastic behavior of iPP is conferred by the addition of small contents of propylene 1-Hexene copolymer. Highly interconnected lamellae from homogeneous melts of iPP/PH11 blends undergo more effective stress transfer, and monoclinic to mesophase transformation during deformation, than lamellae formed from phase separated melts of iPP/PH21 blends.

A series of chitosan-based supramolecular comb-like polymers containing long alkyl side chains were prepared via non-covalent bonds. All these comb-like polymers aggregate into a layered structure. The side-chain packing structure of these comb-like polymers depends on the side chain length. Both the steric hindrance and the tendency of side-chain aggregation affect the packing state of alkyl side chains together.

In iPP/glass fiber composites, the orientation of isotactic polypropylene (iPP) molecular chains induced by the shear field and the pre-shear temperature simultaneously affected the thermal stability of primary sheath structure. In article e10008, Yijing Qin and colleagues examined theeffects of remelting and recrystallization processes in iPP composites on the formation of β-form crystals. During tens of remelting and recrystallization processes, some crystal nuclei ofβ-form crystals could “revitalize” continuously or fitfully. Moreover, some new nucleation sitesof β-form crystals appeared from the second recrystallization process. The findings preliminarily indicated that the “crystalline memory effect” of β-form crystal might depend not only on the orientation level of molecular chains of sheath structure, but also on the spatial arrangement of fibrillar lamellae in sheath structure. (DOI: 10.1002/PCR2.10008)

Irregular ring-banded spherulites formed in poly(butylene adipate) (PBA)/poly(vinyl phenol) blends with strong hydrogen bonding. In contrast, ringless spherulites are observed in PBA/phenoxy blends with weaker hydrogen bonding strength. The formation of ring-banded structure cannot directly correlate to the hydrogen bond strength. Meanwhile, the crystallization temperature range for polymorphism is not consistent with the formation ring-band structure. Consequently, the ring-banded spherulites of PBA cannot be correlated to the coexistence of α and β crystals.

Computer simulation of polymorphism in polymers is a challenging topic. The all-atom model must be used to obtain correct crystalline structures and respective properties. The conventional molecular dynamics simulations are very slow using the all-atom model, excepting some simple polymers without side chain groups such as polyethylene and polyvinylidene difluoride. The future advances in polymorphism simulations might be based on accelerating algorithms such as metadynamics and hybrid dynamics.

In order to research the effect of ball milling and solution dispersed graphene on the PEEK crystallization process, the nonisothermal crystallization behavior for nanocomposites with different contents of graphene was investigated in this paper. As shown, the nucleation activity was increased with the addition of graphene to the PEEK matrix gradually. However, when the content of GE was 1.0 wt% in PEEK/GE② nanocomposites, the nucleation activity is the highest.

The polymorphic behavior of a β-nucleated propylene-ethylene random copolymer under shear is studied using in situ X-ray diffraction. Shear flow influences significantly on the crystal modifications: β crystals are greatly suppressed and the crystallization rate and population of α/γ crystals are enhanced by shear. Although both the β-nucleating agent and shear flow reduce the nucleation barrier of the β crystals, the combination of the two factors is detrimental for the β crystal formation.

Crystallization in polymers is a physical property that has a strong influence on other engineering properties, such as strength and degradation rate. This research shows that crystallization in copolymer films with two types of crystals is manipulated by film fabrication conditions, namely casting solvent and drying temperature. Control over the crystallization process allows for control over macroscopic properties.

Crystals of polybutene-1 Form II are able to nucleate on pre-existing seeds of Form I. We measured the nucleation induction time on Form I trigonal seeds possessing various morphologies. Form I fibers display the highest nucleating efficiency, followed by hedrites and eventually spherulites. Differences in the free energy barrier for cross-nucleation, as a result of size mismatch between the parent and daughter polymorphs' crystallites, are proposed to be the origin of the observed trend.

Polymorphism in polymers affects the material's properties and ultimate applications. Specific polymorphs can be selected using various strategies. The controlled modification of the molecular structure of polyolefins using methods of controlled synthesis that allow controlled incorporation of constitutional and/or configurational defects, may drive crystallization of a desired polymorph resulting in a tool to tailor the physical and mechanical properties of polymers.

The microphase separation and dilution effect by soft segments content and the confinements effect by low film thickness lead to the very different morphology of PA1012 crystalline phases.

Fast scanning calorimetry-optical microscope was used to determine the crystallization rate and microscale morphological change during crystallization from the highly supercooled liquid state. The crystallization rate of the blend system becomes faster than the polypropylene homopolymer at a temperature range from 50°C to 90°C. In addition, the analysis of synchrotron small and wide-angle X-ray scattering and transmission electron microscope shows the nanoscale structure and morphology of blends, comparing with that of homopolymer. These behaviors are explained using the Gibbs free energy diagram.

This study reports the polymorphic crystalline structure, phase transition, and diversified crystalline morphologies of polymorphic poly(butylene adipate) (PBA) blended with the small molecule liquid crystal, that is, 4-cyano-4′-n-pentylbiphenyl (5CB). Blending with 5CB facilitates the formation of α crystals and the heating-induced β-to-α transition of PBA in the PBA/5CB blend. Distribution of 5CB changes from the interlamellar to interspherulitic or interfibrillar regions of PBA crystals as the 5CB content increases.

Form II to form I phase transition of polybutene-1 was influenced by lamellar thickness and intercrystalline links simultaneously. The thicker the lamellar thickness, the easier the phase transition. The intercrystalline links have two opposite effects: accelerating form I nucleation in the early stage and retarding phase transition in the later stage. The role of intercrystalline links is to overcome resistance from fast dynamics of ethyl groups.

Borassus fiber powder showed significant effect as a nucleating agent for poly(lactic acid) (PLA) crystallization. It can be used as biobased nucleating agent for PLA biocomposites. Borassus/PLA composite showed faster rate of crystallization compare to neat PLA. Rate of crystallization was significantly higher at 85°C than at other isothermal temperatures.

The authors have demonstrated that it is possible to control the melt crystallization of polymers via self-nucleation. Non-covalently bonded ICs can be formed with cyclodextrins (CDs) or U hosts that crystallize around guest polymers and form narrow parallel host channels, where the isolated and stretched guest polymer chains are included. Careful removal of the hosts produce c-polymer samples that crystallize much faster than their asr-samples that they are able to nucleate.

Stereocomplex crystallization, homocrystallization, and polymorphism of enantiomeric copolyesteramides poly(l-lactic acid-co-l-alanine) [P(LLA-LAL)] and poly(d-lactic acid-co-d-alanine) [P(DLA-DAL)] copolymers with wide alanine unit content ranges from 0 to 21 and 22 mol% were investigated for melt-crystallization by wide-angle X-ray diffractometry and polarized optical microscopy. The effects of incorporated alanine units and crystallization temperature on the crystalline species, crystallinity, crystallization rate, crystalline growth geometries, and kinetics are discussed in detail.

In this work, the influence of moisture content on the thermal behavior of chitosan was investigated. It was found that the integrity of the seal of the differential scanning calorimetry pans, as well as the hydration level, plays an important role in the melting behavior of biopolymers. These results suggest that the role of water is complex depending on its state in the polymer matrix.