Crystallization behavior of elastomeric block copolymers: Thermoplastic polyurethane and polyether‐block‐amide

Abstract

ABSTRACT:The isothermal crystallization kinetics of melt-blown webs produced from a series of elastomeric block copolymers was studied through differential scanning calorimetry (DSC). Three hardness grades were selected for a polyester and a polyether Elastollan V V R thermoplastic polyurethane and Pebax V V R polyether-block-amide copolymers. The Avrami crystallization kinetics parameters, k and n, were derived from two different methods: (1) traditional Avrami model and (2) derivative of the Avrami model proposed by Kurajica et al. (Croat Chem Acta 2002, 75, 693). The kinetic parameters from both models were consistent and showed good correlation. For all polymer types and hardness grades, crystallization kinetics were interpreted with the derivative model (Kurijica et al.) since it could be directly fitted to untransformed DSC isothermal crystallization data, and thus reduces the errors involved in Avrami analysis. The values of the Avrami exponent, n ranged between 2.59 and 3.41, indicating similar nucleation and growth mechanisms. These n values and morphological observations indicate that crystallization occurs in these copolymers in three dimensions from pre-existing nuclei and the crystals grow under isothermal conditions. This suggests that, in these elastomeric copolymers, crystallization of the hard segments drives microphase separation into crystalline and amorphous regions rather than formation of hard and soft domains.

Nonisothermal crystallization kinetics of carbon nanotubes containing segmented polyurethane elastomer

“…The Avrami exponent n has values ∼3 for neat and nanocomposite samples suggesting athermal nucleation process followed by three dimensional diffusion control growth. This observation is consistent with the earlier published works . The fractional values of Avrami exponent might be due to varied crystallite size and mixed growth and nucleation mechanism .…”

Silk and Silk‐Like Supramolecular Materials

“…Many commonly used styrene–butadiene–styrene and styrene–isoprene–styrene block copolymer TPEs (e.g., Kraton D SBS, Kraton D SIS) can show maximum strains of >1000% but have tensile strength in the range of 1–50 MPa . Stronger synthetic TPEs include poly(ether‐block‐ester) copolymers (Dupont Hytrel) and poly(ether‐block‐amide) copolymers (Arkema Pebax), which exhibit crystalline domains of the polyester or polyamide block, respectively . While these synthetic materials have high extensibility (maximum strain > 300% for Arkema Pebax), their corresponding tensile strength is ≈50 MPa.…”

Amide-containing segmented copolymers

“…[47] The crystallization behavior of Pebax® suggested the block copolymer microphase separation occurred through HS crystallization into amorphous and crystalline regions instead of the formation of hard and soft domains commonly observed in segmented copolymers. [48] The long ribbon-like PA crystalline regions provide copolymer strength upon mechanical deformation. Atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) analysis revealed the formation of nanofibrils oriented in the direction of an applied strain, which acted as the load-bearing nanostructures that dominated the mechanical properties ( Figure 3).…”