We investigated the polymer−water interaction in a model fibrous protein. Bombyx mori silk fibroin film, a typical model of biodegradable material, was cast from aqueous solution and analyzed in this study. Differential scanning calorimetry (DSC), its temperature-modulated variant (TMDSC), and the time-resolved technique of Fourier transform infrared spectroscopy (FTIR) were used for the first time to monitor the detailed structural changes of silk fibroin during heating and during isothermal crystallization above the glass transition temperature, Tg ∼ 451 K (178 °C). Results show that intermolecular bound water molecules, acting as a plasticizer, will strongly affect the secondary structure of silk fibroin. DSC study shows that silk fibroin initially displays a water-induced glass transition around 80 °C during heating, resulting from a temporary bound water-silk structure. Quantitative thermal analysis of the heat capacity changes of this system during heating revealed that no β-sheet crystals were form...

Dynamic Protein−Water Relationships during β-Sheet Formation

We have used atomic force microscopy to investigate the patterns obtained by isothermal crystallization of quasi-2-D monolayers of poly(ethylene oxide) adsorbed onto bare silicon wafers. These monolayers were prepared by a pseudo-dewetting process. Fingerlike branched structures were observed with a characteristic width which increased rapidly with crystallization temperature. The patterns are explained by a simple model considering the interplay of transport on the surface and the probability of attachment to the crystal. The influence of molecular weight was also studied. The average stem length increases with increasing temperature for the longer polymer. The shorter one crystallized in the (almost) fully extended form for all temperatures investigated. Temperature jumps during crystallization resulted in patterns with two different length scales.

Polymer crystallization in quasi-two dimensions. I. Experimental results

Temperature dependent variations in the lamellar structure of poly(l-lactide)

Structure and physical properties of syndiotactic polypropylene: A highly crystalline thermoplastic elastomer

Commercially available additives and a copolymer system were investigated for their impact on composite morphology and crystallization kinetics. This research focuses on the influence of the coupling agent and lubricants on the crystallization of polypropylene in the bulk and interphase regions and the subsequent spatial distribution of the additives. Differential scanning calorimetry and polarized light microscopy were used to determine kinetic parameters for the crystallization process of the polypropylene in the bulk composite melt and at the wood–polypropylene interface. No differences were found in the kinetics of the crystal formation nucleated on the wood surface and in the bulk polymer by polarized microscopy. Using microbeam Fourier transform infrared spectroscopy, the spatial distribution of lubricants and coupling agents were delineated. Lubricants that tended to interfere with wood–polypropylene coupling dispersed throughout the transcrystalline region around the fiber. In contrast, lubricants with lower degree of interference appeared to be phase separated in the amorphous regions between the crystals. These findings are consistent with calorimetric results that show differences in the quality of the crystals formed by the neat polypropylene.

Interaction between coupling agent and lubricants in wood–polypropylene composites

As shown by time- and temperature dependent SAXS experiments, crystals of s-PP do not change their thickness during isothermal crystallization and a subsequent heating to melting. This allows an accurate determination of the relations between crystallization temperature, crystallite thickness, rate of crystallization, and melting points. There are five main results obtained in a comprehensive SAXS and DSC investigation:  (i) Crystals have greatly varying stabilities, in spite of their uniform thickness; the first crystals melt close to the crystallization temperature. (ii) Melting points are affected by the distance to neighboring crystals. (iii) Crystals perfect during heating and annealing. (iv) Recrystallization after melting, as observed for low enough heating rates, starts with crystal growth rates that are at least 2 orders of magnitude higher than for a primary crystallization, and then slows down progressively, being accompanied by an increase in crystal thickness. (v) The dynamic signals observed...

A Four-State Scheme for Treating Polymer Crystallization and Melting Suggested by Calorimetric and Small Angle X-ray Scattering Experiments on Syndiotactic Polypropylene†

G. Strobl

Papers

A Four-State Scheme for Treating Polymer Crystallization and Melting Suggested by Calorimetric and Small Angle X-ray Scattering Experiments on Syndiotactic Polypropylene†