Protein/Protein Nanocomposite Based on Whey Protein Nanofibrils in a Whey Protein Matrix

This article describes nanocomposite films with separately grown protein nanofibrils (PNFs) in a nonfibrillar protein matrix from the same protein starting material (whey). Tensile tests on the glycerol-plasticized films indicate an increased elastic modulus and a decreased extensibility with increasing content of PNFs, although the films are still ductile at the maximum PNF content (15 wt %). Infrared spectroscopy confirms that the strongly hydrogen-bonded β-sheets in the PNFs are retained in the composites. The films appear with a PNF-induced undulated upper surface. It is shown that micrometer-scale spatial variations in the glycerol distribution are not the cause of these undulations. Instead, the undulations seem to be a feature of the PNF material itself. It was also shown that, apart from plasticizing the protein film, the presence of glycerol seemed to favor to some extent exfoliation of stacked β-sheets in the proteins, as revealed by X-ray diffraction

Enhancing Thermomechanical Properties and Heat Distortion Resistance of Poly(l‑lactide) with High Crystallinity under High Cooling Rate

In this work, a novel, effective and simple approach to largely improve the thermomechanical properties and heat distortion resistance of biodegradable poly­(l-lactide) (PLLA) by using a new nucleating agent (NA), i.e., itself high-melting-point homocrystallites (<i>h</i>PLLA crystallites) is reported. Specially, <i>h</i>PLLA crystallites with a melting temperature (<i>T</i>_m) of 187 °C were introduced into the PLLA matrix with a lower <i>T</i>_m, i.e., 168 °C via simply melt blending at 170 °C which is between the <i>T</i>_ms of the two PLLAs. Nonisothermal and isothermal crystallization results reveal that <i>h</i>PLLA crystallite is an efficient nucleating agent for PLLA. Also, <i>h</i>PLLA crystallites show much more prominently promoting effect on the crystallization rate of PLLA in comparison with two widely reported NAs for PLLA, talc and stereocomplex crystallites. Most importantly, this promoting effect is still efficient at very high cooling rate, leading to a crystallinity of 39.1% at a cooling rate of 100 °C/min, which can help to obtain high-crystallinity PLLA products in conventional manufacturing processes. The optical microscopic observation reveals that the remarkable crystallization promotion can be attributed to the outstanding heterogeneous nucleation effect, as a result of both identical chemical constitution and lattice constitution between <i>h</i>PLLA crystallites and PLLA matrix. Further characterizations indicate that the enhancement of PLLA crystallinity by using such a new efficient NA can enhance the thermomechanical properties and heat distortion resistance of PLLA remarkably. For instance, at 80 °C (above <i>T</i>_g of PLLA), the elastic modulus increases by 60 times from 8 to 477 MPa with the incorporation of 5 wt % <i>h</i>PLLA