Speeding of Spherulitic Growth Rate at the Late Stage of Isothermal Crystallization Due to Interfacial Diffusion for Double-Layer Semicrystalline Polymer Films

In this study a unique phenomenon has been found for isothermal crystallization of double-layer semicrystalline polymer films. It is surprisingly found that there exists a speeding of poly­(l-lactic acid) (PLA) spherulitic growth rate for poly­(ethylene oxide)/poly­(l-lactic acid) (PEO/PLA) double-layer films at the late stage of isothermal crystallization, which does not exist for PLA/PEO blend films and neat PLA films. The mutual diffusion between PEO and PLA layers plays the key factor to bring out the observed speeding of spherulitic growth rate. This type of study provides an avenue for understanding the interplay between polymer crystallization and interfacial diffusion in multilayer polymer films, which is not available when employing the polymer blend films

Bioinspired Design of Nanostructured Elastomers with Cross-Linked Soft Matrix Grafting on the Oriented Rigid Nanofibers To Mimic Mechanical Properties of Human Skin

Human skin exhibits highly nonlinear elastic properties that are essential to its physiological functions. It is soft at low strain but stiff at high strain, thereby protecting internal organs and tissues from mechanical trauma. However, to date, the development of materials to mimic the unique mechanical properties of human skin is still a great challenge. Here we report a bioinspired design of nanostructured elastomers combining two abundant plant-based biopolymers, stiff cellulose and elastic polyisoprene (natural rubber), to mimic the mechanical properties of human skin. The nanostructured elastomers show highly nonlinear mechanical properties closely mimicking that of human skin. Importantly, the mechanical properties of these nanostructured elastomers can be tuned by adjusting cellulose content, providing the opportunity to synthesize materials that mimic the mechanical properties of different types of skins. Given the simplicity, efficiency, and tunability, this design may provide a promising strategy for creating artificial skin for both general mechanical and biomedical applications

Bioinspired High Resilient Elastomers to Mimic Resilin

Natural resilin possesses outstanding mechanical properties, such as high strain, low stiffness, and high resilience, which are difficult to be reproduced in synthetic materials. We designed high resilient elastomers (HREs) with a network structure to mimic natural resilin on the basis of two natural abundant polymers, stiff cellulose and flexible polyisoprene. With plasticization via mineral oil and mechanical cyclic tensile deformation processing, HREs show ultrahigh resilience, high strain, and reasonable tensile strength that closely mimic natural resilin. Moreover, the mechanical properties of HREs can be finely tuned by adjusting the cellulose content, providing the opportunity to synthesize high resilient elastomers that mimic different elastic proteins, such as elastin

Preparation of Novel Cross-Linked and Octylated Caseinates Using a Biphasic Enzymatic Procedure and Their Functional Properties

A novel microbial transglutaminase-catalyzed aqueous–organic biphasic reaction system was successfully developed to prepare caseinate derivatives by cross-linking and incorporating nonpolar octyl tails for the first time. SDS-PAGE and ¹H NMR analysis confirmed that cross-linking and octyl conjugation occurred simultaneously. The octyl substitution degree (SD) was measured by ¹H NMR and used as an index to determine a suitable reaction condition. It was found that at the condition of 0.125% (w/v) protein concentration and 6 h of reaction time, the modified caseinate had the highest SD of 28.96%. The modified caseinate also had an increased surface hydrophobicity, better emulsifying activity, and improved thermal and salt stabilities. However, its emulsion stability or in vitro enzymatic digestibility was slightly lower than that of the native caseinate

Critical Content of Ultrahigh-Molecular-Weight Polyethylene To Induce the Highest Nucleation Rate for Isotactic Polypropylene in Blends

The influence of the addition of low amounts of ultrahigh-molecular-weight polyethylene (UHMWPE) on the crystallization kinetics of isotactic polypropylene (iPP) in iPP/UHMWPE blends has been investigated by means of differential scanning calorimetry (DSC) and polarized optical microscopy. During the nonisothermal crystallization process, the primarily formed UHMWPE crystals serve as heterogeneous nucleating agents for iPP nucleation, whereas during the isothermal crystallization process, UHMWPE is in the molten state, iPP nucleation preferentially occurs at the UHMWPE and iPP phase interfaces, and the spherulitic growth rates are not obviously affected. It is particularly interesting to find a critical UHMWPE content (2.5 wt %) in the blends to induce the highest iPP nucleation rate; however, above the critical UHMWPE content, the iPP nucleation rate slows because of aggregation of the UHMWPE component. A delicately designed DSC measurement provides insight into the nucleation mechanism of iPP at the interfaces between the UHMWPE and iPP phase domains. It is proposed that the concentration fluctuations generated from the unstable inhomogeneous phase interfaces in the iPP/UHMWPE blends promote the formation of nuclei, which eventually enhances the nucleation and overall crystallization rates of the iPP component

Structural, Thermal, and Anti-inflammatory Properties of a Novel Pectic Polysaccharide from Alfalfa (Medicago sativa L.) Stem

A pectic polysaccharide (APPS) was purified from the cold alkali extract of alfalfa stem and characterized to be a rhamnogalacturonan I (RG-I) type pectin with the molecular weight of 2.38 × 10³ kDa and a radius of 123 nm. The primary structural analysis indicated that APPS composed of a →2)-α-l-Rha<i>p</i>-(1→4)-α-d-Gal<i>p</i>A-(1→ backbone with 12% branching point at C-4 of Rha<i>p</i> forming side chains by l-arabinosyl and d-galactosyl oligosaccharide units. Transmission electron microscopy (TEM) analysis revealed a primary linear-shaped structure with a few branches in its assembly microstructures. The thermal decomposition evaluation revealed the stability of APPS with an apparent activation energy (<i>E</i>_a) of 226.5 kJ/mol and a pre-exponential factor (<i>A</i>) of 2.10 × 10²⁵/s, whereas its primary degradation occurred in the temperature range from 215.6 to 328.0 °C. In addition, APPS showed significant anti-inflammatory effect against mRNA expressions of the pro-inflammatory cytokine genes, especially for IL-1β, suggesting its potential utilization in functional foods and dietary supplement products

Significantly Accelerated Spherulitic Growth Rates for Semicrystalline Polymers through the Layer-by-Layer Film Method

The influence of a molten liquid polymer layer on the crystallization of the beneath semicrystalline polymer has been seldom considered. In the study, the nucleation and growth of spherulites for the beneath polylactide (PLA) layer in poly­(ethylene oxide)/polylactide (PEO/PLA) double-layer films during isothermal crystallization at various temperatures above the melting point of PEO have been investigated by using polarized optical microscopy, with the particular results compared with that for neat PLA and PLA/PEO blend films. It is interesting to find that the top covering molten PEO layer can greatly accelerate the spherulitic growth rate (<i>G</i>) of the beneath PLA layer. Another significant result is that the temperature for the measurable nucleation and spherulitic growth of PLA in the double-layer films can be eventually pushed down close to the glass transition temperature of neat PLA. The changes of glass transition temperature, <i>T</i>_g, for PEO/PLA multilayer films have been measured by using modulated differential scanning calorimetry and dynamic mechanical analysis, which reveal slight decreases of <i>T</i>_g for PLA layer due to the influence of PEO layer. The layer structures of fractured surface of the double-layer films are analyzed on the basis of the observation from scanning electron microscopy, and the existence of interdiffusion areas with irregular boundary between PEO and PLA layers is the key clue to understanding the significant acceleration of <i>G</i> for PLA. The layer-by-layer film method infers promising applications, which might be considered to well replace the blending method

Fabrication of Copolymer-Grafted Multiwalled Carbon Nanotube Composite Thermoplastic Elastomers Filled with Unmodified MWCNTs as Additional Nanofillers To Significantly Improve Both Electrical Conductivity and Mechanical Properties

Nanostructured materials have attracted tremendous attention in past decades owning to their wide range of potential applications in many areas. In this study, novel conductive composite thermoplastic elastomers (CTPEs) were fabricated by using a copolymer-grafted multiwalled carbon nanotube (MWCNT) composite thermoplastic elastomer filled with varied amounts of unmodified MWCNTs as additional nanofillers. Rheological measurements and electrical conductivity tests were performed to investigate the viscoelasticity and electrical percolation behavior of these CTPEs, respectively. The incorporation of unmodified MWCNTs can significantly increase the electrical conductivity of these CTPEs, and the electrical conductivity percolation threshold was determined to be 0.34 wt %. The macroscopic mechanical properties of these CTPEs can be conveniently adjusted by the content of unmodified MWCNTs; for example, the strain-hardening behavior can be significantly enhanced with the incorporation of unmodified MWCNTs. This design concept can be generalized to other conductive composite elastomeric systems

A Novel Alkaline Hemicellulosic Heteroxylan Isolated from Alfalfa (Medicago sativa L.) Stem and Its Thermal and Anti-inflammatory Properties

A novel hemicellulosic polysaccharide (ACAP) was purified from the cold alkali extraction of alfalfa stems and characterized as a heteroxylan with a weight-average molecular weight of 7.94 × 10³ kDa and a radius of 58 nm. Structural analysis indicated that ACAP consisted of a 1,4-linked β-d-Xyl<i>p</i> backbone with 4-<i>O</i>-MeGlc<i>p</i>A and T-l-Ara<i>f</i> substitutions at <i>O</i>-2 and <i>O</i>-3 positions, respectively. Transmission electron microscopy (TEM) examination revealed the entangled chain morphology of ACAP molecules. The evaluation of thermal degradation property revealed a primary decomposition temperature range of 238.8–314.0 °C with an apparent activation energy (<i>E</i>_a) and a pre-exponential factor (<i>A</i>) of 220.0 kJ/mol and 2.81 × 10²⁴/s, respectively. ACAP also showed significant inhibitory activities on IL-1β, IL-6, and COX-2 gene expressions in cultured RAW 264.7 mouse macrophage cells. These results suggested the potential utilization of ACAP in functional foods and dietary supplement products

Thermoactivated Electrical Conductivity in Perylene Diimide Nanofiber Materials

Thermoactivated electrical conductivity has been studied on nanofibers fabricated from the derivatives of perylene tetracarboxylic diimide (PTCDI) both in the dark and under visible light illumination. The activation energy obtained for the nanofibers fabricated from donor–acceptor (D–A) PTCDIs are higher than that for symmetric <i>n</i>-dodecyl substituted PTCDI. Such difference originates from the strong dependence of thermoactivated charge hopping on material disorder, which herein is dominated by the D–A charge-transfer and dipole–dipole interactions between stacked molecules. When the nanofibers were heated above the first phase transition temperature (around 85 °C), the activation energy was significantly increased because of the thermally enhanced polaronic effect. Moreover, charge carrier density can be increased in the D–A nanofibers under visible light illumination. Consistent with the theoretical models in the literature, the increased charge carrier density did cause decrease in the activation energy due to the up-shifting of Fermi level closer to the conduction band edge