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This study aimed to fabricate gum Arabic (GA)–coated Fe3O4 nanoparticles bearing numerous active aldehyde groups on their surface, followed by an assessment of their capability as a magnetic support for the covalent immobilization of the trypsin enzyme for the first time. FT-IR, XRD, TGA, and SEM results demonstrated the successful synthesis of GA-coated Fe3O4 nanoparticles, along with the covalent immobilization of the enzyme onto the support. Immobilization enhanced the relative enzymatic activity across a range of aqueous solution pH levels (ranging from 4 to 11) and temperatures (ranging from 20 to 80 °C) without altering the optimum pH and temperature for trypsin activity. Kinetic studies using Michaelis-Menten plots revealed changes in kinetic parameters, including a lower Vmax and higher Km for immobilized trypsin compared to the free enzyme. The immobilization onto magnetic gum Arabic nanoparticles resulted in an improved stability of trypsin in the presence of various solvents, maintaining a stability order comparable to that of the free enzyme due to the stabilizing effect of the support. The reusability results showed that the immobilized enzyme can retain over 93% of its activity for up to 15 cycles. [ABSTRACT FROM AUTHOR]

Here strong electroactive shape memory nanocomposites were prepared by incorporating graphene nanoplatelets into poly(vinyl acetate) ( PVAc) through the simple solvent mixing method. TEM and XRD revealed that well exfoliated graphene nanoplatelets formed a continuous network throughout the matrix with a large amount of interconnectedness. Dynamic mechanical analysis showed that the inclusion of graphene significantly improves both glassy and rubbery moduli of the matrix. Furthermore, the prepared nanocomposites demonstrated a marked electrical conductivity up to 24.7 S m−1 and thereby surprisingly rapid electrical actuation behaviour exhibiting a 100% recovery ratio in 2.5 s. Moreover, PVAc and its nanocomposites displayed scratch self-healing capability. This work demonstrates that the PVAc/graphene nanocomposites with high modulus and excellent electroactive shape memory performance can be a promising material in many applications such as sensors and fast deployable and actuating devices. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Two types of graphene were used tomake polylactic acid (PLA)–graphenenanocomposites with various concentrations of graphene through a solutioncasting method. Because of the differences in surface area, thickness,and aspect ratio between the two types of graphene, the graphene–grapheneand graphene–polymer interactions were different in these twonanocomposites. As a result, the two types of graphene nanoplateletsassembled into different interconnected structures in the matrix.Steady-state shear, stepwise small-amplitude oscillatory shear (SAOS)and large-amplitude oscillatory shear (LAOS), and frequency sweeptests immediately after the stepwise shear were used to determineand study the two different graphene aggregate structures. The disruption(under LAOS) and recovery (under SAOS) of the structures were monitoredand the great disparities between the two types of graphene were ascribedto their structural roots. The formation of a percolated graphenenetwork structure in the matrix significantly altered the structuralevolution under the stepwise shear. This multistep shear process wasfound to be a very sensitive tool to differentiate sample microstructureswhile traditional linear viscoelastic tests (i.e., SAOS) failed. [ABSTRACT FROM AUTHOR]

Despiteseveral attempts to synthesize water-expandable polystyrene(WEPS) beads, the product is still far from commercialization. Thisis mainly due to the inability of the PS beads to preserve the blowingagent (water) during storage, which leads to the loss of expandability.We report a new generation of WEPS beads with extended shelf lifeand good expandability. The beads were synthesized through Pickeringemulsion polymerization in which cross-linked starch nanoparticles(CSTNs) were used as a water-stabilizing agent. Synthesized beadswith different CSTN content could encapsulate 5.0–12 wt % ofthe water droplets of 3–4 μm in diameter. Thermogravimetricanalysis showed that the entrapped water is mainly bound water witha strong adsorption to the starch nanoparticles. Over 88% of the initialbound water content can be preserved 3 months after synthesis, therebyprolonging the shelf life of the CSTNWEPS beads. The expansion behaviorof CSTNWEPS beads was investigated in hot oil and at an optimizedtemperature of 135 °C. The best results (expansion ratio of ∼7for as-synthesized beads and ∼3 after 3 months) were obtainedfor the sample containing 1 wt % of CSTN and 5.6 wt % of water inthe form of uniformly distributed microdroplets. Finally, the morphologicalinvestigation of the expanded beads revealed that the CSTNs not onlystabilize the water microdroplets in the beads but also reinforcethe foam during expansion and inhibit cell wall rupture. [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA)-based nanocomposites comprising two different types of nanofillers, i.e. sepiolite (SEP) and nano calcium carbonate (NCC), were prepared by internal mixing and injection molding. Because of the different aspect ratio, surface area, and surface property of the nanofillers, their effects on the morphological, mechanical, dynamic mechanical, rheological, and thermal properties of the nanocomposites were shown to be very different. NCC demonstrated more uniform particle dispersion and matrix compatibility than did SEP because of the former's surface treatment, thus leading to higher strength and strain-at-failure of PLA/NCC composites. On the other hand, larger aspect ratio and surface area of SEP caused higher melt viscosity, stronger shear thinning, and better thermal resistance of PLA/SEP composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]