Pea starch nanocrystals (StNs) were incorporated into a soy protein isolate (SPI) matrix to produce a class of full‐biodegradable nanocomposites. The StN with low loading level (2 wt%) showed a predominant reinforcing function, resulting in an enhancement in strength and Young's modulus. This was attributed to uniform dispersion of StN in the amorphous region of the SPI matrix, as well as maintaining stress of the rigid StN and transfer of stress mediated by interfacial interaction between the active StN surface and the SPI matrix. As a result, the nanocomposite containing 2 wt% StN had the maximum strength and Young's modulus in all the materials. With an increase in StN content, the number and the size of StN domains simultaneously increased due to a strong self‐aggregation tendency of StN. It lowered the effective active StN surface for interaction with the SPI matrix and destroyed the ordered structure in the SPI matrix, resulting in a gradual decrease of strength and Young's modulus. The introduction of relatively hydrophilic StN did not cause an obvious decrease of water resistance for any of the nanocomposites. The water uptake behavior of all the nanocomposites similar to that of neat SPI material was attributed mainly to the strong interfacial interaction between the StN filler and the SPI matrix. POLYM. COMPOS., 2009. Published by the 2008 Society of Plastics Engineers
Poly(ε‐caprolactone) (PCL) was grafted to the surface of starch nanocrystals (StN) via microwave‐assisted ROP. The resultant nanoparticles were then incorporated into a poly(lactic acid) matrix to produce fully‐biodegradable nanocomposites with good mechanical properties. A loading level of 5 wt.‐% StN‐g‐PCL resulted in simultaneous enhancements of strength and elongation. The StN‐g‐PCL self‐aggregated as rubbery microparticles to enhance the elongation by ca. 10‐fold over that of neat PLA. Meanwhile, the grafted PCL chains were miscible with PLA and formed a stress‐transferring interface to the StN, providing a reinforcing function.magnified image
Based on a ''graft from'' strategy, the surface of starch nanocrystals (StN) were functionalized by grafting with polycaprolactone (PCL) chains via microwave assisted ring-opening polymerization (ROP). The modified natural nanoparticles were then compounded into a PCL-based waterborne polyurethane as matrix. The structural and mechanical properties of the WPU/StN-g-PCL nanocomposites were characterized by XRD, FTIR, SEM, DSC, DMA, and tensile testing. It was interesting to note that a loading-level of 5 wt % StN-g-PCL resulted in a simultaneous enhancement of tensile strength and elongation at break, both of which were higher than those of neat WPU. This enhancement was attributed to the uniform dispersion of StN-g-PCL because of its nano-scale size, the increased entanglements mediated with grafted PCL chains, and the reinforcing function of rigid StN. Increasing the StN-g-PCL content however caused the StN-g-PCL to self-aggregate as crystalline domains, which impeded improvement in tensile strength and elongation at break, but significantly enhanced Young's modulus.
The nano-SiO 2 particles were compounded into soy protein isolated (SPI) matrix to produce a series of reinforcing nanocomposite sheets by compression-molding. Except for the expected increase of strength and modulus, the elongation was also enhanced when the nano-SiO 2 content was lower than 8 wt %. Moreover, two nanocomposite materials were recommended: the one is a nanocomposite containing 4 wt % nano-SiO 2 with the highest strength and enhanced elongation, the other is a reinforced material with the best elongation filled by 8 wt % nano-SiO 2 . The increase of nano-SiO 2 content produced many kinds of distributions in SPI matrix, such as single nanosphere, $ 100 nm nanocluster, interconnected network structure and great domain. Such structures strongly affected the mechanical performances of nanocomposite materials. The simultaneous enhancement of strength and elongation was related to homogeneous dispersion of nanoclusters while aggregated great domains severely decreased elongation in spite of obvious reinforcing effect. However, the reinforced materials with high loading of inorganic filler should be paid attention and have economic value to some extent in practical application. With the changes of nano-SiO 2 distribution, the structures of SPI matrix changed as well. After adding a mall amount of nano-SiO 2 , the damage of glycerol plasticization to ordered structure of SPI was reduced. But as nano-SiO 2 content increased, the SPI microphase was separated from nano-SiO 2 domains. Furthermore, the condition of simultaneous reinforcing and toughening was put forward: the moderate aggregation of nano-SiO 2 as well as all kinds of strong interfacial interactions.
MWNTs of various sizes were compounded into SPI matrix by solution mixing and then compression‐molded into nanocomposite sheets, which were characterized by XRD, SEM, TEM, and tensile and water uptake testing. The resultant nanocomposites showed improved mechanical performance and higher water resistance depending on MWNT size and content. This work details a strategy to achieve improved performance, especially in terms of mechanical properties, using MWNTs of various sizes to regulate the entanglement and penetration between SPI and MWNTs.magnified image
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