Starch nanocrystal-reinforced nanocomposites

Preparation of starch nanocrystal-reinforced NR nanocomposites is often by the solution mixing method. The general steps are depicted as follows the first step is preparation of starch nanocrystals. Starch nanocrystals were usually extracted from natural starch crops (such as maize,cassava, potato, wheat, eZc.) by hydrolysis in the presence of strong acids (such as sulfuric acid or hydrochloric acid).The second step is the mixing of the starch nanocrystal... 

Nanocomposites formed from a NR latex were filled with an aqueous suspension of waxy maize starch nanocrystals and morphology, structure and barrier properties characterized. The materials were measured in linear and nonlinear viscoelastic regions. Starch nanocrystals reinforced the NR to a content of 20 % w/w without significant loss of ultimate strain. The NR modulus was greatly increased when nano-starch was present. Starch-starch interactions were important for enhancing the composite properties. Moisture and starch nanocrystal surface chemistry were important influences on properties." ... 

Angellier H, Molina-Boisseau S, Lebrun L et al (2005) Processing and structiual properties of waxy maize starch nanocrystals reinforced natural rubber. Macromolecules 38 3783-3792 Angellier H, Molina-Boisseau S, Dole P et al (2006) Thermoplastic starch-waxy maize starch nanocrystals nanocomposites. Biomacromolecnles 7 531-539... 

NR composites and nanocomposites can be fabricated by three main techniques, namely latex compounding, solution mixing and melt blending. A variety of nanofillers, such as carbon black, silica, carbon nanotubes, graphene, calcium carbonate, organomodified clay, reclaimed rubber powder, recycled poly(ethylene terephthalate) powder, cellulose whiskers, starch nanocrystals, etc. have been used to reinforce NR composites and nanocomposites over the past two decades. In this chapter, we discuss the preparation and properties of NR composites and nanocomposites from the viewpoint of nanofillers. We divide nanofillers into four different types conventional fillers, natural fillers, metal or compound fillers and hybrid fillers, and the following discussion is based on this classification. 

The Mullins effect is characterized by stress softening. In order to demonstrate the presence of the Mullins effect in NR nanocomposites, three successive tensile cycles were performed for each sample. For the unfilled NR matrix, curves corresponding to the successive cycles were perfectly superposed, to a few per cent (6-8%) (Figure 14.22(a)).For nanocomposites, a significant decrease in G o can be observed between the first and the second cycle, for films reinforced with 30 wt% starch nanocrystals (Figure 14.22(b)).Similar to the Payne effect, the magnitude of the Mullins effect also increases with filler content. Furthermore, this increase was almost proportional to the filler content. 

LeCorre D, Bras J, Dufresne A (2011) Evidence of micro- and nanoscaled particles during starch nanocrystals preparation and their isolation. Biomacromolecules 12 3039-3046 Lee KY, Tang M, Williams CK, Bismarck A (2012a) Carbohydrate derived copoly(lactide) as the compatibilizer for bacterial cellulose reinforced polylactide nanocomposites. Compos Sci Technol 72 1646-1650... 

As observed previously, starch has been largely utilized in blends and nanocomposites with a variety of reinforcements. Less known is the ability to use starch nanocrystals (StNs) as reinforcement in polymer matrices. StNs with dimensions of a few nanometers are formed from acid hydrolysis of starch granules. These starch crystals are mainly formed of crystalline amylose, as acid hydrolysis removes the amorphous domains comprised mostly of amylopectin [172, 173]. Such StN-reinforced nanocomposites were prepared with poly(fS-hydroxyoctanoate) (PHO)... 

The cellulose based materials that are used as nano-reinforcements are cellulose nanocrystals (i.e. whiskers and nanospheres), nanofibrillated cellulose, regenerated cellulose nanoparticles and electrospun nanofibers. A wide range of polymer matrices have been used to form cellulose nanocomposites. Synthetic polymers such as polypropylene, poly(vinyl chloride) (PVC) [102], waterborne epoxy [103], waterborne polyurethane [104], polyurethane [105], poly-(styrene-co-butyl acrylate) [106], poly(oxyethylene) [107], polysiloxanes [108], polysulfonates [109], cellulose acetate butyrate [110,111], poly(caprolactone) [112], poly(viny 1 alcohol) [113] and poly (vinyl acetate) [114]. Different biopolymers such as starch-based... 

Ljungberg N, Cavaille J-Y, Heux L (2006) Nanocomposites of isotactic polypropylene reinforced with rod-like cellulose whiskers. Polymer 47 6285-6292 Lu Y, Weng L, Cao X (2005) Biocomposites of plasticized starch reinforced with cellulose crystallites from cottonseed linter. Macromol Biosci 5 1101-1107 Lu J, Wang T, Drzal LT (2008) Preparation and properties of microfibrillated cellulose polyvinyl alcohol composite materials. Compos Part A 39A 738-746 Magalhaes WLE, Cao X, Lucia LA (2009) Cellulose nanocrystals/cellulose core-in-shell nanocomposite assemblies. Langmuir. doi 10.1021Aa901928j Malainine ME, Mahrouz M, Dufresne A (2005) Thermoplastic nanocomposites based on cellulose microfibrils from Opuntiaficus-indica parenchyma cell. Compos Sci Technol 65 1520-1526 Marchessault RH, Sundararajan PR (1983) Cellulose. In Aspinall GO (ed) The polysaccharides. Academic, New York... 

The homogeneous dispersion of cellulose nanoparticles in a polymer matrix in order to obtain nanomaterials is due to their size, which allows penetration in hydrosoluble or at least hydrodispersible structures (as latex-form polymers) as well as dispersion of polysaccharide nanocrystals in nonaqueous media especially using surfactants and chemical grafting. Thus, one of the processing techniques of polymer nanocomposites reinforced with polysaccharide nanocrystals was carried out using hydrosoluble or hydrodispersible polymers. In this respect, the literature has reported preparation of polysaccharide particles with reinforced starch (Svagan et al. 2009), silk fibroin (Noishiki et al. 2002), poly(oxyethylene) (POE) (Samir et al. 2006), polyvinyl alcohol (PVA) (Zimmermann et al. 2005), hydroxypropyl cellulose (HPC) (Zimmermann et al. 2005), carboxymethyl cellulose (CMC) (Choi and Simonsen 2006), or soy protein isolate (SPI) (Zheng et al. 2009). 

The reason for the nanocomposites increased thermal properties is associated to the relocation of the plasticizer(s), water inclusive, from the starch matrix to the cellulose nanocrystals surfaces, which decreases the plasticization effect on the amorphous regions (Angles and Dufresne 2000, 2001). They proposed the formation of the transcrystaUine zone, around the cellulose nanofillers in order to explain the results obtained in plasticized waxy maize starch reinforced with tunicin nanowhiskers. This effect is caused by the recrystallization of amylopectin chains assisted by the plasticizer accumulation and the nucleating effect of C-NW. 

Cao X, Chen Y, Chang PR, Muir AD, Falk G (2008b) Starch-based nanocomposites reinforced with flax cellulose nanocrystals. express Polym Lett 2 502-510... 

Slavutsky et al. (2014) prepared starch/cellulose nanocrystals (CNCs) films and their water barrier properties were studied. The measured film solubility, contact angle, and water sorption isotherm indicated that reinforced starch/CNC films have a lower affinity to water molecules than starch films. Permeability, dififusivity, and solubility coefficients indicated that the permeation process was controlled by the water diffusion and was dependent on the tortuous pathway formed by CNC incorporation. The decrease in surface hydrophilicity and the improvement in water vapor barrier properties with the addition of CNC showed that these nanocomposites present excellent potential as a new biomaterial for application in food packaging and conservation. 

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