Synthesis and properties of composites of starch and chemically modified natural rubber

The Potential Application of Starch and Walnut Shells as Biofillers for Natural Rubber (NR) Composites

The goal of this study was application of corn starch and ground walnut shells in various amounts by weight as biofillers of natural rubber (NR) biocomposites. Additionally, ionic liquid 1-butyl-3-methylimidazolium chloride (BmiCl) and (3-aminopropyl)-triethoxysilane (APTES) were used to increase the activity of biofillers and to improve the curing characteristics of NR composites. The effect of biofillers used and their modification with aminosilane or ionic liquid on the curing characteristics of NR composites and their functional properties, including crosslink density, mechanical properties in static and dynamic conditions, hardness, thermal stability and resistance to thermo-oxidative aging were investigated. Starch and ground walnut shells were classified as inactive fillers, which can be used alternatively to commercial inactive fillers, e.g., chalk. BmiCl and APTES were successfully used to support the vulcanization and to improve the dispersion of biofillers in NR elastomer matrix. Vulcanizates with starch, especially those containing APTES and BmiCl, exhibited improved tensile properties due to the higher crosslink density and homogenous dispersion of starch, which resulted from BmiCl addition. NR filled with ground walnut shells demonstrated improved resistance to thermo-oxidative aging. It resulted from lignin present in walnut shells, the components of which belong to polyphenols, that have an antioxidant activity.

Ultrafine grinding of wheat flour: Effect of flour/starch granule profiles and particle size distribution on falling number and pasting properties

In the present paper, the properties of different ultrafine flour samples, including particle size distribution, damaged starch content, falling number, and pasting properties, were examined. The results indicated that the particle size decreased significantly after jet milling, as the rotation speed and grinding time increased, and the damaged starch content significantly increased as the size of the flour/starch decreased; this is in contrast to the significant decrease in falling number. Significant differences in pasting temperature were observed between straight-grade flour (68.6°C) and five ultrafine flour samples (from 86.3 to 87.9°C). We also observed significant increases in peak viscosity, trough, breakdown viscosity, final viscosity, and setback as the flour particle size decreased from 43.07 µm to 25.81 µm (D50). The same parameters significantly decreased as the flour particle size decreased from 25.81 µm to 10.15 µm (D50). Correlation analysis identified a significant negative correlation between flour particle size (D50) and damaged starch content and pasting temperature, while a significant positive correlation was found with the falling number values. The results of this work may have an important impact on the quality of processed foods.

A new biodegradable sisal fiber-starch packing composite with nest structure

A new completely biodegradable sisal fiber-starch packing composite was proposed. The effects of fiber content and alkaline treatment on the cushioning property of the composites were studied from energy absorption efficiency, cellular microstructure and compatibility between fiber and starch. With increasing fiber content, the nest structure of composites becomes dense first and then loosens, resulting in initial enhancement and subsequent weakening of the cushioning property of the composites. The composite with 4:13 mass ratio of fiber and thermoplastic starch (TPS) exhibit the optimal cushioning property. Alkaline treatment increases the compatibility between sisal fiber and TPS, promotes the formation of dense nest structure, thereby enhances the cushioning property of the composites. After biodegradability tests for 28 days, the weight loss of the composites was 62.36%. It's found that the composites are a promising replacement for expandable polystyrene (EPS) as packing material, especially under large compression load (0.7-6 MPa).

MODIFICATION AND APPLICATION OF STARCH IN NATURAL RUBBER LATEX COMPOSITES

This study presents a review of recent studies on starch-filled NR latex composites. Starch is a renewable source of material for fillers in NR latex compounding to obtain composites with multifunctional properties for selected applications. However, starch is a non-reinforcing filler due to its large particle size. The compatibility of NR and starch is another significant issue during the processing of starch-filled NR latex composites due to the nature of both materials. However, based on our research work, a fine dispersion of starch in the rubber matrix can improve the properties of NR latex composites. A good starch dispersion can be achieved through modifications, such as physical or chemical treatments. These treatments include the ball-milling process, ultrasonic process, use of coupling agents, esterification, etherification, and graft copolymerization. The various processing methods of these composites are discussed, specifically pre-vulcanization, latex co-coagulation, and in situ polymerization process. The successful modifications of either micro- or nano-starch will improve the compatibility with hydrophobic NR matrix, thereby increasing the mechanical properties of the resulting composites. The potential of starch as a biodegradable filler for NR latex and the interparticle interaction of starch-filled NR latex composites are also discussed.

Preparation and characterization of poly(MMA-EGDMA-AMPS) microspheres by soap-free emulsion polymerization

The poly(methyl methacrylate-ethylene glycol dimethacrylate-2-acrylamido-2-methylpropanesulfonic acid) [poly(MMA-EGDMA-AMPS)] microsphere was produced by a soap-free emulsion polymerization of MMA, EGDMA and AMPS. The chemical composition, morphology, particle size distribution and properties of the obtained microspheres were characterized by energy dispersive spectrometer (EDS), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), a laser particle analyzer and thermogravimetric analysis (TGA). Results showed that the microspheres had a high-quality spherical morphology, irrespective of the components, and their particle sizes mainly ranged from 10 μm to 70 μm. The microspheres were thermally stable up to 190°C. As the AMPS loading was increased, the synthetic yield rate decreased and the water uptake increased. The optimum synthetic yield rate and water uptake were obtained at a 2.0 wt% AMPS. In addition, the selected microspheres with a diameter of approximately 25 μm provided an effective plugging, and the plugging rate was up to 80%. This study demonstrated that the plugging behavior of microspheres was due to their deformation, migration and aggregating properties in the plugging process, which made them potential materials for modifying the porous reservoir to enhance oil recovery in petroleum engineering.

Tunable nanolubrication between dual-responsive polyionic grafts

This study reports on a direct approach of quantitatively probing the nanotribological response of chemically end-grafted polyions. A combination of a quartz crystal microbalance with dissipation and atomic force microscopy, in the now well established colloidal probe mode, was utilized to investigate the stimuli-induced lubrication behavior between poly(2-(dimethylamino)ethyl methacrylate) grafts on gold. Force and friction measurements showed reversible transitions of up to an order of magnitude difference induced by varying the solvent conditions. The greatly enhanced lubrication observed at low pH was attributed to the formation of a repulsive, highly charged, hydrated cushion. At high pH the friction was significantly increased. The system turned attractive above the lower critical solution temperature with a small friction reduction interpreted as being due to nanoscopic flattening at the interfacial boundary.

Functionalization of polymer microspheres using click chemistry

We describe a new method to covalently link a wide variety of molecules to the surface of colloidal polymer microspheres using the Cu(I)-catalyzed azide-alkyne reaction, most commonly known under the class of reactions identified by the term click chemistry. The method is generic and readily applied to a spectrum of colloidal particle systems allowing surfaces to be tailored with virtually any desired functionality. To demonstrate this method, polystyrene microspheres were functionalized with two different polyethylene oxide-based polymers, and changes in hydrodynamic radii after functionalization were measured using dynamic light scattering. Control of surface functional groups was demonstrated by fluorescently labeling the colloidal microspheres using the same Cu-catalyzed azide-alkyne cycloaddition reaction.

Biocomposites of Plasticized Starch Reinforced with Cellulose Crystallites from Cottonseed Linter

Environmentally friendly starch biocomposites were successfully developed using a colloidal suspension of cottonseed linter cellulose crystallite as a filler to reinforce glycerol plasticized starch (PS). The cellulose crystallites, having lengths of 350 +/- 70 nm and diameters of 40 +/- 8 nm on average, were prepared from cottonseed linters by acid hydrolysis. The dependence of morphology and properties of the PS-based biocomposites on cellulose crystallites content in the range from 0 to 30 wt.-% was investigated by scanning electron microscopy, differential scanning thermal analysis, dynamic mechanical thermal analysis, and measurements of mechanical properties and water absorption. The results indicate that the strong interactions between fillers and between the filler and PS matrix play a key role in reinforcing the resulting composites. The PS/cellulose crystallite composites, conditioned at 50% relative humidity, undergo an increase in both tensile strength and Young's modulus from 2.5 MPa for PS film to 7.8 MPa and from 36 MPa for PS film to 301 MPa. Further, incorporating cottonseed linter cellulose crystallites into PS matrix leads to an improvement in water resistance for the resulting biocomposites. The mechanical behaviors of the starch-based biocomposites as a function of cellulose crystallites content.