Effect of melting combined with ice recrystallization on porous starch preparation: Pore-forming properties, granular morphology, functionality, and multi-scale structures

In this work, critical melting (CM) combined with freeze-thawing treatment (FT, freezing at -20 ℃ and -80 ℃, respectively) was used to prepare porous starch. The results showed that CM combined with the slow freezing rate (-20 ℃) can prepare porous starch with characteristics of grooves and cavities, while combined with the rapid freezing rate (-80 ℃) can prepare with holes and channels, especially after repeating FT cycles. Compared with the native counterpart, the specific surface area, pore volume, and average diameter of CMFT-prepared porous starch were significantly increased to 4.07 m2/g, 7.29 cm3/g × 10-3, and 3.57 nm, respectively. CMFT significantly increased the thermal stability of starch, in which the To, Tp, and Tc significantly increased from 63.32, 69.62, and 72.90 (native) to ∼69, 72, and 76 °C, respectively. CMFT significantly increased water and oil absorption of porous starch from 91.20 % and 72.00 % (native) up to ∼163 % and 94 %, respectively. Moreover, CMFT-prepared porous starch had a more ordered double-helical structure, which showed in the significantly increased relative crystallinity, semi-crystalline lamellae structure, and the proportion of the double helix structure of starch. The synergistic effect of melting combined with ice recrystallization can be used as an effective way to prepare structure-stabilized porous starch.

The Effect of Silica Nanofiller on the Physical and Thermal Characteristics of Rubber-Based Composites

The use of nano composites in elastomer blends gives outstanding mechanical properties compared to the use of micro and macro composites, even with very low nano filler content. In this paper, we studied the influence of varying proportions of natural rubber (NR) and acrylonitrile butadiene rubber (NBR) reinforced with nano silica on the mechanical and thermal characteristics of the rubber. Mechanical characterizations were carried out with hardness, tensile strength, elongation at break, tear strength, modulus and toughness. For thermal analyses, we used differential scanning calorimetry ( DSC) and Thermogravimetric Analysis (TGA). In most cases, the increase in the percentage of NBR with the presence of nano silica enhances hardness, modulus and toughness, however, it reduces tensile strength, tear strength and elongation at break. It was found that nano silica has a catalytic effect on the mixture, and NBR has a catalytic effect on the decomposition of NR.

FUNCTIONALIZED SILICA AS AN ECO-FRIENDLY VULCANIZATION ACCELERATOR TO ENHANCE THE INTERFACIAL INTERACTION IN NR/SILICA COMPOSITES

Xanthate is a class of non-toxic, rapid, and eco-friendly rubber vulcanization accelerator, but it is seldom used in the rubber industry because of its poor thermostability and ease of decomposition. To overcome these drawbacks, silica supported sodium isobutyl xanthate (silica-s-SIBX) was prepared by chemically bonding SIBX onto the silica surface. After loading, the initial degradation temperature (T0), maximum degradation temperature (Tp), and final decomposition temperature (Tf) of silica-s-SIBX were increased by 85.8, 118.9, and 146.9 °C, respectively. Meanwhile, silica-s-SIBX could not only improve the dispersion of fillers in the rubber but also enhance the interfacial interaction between silica and the rubber matrix. Therefore, it may offer new scientific and technological opportunities for preparation of green additives in the rubber industry.

Functionalized starch as a novel eco-friendly vulcanization accelerator enhancing mechanical properties of natural rubber

A novel eco-friendly vulcanization accelerator, starch supported sodium isobutyl xanthate (SSX) has been synthesized firstly. The modification of starch using sodium isobutyl xanthate (SIBX) has improved the thermal stability significantly, and the vulcanization process of natural rubber (NR) could be accelerated by SSX at 145 ℃ accordingly. More importantly, SSX can be dispersed into NR matrix uniformly along with the strong interfacial interaction between SSX and NR, as evidenced by the constrained rubber chains around SSX surface. In addition, mechanical properties of the obtained NR have been enhanced remarkably, showing a 22.4 % increase in tensile strength when compared with traditional vulcanization accelerator. Laying on the fact that a novel vulcanization accelerator has been fabricated successfully using SIBX functionalized starch, new strategies for the preparation of green vulcanization accelerators and the functional application of biopolymers can be provided.