Hydrophobic Modification of Chitosan via Reactive Solvent-Free Extrusion

Hydrophobic derivatives of polysaccharides possess an amphiphilic behavior and are widely used as rheological modifiers, selective sorbents, and stabilizers for compositions intended for various applications. In this work, we studied the mechanochemical reactions of chitosan alkylation when interacting with docosylglycidyl and hexadecylglycidyl ethers in the absence of solvents at shear deformation in a pilot twin-screw extruder. The chemical structure and physical properties of the obtained derivatives were characterized by elemental analysis, FT-IR spectroscopy, dynamic light scattering, scanning electron microscopy, and mechanical tests. According to calculations for products soluble in aqueous media, it was possible to introduce about 5–12 hydrophobic fragments per chitosan macromolecule with a degree of polymerization of 500–2000. The length of the carbon chain of the alkyl substituent significantly affects its reactivity under the chosen conditions of mechanochemical synthesis. It was shown that modification disturbs the packing ability of the macromolecules, resulting in an increase of plasticity and drop in the elastic modulus of the film made from the hydrophobically modified chitosan samples.

Stereochemistry and miscibility of epoxy resin–poly(trimethylene terephthalate) blends

Stereochemistry is proposed to contribute to the miscibility of poly(trimethylene terephthalate) (PTT) and bisphenol-A diglycidyl ether (BADGE), since molecular conformation is one of the determinants of the close packing ability and hence the interactions of such a system.

An Estimation on the Performance of High Fluidity Anti-Washout Underwater Concrete

The placing of anti-washout underwater concrete for the increasing construction of offshore foundations of long-span bridges at relatively deep sea is accompanied with significant loss of the quality of concrete as well as of the durability and reliability of the structure due to limitations brought by the workability of the high-pressure pump and the performance of the anti-washout agent. Therefore, the improvement of the performance of the underwater anti-washout agent and the development of high fluidity anti-washout underwater concrete exhibiting improved packing ability and fluidity should be implemented. Accordingly, this study focuses on the concrete for foundations applied in the RCD (Reverse Circulation Drill) method. The adequate mix proportions of a high fluidity anti-washout underwater concrete satisfying a design compressive strength of 35 MPa, slump flow larger than 600 mm and with less than 50 mg/ℓ of suspended solids is derived and the corresponding characteristics are evaluated.

Preparation of Complicated SiC Green Bodies via Aqueous Slip Casting

Two domestic silicon carbide powders with different particle size distribution and one petroleum coke powder were blended in proportion and then dispersed in aqueous medium. Green bodies were solidified from these suspensions via conventional slip casting. The effects of pH, solid loading, and the amount of dispersant on the formability and packing ability were evaluated. The results showed that the pH within 9.5-10.5, solid loading of 42vol%, aging time more than 24h, and 0.3wt% of dispersant were optimal. Complicated green bodies with height of 300mm and thickness of 3.5mm were obtained. The corresponding suspension viscosity was 1200mPa∙s and the relative packing density was 64.8%. The density is 3.01g∙cm-3 and the flexural strength is 305±15 MPa after reaction sintering. These results may be attributed to accurately using of dispersant and in-depth study of processing parameter.