Effect of chitosan crosslinking time on the structure and antifouling performance of polyvinylidene fluoride membrane by surface gelation-immersion precipitation phase inversion.

Polyvinylidene fluoride (PVDF) porous membrane was prepared by a two-step method of surface gelation-immersion precipitation phase inversion. Chitosan/acetic acid solution and glutaraldehyde aqueous solution were sequentially sprayed onto the surface of the PVDF solution film, with chitosan crosslinking and gelation occurring simultaneously on the film surface. The solution film was then immersed in a coagulation bath to obtain a modified PVDF porous membrane. The effect of the crosslinking time of chitosan and glutaraldehyde on the structure and properties of the PVDF porous membrane was discussed. The results showed that with the prolongation of crosslinking time, the surface structure of the membrane changed from a dense skin layer to a porous structure; the porosity and the mean pore size of the modified PVDF membranes increased first and then decreased, and the contact angle gradually decreased. When the crosslinking time extended to 15 min, the water flux of modified membrane (M153) reached a maximum value. BSA dynamic cyclic filtration experiment showed that the retention rate (R) of the modified membrane was significantly improved, compared to 68.3% retention rate of the blank membrane (M000), but the crosslinking time had little effect on the retention rates of the four modified membranes. The antifouling data showed that the flux recovery rate of the blank membrane was 73.0%, while the flux recovery rate of the modified membrane can reach as high as 84.40%, and the irreversible pollution rate of the blank membrane was 27.7%, while the irreversible pollution rate of the modified membrane reduced to 15.6%. These results indicated that, after surface chitosan crosslinking, the hydrophilicity and antifouling properties of PVDF membranes were improved. PRACTITIONER POINTS: Modified PVDF membranes with crosslinking CS coating were prepared by a two-step method of surface gelation-immersion precipitation phase inversion. -OH groups and -NH2 groups of CS coating improve the hydrophilicity and the antifouling property of modified PVDF membranes. Modified PVDF membranes had larger mean pore size and higher porosity than unmodified membrane. Flux recovery rates of the modified membranes were higher than that of unmodified membrane. Pollution degree, reversible pollution rate, and irreversible pollution rate of modified membranes were lower than those of unmodified membrane.

Influence of Electromagnetic Inductive Microcapsules on Self-Healing Ability of Limestone Calcined Clay Cement (LC3) Mortar.

In order to promote the sustainability of cementitious materials, it is imperative to reduce the level of environmental pollution and energy consumption during their production, as well as extend the service life of building elements. This study utilized limestone, calcined clay and gypsum as supplementary cementitious materials to prepare LC3 mortar, replacing 50% of ordinary silicate cement. Three types of microcapsules (M1, M2 and M3) were prepared using IPDI as a healing agent and polyethylene wax, polyethylene wax/nano-CaCO3 or polyethylene wax/ferrous powder as shell materials. The microcapsules were added to the LC3 mortar and tested for their effects on the mechanical properties, pore structure and permeability of mortars. Pre-loaded and pre-cracked mortar specimens were subjected to room temperature or under an applied magnetic field to evaluate the self-healing ability of the microcapsules on mortars. The kinetics of the curing reaction between IPDI and moisture were investigated using quasi-first-order and quasi-second-order reaction kinetic models. The experimental results showed that the mortar (S3) mixed with electromagnetic inductive microcapsules (M3) exhibited the best self-healing ability. The compressive strength retention, the percentage of pores larger than 0.1 µm, recovery of chloride diffusion coefficient and maximum amplitude after self-healing of S3 were 92.2%, 42.6%, 78.9% and 28.87 mV, respectively. Surface cracks with an initial width of 0.3~0.5 mm were healed within 24 h. The curing reaction between IPDI and moisture during self-healing followed a quasi-second-order reaction kinetic model.

The Application of Self-Healing Microcapsule Technology in the Field of Cement-Based Materials: A Review and Prospect.

This review provides an overview of microcapsule self-healing technology and its application in the field of cement-based materials, as well as future prospects. The presence of cracks and damage in cement-based structures during service has a significant impact on their lifespan and safety performance. Microcapsule self-healing technology shows promise in achieving self-healing by encapsulating healing agents within microcapsules, which are released upon damage to the cement-based material. The review starts by explaining the fundamental principles of microcapsule self-healing technology and explores various methods for preparing and characterizing microcapsules. It also investigates the influence of incorporating microcapsules on the initial properties of cement-based materials. Additionally, the self-healing mechanisms and effectiveness of microcapsules are summarized. Finally, the review discusses the future development directions for microcapsule self-healing technology, outlining potential areas for further research and advancement.

A general QSPR model for the prediction of theta (lower critical solution temperature) in polymer solutions with topological indices.

The quantitative structure-property relationship (QSPR) study was performed between topological indices representing the molecular structures and theta (LCST, lower critical solution temperature) with a database of 169 data points including 12 polymers and 67 solvents. A linear 10-parameter model was developed to predict theta (LCST) with squared correlation coefficient (R(2)) of 0.8874 and standard error of estimation (SEE) of 24.57 for the training set of 112 systems. The mean relative error (MRE) for the calculation of theta (LCST) was 3.49%. The stability of the proposed model was validated using Leave-One-Out cross-validation and randomization experiments. The model is generally predictive and requires only topological indices during the predictions with the advantage of the relative ease in calculating descriptors which makes it easy to apply. A satisfactory MRE of 4.95% for a test set of 57 systems indicates that the model would be very useful to obtain reliable estimates of theta (LCST) in polymer solutions before they are actually synthesized.