Preparation And Properties Of Organic - Inorganic Composite Wall Microcapsules Triggered By Chloride Ion

In concrete, chloridion is the main factor causing the corrosion of rebar. It’s expected there is a chloridion-sensltive microcapsule containing chloridion absorbent, corrosion inhibitor, or repairing additives embeded beforehand in concrete. If so, the microcapsule will release its contents spontaneously to retard the permeation or to block the diffusion path of chloridions once they make an incursion. Hence, durability of the concrete works built in high salinity area will be improved greatly. It’s clear this scheme will brings a great economic and social benefits.In this thesis, chloridion-triggered microcapsule was designed and prepared. As the microcapsule shelled by hydrophobic polymer with indissoluble veneer of metal inorganic salt, it’s very stable in water. However, when there exists chloridion, the microcapsule will be triggered. The shell will be broken because chloridion coordinate with the metal ion to form a soluble complex ion, leading to inorganic salt vanished. After water penetrates from left hole, collapse will aroused by swelling of core materials.Lead sulfate(Pb SO4) and cuprous chloride(Cu Cl) are one the few chemicals could be employed as trigger-source of chloridion. In this thesis, Pb SO4 embeded polymethyl methacrylate(PMMA) walled microcapsule containing hexadecane core and Cu Cl embeded polystyrene(PS) walled microcapsule containing epoxy E-51 core were prepared by solvent evaporation approache. The preparation process was studied in details. The parameters, such as core/shell ratio, stirring rate, surfactant and its dose, etc, were optimized, and the effect of them on microcapsule’s performance was investigated. The morphologies and structures of the two microcapsules, Hexadecane/ Pb SO4-PMMA and E-51/Cu Cl-PS, were characterized by OM, SEM, FTIR, DSC, TGA, XRD. It’s found, core/shell ratio, evaporation temperature, stirring rate, surfactant and its dose play an important role in the formation of microcapsule, in which stirring rate and surfactant dosage control the particle size, upload amount and distribution of inorganic salt particles in microcapsule shell. For the two microcapsules, the optimal synthesis condition is: core/shell ratio 1.5:1~1, stirring rate 400 rpm, surfactant 5wt% PVA, evaporation temperature 40℃, evaporation time 2.0~3.0h. Micro-mechanical test on nanoindenter shows, the hardness and Yang’s modulus of Pb SO4-PMMA composite shell are 0.036 and 2.504 Gpa respectively, of Cu Cl-PS composite shell are 0.029 and 2.01 Gpa respectively.In chloridion trigger testing, both of two microcapsules, Hexadecane/ Pb SO4-PMMA and E-51/Cu Cl-PS, exhibited very good response to chloridion when they soaked in simulated seawater. The response time in 3.5wt% Na Cl solution is 5h and 1h at respectively. Increasing the concentration of chloridion will shorten this time.