Re-dispersion Mechanism And Preparations Of Re-dispersible Acrylate Latex Powders

Re-dispersible polymer latex powder is a kind of powders, which can be dispersed in water to form a stable and uniform latex, and meanwhile keeps the same properties as the original latex. It is usually synthesized by emulsion polymerization, and then prepared by spray drying after a pretreatment. The re-dispersible polymer powder is used as a kind of additive for building materials. It can be used with cement to improve the flexibility and waterproof of concrete or cement mortar, and it can also be used as powder coating, powder adhesive, etc.On the basis of the investigation of spray drying, the re-dispersibility of polymer latex powder was analyzed. An gradient emulsion polymerization was used to get gradient polymer. The gradient structure helps to improve the properities of latex and get better polymer latex powder.A pretreatment before spray drying can help to improve the drying efficiency. It includes the pH value of latex, protective colloid, and the viscosity of latex. The experimental results indicated that the best pretreatment is as follows: some NaOH solution was added in to make pH=9, 25%(wt) Silical sol and 1%(wt) Polyvinyl Alcohol(PVA) were added in, then some water was added in to make the viscosity below 350cp.The drying temperature and spray speed of spray drying were discussed. The relationship between drying temperature, spray speed and particle size, water content, filter residue content, powders re-dispersibility and film forming ability of the re-dispersion were established by a series of drying operation and characterization. The suitable drying temperature is between 120℃and 140℃and the suitable spray spray speed is between 21000rpm and 24000rpm.The study of latex powders focus on the particle size, the dosage of Methacrylic Acid, (MAA) and the pH value of redisperse latex. The experimental result indicated that adding 4-5%(wt) MAA, controling the particle size of redispersion latex below 200nm, and ensureing the pH value of pretreatment latex and redisperse latex above 9 can obviously improve the dispersibility of the powders.A gradient emulsion polymerization was used to get gradient polymer. The gradient structure was characterized via analysing the particle size in the polymerization process and the thermodynamic properties by Differential Scanning Calorimete(rDSC). The experimental results show that the performance of gradient polymer is better than homogeneous polymer and core-shell polymer. It can reduce the micro-phase separation and improves the applying performance of polymer latex powder fundamentally.