| Natural gypsum gel material which swelling volume is slightly stable after hydrated harden not only has a strong machinability,good figuration and decoration,but also has a well fireproof and heat insulation.Meanwhile,it has some good properties of air permeability,anti-vibration,recycled and friendly to the environment.In summary,the natural gypsum is widely used in building material industry,chemical industry,medicine,art and other fields.However,the water proofing and resistance property of natural gypsum sclerotium is poor,it's easy to absorb water in wet conditions and then result in lower surface hardness.Loose,peeling and other phenomena will be appeared in severe cases that the application of natural gypsum products is greatly restricted.There are varieties gypsum waterproofing agent in the market.Gypsum products prepared by adding gypsum waterproofing agent to gypsum cementitious materials have a good waterproof performance,but the strength is lossing seriously.On the basis of the previous work on the laboratory,In the orthogonal test,using potassium persulfate(K2S2O8)as initiator,molecular structure of sodium methyl silicate waterproofing agent was grafted with styrene(St)and methyl methacrylate(MMA),synthesis of a new special gypsum orga nosilicon waterproofing agent(i.e.:Reinforced Gypsum Waterproofing Agent,short for RGW)by method of water solution polymerization which get a better synthesis conditions from the orthogonal test,the stability of synthesis conditions through experimental verification was determined finally.The samples were prepared by adding the RGW gypsum waterproof agent to the natural gypsum gel materials,testing performance of the samples on the water absorption and oven-dry flexural strength,the micro morphology of the sample sections were analyzed by XRD and analysis of RGW infrared spectra of gypsum waterproof agent.The molecular structure of waterproof agent is speculated to explore its mechanism of action.The main research conclusions are as follows:1,Under the laboratory condition,producing RGW was obtained.(a)adding amount of RGW was 1.25%and 2h,24h water absorption was measured respectively,the optimum conditions of polymerization shows;methyl sodium silicate;methyl methacrylate(MMA);styrene(St)= 1:0.16:0.04(mol:mol:mol);The dosage of initiator was 2.1%(accounted ratio of monomers,wt%);Reaction temperature is 80?.Reaction time in the bath is 5h.(b)Adding amount of RGW was 1.50%,and 2h water absorption was measured,the optimum conditions of polymerization shows:methyl sodium silicate;styrene;methyl methacrylate(MMA)= 1:0.08:0.02(mol:mol:mol);The dosage of initiator for the proportion of monomer was 2.1%(wt%);Reaction temperature is 90?.The reaction time is 5.5h.The optimum conditions of 24h orthogonal experiments is consistent with process parameters of 2h minimum water absorption except for methyl sodium silicate:styrene(St):methyl methacrylate(MMA)= 1:0.16:0.04(mol:mol:mol).2,When RGW adding amount was 1.25%,the optimum conditions of gypsum sample oven-dry flexural strength shows;methyl sodium silicate:MMA:St = 1:0.1:0.41(mol:mol:mol),The dosage of initiator was 0.9%(accounted ratio of monomers,wt%).the reaction temperature is 75?,the reaction time is 5.5h.The optimum conditions of gypsum sample oven-dry flexural strength of 1.50%RGW adding amount is consistent with process parameters of 1.25%RGW adding amount except for methyl sodium silicate:MMA:St(mol:mol:mol)= 1:0.125:0.375.3,According to the current industry standard,selectting experimental program that flexural strength higher than that of 4MPa and 2h absorption rate lower than 3.5%and 24h water absorption rate is lower than 10%from orthogonal experiment.Results of screening were NO.30th and NO.45th when adding amount of RGW was 1.25%,The process parameters for No.30th;sodium methyl silicate:MMA:St =1:0.1:0.41(mol:mol:mol),the amount of initiator is 1.3%on total monomer wt%,reaction temperature is 85 °C,the reaction time is 5.5h,the process parameters for No.45th;sodium methyl silicate:MMA:St =1:0.17:0.43(mol:mol:mol),the amount of initiator is 0.9%on total monomer wt%,the reaction temperature is 90 ?,the reaction time is 5.5h;Results of screening were NO.28th when adding amount of RGW was 1.50%,the process parameters for;methyl sodium silicate:MMA:St =1:0.14:0.26(mol:mol:mol),dosage of initiator is 0.7%(wt%)of the monomer,the reaction temperature is 75?,the reaction time is 8h.The optimal scheme for preparing waterproof gypsum samples and its dry flexural strength are better than those of commercially available products.4,Results of SEM and XRD showed that the chemical composition of natural gypsum crystal unchanged when adding RGW in natural gypsum gel materials,yet the growth of gypsum crystal was inhibited on vertical axis which result in most gypsum crystals formed columnar after hydration.Hydration gypsum crystals overlap closely.They have uniform crystal size and disorder direction.Hydration gypsum crystals have a good strength flexural lap tightly and different sizes.Many pores were formed between crystals.Waterproof effect of natural gypsum products were greatly improved compared with the blank sample.The hydration of gypsum crystal coarsening is higher,and the flexural strength is more favorable.5,Analysis of the molecular structure of RGW concluded that the double bond of MMA and St molecular structure were opened and grafted to the hydrophobic Si-O-Si network structure,ester was grafted onto the hydrophobic network under allaline conditions.Therefore,Si-O-Si hydrophobic network structure containing methyl(-CH3),(-CH2CH2C6H5),ethyl ester(-COO-),ethyl(-CH2CH3)groups.These groups were towards the outer on hydrophobic network structure,the electrostatic repulsion between atoms of alkyl act good waterproof effect.Hydrogen bonds between the ester and the substrate increased adhesion from hydrophobic network to gypsum substrate.There are groups such as phenyl steric effect improving the hydrophobic network strength,shear strength and other properties. |
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