Study On Synthesing Of Fluoroalkyl And Polyether Co-Modified Polysiloxane And Appraisal Of Its Foam Breaking And Inhibiting Performance

Polysiloxane is widely used as defoamers in aqueous system.Because it has certain solubility in oily system and it is easy to decompose in some harsh processes such as delayed coking,polysiloxane cannot be directly used as defoamers in oily system.The structure and performance of polysiloxane should be modified when used as defoamers in oily system.Fluoroalkyl modified polysiloxane would improve the characteristics of both hydrophobic and oleophobic,high stability resisting heat.The foam inhibiting ability of polysiloxane which is modified by polyether can be remarkably enhanced.Up to now,the research of polysiloxane co-modified by fluoroalkyl and polyether is relatively fewer.In this thesis,fluoroalkyl and polyether groups were grafted into polysiloxane by two-step method.In the first step,trifluoropropyl methylcyclotrisiloxane（abbreviated as D₃F）was grafted into a low hydrogen-containing silicone oil to get fluoroalkyl modified hydrogen-containing polysiloxane（abbreviated as FHPS）.In the second step,polyether group was introduced into FHPS to obtain fluoroalkyl and polyether co-modified polysiloxane（abbreviated as FPEPS）.The optimal synthesis conditions about FHPS and FPEPS were obtained by single factor and response surface analysis respectively.Various measuring methods,such as FTIR,¹H-NMR,GPC and TG,were used to test the synthetic products.In order to reduce the costs,the complex recipe of FPEPS emulsion defoamer was studied,and a cost-effective defoamer was obtained.The foam breaking and inhibiting performance between the synthetic defoamer and commercial defoamer were measured on a self-assembled equipment.Finally,the defoaming mechanism of defoamer in aqueous phase and oil phase was inferred by LB membrane analyzing and surface tension testing.The main conclusions are as following.（1）The optimal synthesis conditions of FHPS were as below:reaction temperature of 115℃,catalyst dosage of 19 mg?g^-1,dropping time of 65 min,and reaction time of 1.1 h.Under these conditions,the weight-average molecular weight was 193580,and the yield was 81.2%.Results of FTIR,¹H-NMR indicated that FHPS was successively synthesized.（2）The optimal synthesis conditions of FPEPS were as following:reactants ratio of 1.25:1,catalyst dosage of 25μg?g^-1,reaction temperature of 126℃,and reaction time of 5.6 h.Under these conditions,the conversion was 97.65%.Results of FTIR,¹H-NMR and GPC confirmed that FPEPS was successively synthesized.Results of TG showed that heat-resistant stability of the HPS was enhanced about 100℃by D₃F and PE modification.（3）After adding of the FPEPS defoamer,the foam breaking time changed from the natural defoaming time 155.8 s to 48.9 s;the foam inhibiting time was prolonged from 4.9 min to 26.3 min in aqueous system.And the foam breaking time of the oil phase system was shortened from 115 s to 15 s,and the foam inhibiting time was changed from 3.5 min to 33.2 min.（4）The best complex recipes of FPEPS emulsion defoamer were as following:10wt%of active ingredient（8wt%FPEPS+2wt%silicone paste）;4wt%of emulsifier（Span60:Tween60=1:1）;0.5wt%of thickener;85.5wt%of deionized water.After adding of FPEPS complex defoamer,the foam inhibiting time was 44.3 s and the foam inhibiting time was 31.2min in aqueous system.In oily system,the foam inhibiting time was 15.7s and the foam inhibiting time was 31.8 min.（5）Inferring from the mechanism experimental results,foam breaking and inhibiting performance of the same type defoamer has a positive correlation with its ability of reducing the surface tension of the foam system.The interface dilational modulus and dilational elasticity can be used as the main parameters to evaluate the foam breaking and inhibiting performance in industrial selection.In summary,FPEPS defoamer of better foam breaking and inhibiting performance was synthesized,which has promising industrial applications.