Study On The Synthesis And Compounding Of Polyether Modified Polysiloxane Defoaming Agent

Due to its unique molecular structure, polyether modified polysiloxane (PMP) has abundant advantages that other traditional defoamers like silicone defoaming agent or polyether defoamers are without parallel. It could exert excellent defoaming properties even under some extremely harsh conditions such as high temperature, strong acid or strong alkali, etc., thus making PMP a new type of anti-foaming agent with bright market prospect.In this paper a serial of polyhydrosiloxanes(PHS) with the number-average molecular weight(M_n) of 5000, and the amount of Si-H ranges from 0.05 % to 0.30 % were firstly prepared. Then a number of polyether(PE) with M_n around 1000, and the proportion of n(EO) and n(PO) ranges from 1:1 to 1:4 were synthesized with alkali as the catalyst in autoclave(EO stands for epoxy ethane, and PO stands for Propylene oxide). The final product PMP were synthesized by PHS and PE in situ from being terminated by ester group and pre-treated by antioxidants.The prior reacting conditions were explored by systematically discussing on several factors such as the content of Si-H within PHS, the peroxide value (P.V) of PE, feeding patterns and proportions of the reactants, the amount of catalysts, etc. upon the conversion of Si-H. The best conditions of hydrosilylation reaction gained are as follows: the content of Si-H ranges from 0.1 to 0.2 mol/100g, the P.V of PE less than 150 mmol/kg, n(C=C):n(Si-H)= 1.2:1 with the amount of catalyst equals to 40μg/g(calculated with the effective mass of platinum), keep the temperature stay around 80℃for about 2 hours. In this way a maximum conversion of Si-H ups to 92 % was reached.Meanwhile, studies on the surface tension, Cloud Point and other suface characteristics of PMP aqueous solution under a certain mass concentration were carried out. Based on the above data, a set of equations upon the changes of surface tension vs. temperature were derived for a series of PMP aqueous solution with varying proportions of EO and PO in the PMP molecule, providing important reference and theoretical basis for selecting an appropriate kind of PMP for practical use.This paper also focused on the compounding of PMP with other suitable anti-foaming additives to get a kind of PMP defoaming agent with good stability and high defoaming efficiency. Experiments both on defoaming ability and anti-foaming ability among silicone defoaming agent (LD200), polyether defoamer(GPE) and the self-made PMP defoaming agent were carried out in the same foaming agents under the temperature of 85℃and PH equals to 2.0 and 13.0 respectively. Results showed that the self-made PMP defoaming agent priors those two defoamers both on defoaming ability and anti-foaming ability. Plus PMP defoaming agent also showed evident advantages upon many other aspects, especially on thermal stability and centrifugal stability.Meanwhile two kinds of defoaming curves were formed by doing parallel experiments between traditional silicone defoamer and the compounding PMP defoaming agent. Relative theoretical analysis upon this phenomenon was carried out.