| Polyvinyl chloride(PVC)is of the second largest resin after polyethylene during general-purpose plastic resins.Because of PVC's good chemical resistance,excellent flame retard,good mechanical properties and low price,it has been widely used in the fields of building materials,plates,pipes and membrane materials.However,the inherent structural defects of PVC often resulted PVC products with rigidity and poor impact resistance;the chlorine atoms with high active on side chain always caused poor thermal processing stability and resulted hydrogen chloride;PVC is also the lowest resin of heat-resistant deformation temperature among all the plastic resins.Therefore,PVC has become one with being studied and modified much more than any other plastic resins.Among above modifications,it is the most important how to improve the impact resistance of PVC.Thus,it has been a permanent subject how to enhance its impact resistanee rather than decline its heat deformation temperature and its yield strength during above modifications.So far,physical blending with ACR has still been the main and much effective method to improve the impact resistance of rigid PVC products,however,the impact resistance was still improved poorly,yield strength and the heat deformation temperature were is reduced markedly by means of physical blending method.In recently,the PVC resin with excellent impact resistance was proposed by adding latice,gained through emulsion polymerization of acrylate,to suspension polymerization system of vinyl chloride directly.Although the impact strength can exceed 40 kJ/m2,the yield strength and heat deformation temperature were still reduced at the same time.In addition,the temperature drop and sticking tank were much more serious during suspension polymerization process.Firstly,in this thesis,a series of latice based on copolyacrylate without core-shell structure and with elastic and cross-linked structure(ACR1)were prepared though traditional emulsion polymerization with the alkyl phenol polyoxyethylene ether sulfate(CO436),which is more stable than SDS to withstand dispersant during suspension polymerization,being used as emulsifier,butyl acrylate(BA)and ethyl acrylate(EA)used as the main monomers.1,4-butanediol dimethacrylate(BGDMA)used as crosslinking monomer.Then,the ACR1 is added to the suspension polymerization system and the ACR1-PVC with high impact resistance was obtained by grafting polymerization of vinyl chloride in situ,the impact strength can reach above 80kJ/m2 and the particle shape of the suspension polymerization process is satisfactory,and there was no sticking tank phenomenon,but with the predecessors As with the work,both the yield strength and the softening point were also reduced.Secondly,to enhance PVC's impact resistance,yield strength and heat-deformation temperature,the thermally reversible ion cross-linking was introduced into the PVC system.Thus,the dimethylaminoethyl methacrylate(DMAEMA)or diethylaminoethyl methacrylate(DEAEMA)contained a tertiary amino group was added on the basis of the ACR1 latex.After ACR1 introduced much more tertiary amino group,a homogeneous and cross-linked type latex(ACR2)containing tertiary amino was prepared and the suspension polymerization behavior in the presenee of ACR2 to toughen PVC in situ was studied and ACR2-PVC was achieved,active chlorine atom on PVC can easily react with the tertiary amine group on ACR2 to result a quaternary ammonium salt crosslinking bond having a thermally reversible behavior.Thirdly,in order to improve the utilization of tertiary amine groups and to obtain more active chlorine on PVC,a core-shell type tertiary amino acrylate latex(ACR3)was designed and prepared to study the suspension polymerization of ACR3 in situ toughened PVC.Thus,chloro-vinyl acetate(VCA),which containing active chlorine was introduced into suspension polymerization system and ACR3-PVC was obtained.The PVC resin particles obtained by modifying the tertiary amino acrylate latice have good morphology and the polymerization process has no sticking phenomenon.The main conclusions of above studies were as follows.1.The effect of emulsifier type on the stability of ACR1 in suspension polymerization system was investigated by conventional emulsion polymerization.The effects of the amount of feeding emulsifier and the amount of the bottom,the amount of pH buffer added and the mode of initiation on the properties of the latice were investigated.The effect of the percentage of EA in the dispersion system and ACR1 latice on the properties of ACR1-PVC resin was investigated.It was found that:1)ACR1 latice prepared by using CO436 as emulsifier has much long suspension time and high stability as well as no sticking phenomenon during suspension polymerization;2)when the total amount of CO436 is lwt%(accounting for the total acrylate by weight)and that of the bottom is o.6wt%;the particle size of the ACR1 was about 110nm,the latice gained is the most stable,and the flocculation rate is the lowest.3)The ACR1 latice prepared by thermal initiation method was more stable,and the obtained ACR1-PVC had much better impact resistance.At same time,the yield strength was the largest,and the particle morphology was also the best.When the dispersant is added in an amount of 2200 ppm to total amount of VCM monomer,the impact resistance was 27 times that of the SG-5 type resin.4)sticking tank degree during suspension polymerization of VCM can be reduced significantly with increasing the hydrophilicity of the ACR1.2.The effects of tertiary ammonia monomer types on the properties of ACR2 and ACR2-PVC were investigated and found that:1)enhancing the polymerization temperature,controlling the pH of the emulsion polymerization process was over 8,using potassium persulfate,which was the most minimal acidity increase after decomposition,the most stable ACR2 latex can be achieved;2)the polymerization stability of ACR2 by using the more hydrophobic DEAEMA is much more than that by using DMAEMA;there were no sticking tank and no sticking mixing shaft during suspension polymerization and the impact strength of the obtained ACR2-PvC resin can reach 20.6kJ/m2;3)The quaternary ammonium bond was formed in the PVC resin modified by ACR2 by infrared spectroscopy,slight yield and elongation at break,and thermal decomposition resistance.4)The yield reduction of the obtained modified PVC was smaller than that of ACR1.However,the heat-resistant deformation temperature was still effectively improved due to much little active chlorine on the PVC.3.The influence of core-shell ratio on the polymerization behavior during preparing ACR3 latex was also researched.The effects of VCA addition on the mechanical properties of ACR3-PVC were studied in detail.The core-shell structure of ACR3 was characterized by TEM.The emulsion polymerization stability was influenced by the core-shell ratio and when the ratio was 7:3(monomer mass fraction),the relatively stable ACR3 latex can easily achieved;the apparent density and tensile strength of the obtained ACR3-PVC resin were improved,the particle morphology was much better,and the suspension polymerization process is stable in presence of ACR3,but the improvement on impact resistance of PVC was not significant and the softening point is not reduced.The reason for this was that the crystallization ability of PVC was decreased after the introduction of VCA,and the amorphous component was increased. |
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