Acrylamide Synthesize High Molecular Weight And Low Toxicity (Food Grade) Of Polyacrylamide By The Method Of Aqueous Solution Polymerization

Polyacrylamide (PAM) solution has high viscosity, thickening, flocculation andother important performance.It can be widely used in modern industry and agriculturefields, include sewage disposal, petroleum exploitation, papermaking, alkali making,refine sugar, coal washing, ore dressing, soil improvement, moisture absorption andso on. It’s very important for the development of national economy. Most of the time,the molecular weight is the longer the better. So improving molecular weight has beenan important task since1950s. As a result of the toxicity of acrylamide, so we alwayshope rudimental acrylamide in the polymer is the less the better no matter in what theapplication field.There has strict rules for the residual quantity of acrylamide in thefood and drinking applications. PAM is stored and transported mainly in dry powderform, but it often need to dissolve in water before use, therefore, we hope the lysistime is shorter,and the insolubles is as little as possible. It will be seen from this thathigh molecular weight, low monomer residue and instant polyacrylamide is commonrequirements in the most applications.The experimental prepared of polyacrylamide by water solution polymerization,respectively uses five kinds of redox initiator system，APS（Ammonium persulfate）—DA（1,2-did(dimethylamino)ethane），APS—PMS（potassium metabisulfite），APS—SBS（Sodiumbisulfite），PPS（Potassium persulfate）—PMS and PPS—DA。By comparison, adopting the APS—DA trigger system can get the highest molecularweight,then is APS—PMS. Reducing agent plays a major role on the polymerizationrate, the fastest polymerization rate is DA,the slower is PMS and SBS, each system isno significant effect on the conversion rate. From the performance of polymerizationproducts, APS-DA is the best initiator system, but taking into account the toxicity ofDA,the practical application is limited,so we finalize the best polymerization systemis APS—PMS.And the best polymerization condition is23%of the monomerconcentration, APS (0.08%)-PMS (0.08%) initiator system,0.2%of the ammoniaconcentration,40℃,8h and pH10. Now the molecular weight of PAM is1300~1500, conversion rate is close to100%and without insolubles. In addition,the molecularweight can achieve about19,000,000when we use the lower monomer concentrationor lower temperature polymerization.We see about the impact of impurities on the polymer in the best polymerizationcondition, Fe3+and hydrocyanic acid have little effect on molecular weight in theinvestigation, organic impurities include acrylonitrile, acrylic acid, β-hydroxypropionitrile, acetonitrile and acetone cause significant impact on molecular weightwill require achieve the higher concentration(above1000ppm). Commonly,themonomer of AM does not exist such high concentration of impurities,so we can notconsider the impact of these impurities on the molecular weight when we use watersolution polymerization.Only Cu2+has significant effect on PAM molecularweight,its concentration must be strictly controlled under0.2ppm. In all theexperiments,we do not find the conversion rate is significantly reduced caused byimpurities.We analyse the structure and performance of PAM caused by APS—DA andAPS—PMS system. By analysis of the infrared spectrum,both polymerizationproducts leading by different initiation system have basically the same structure,andthe main component is PAM. From the TGA analysis,the TG curves of the twopolymers is very close: the sample is not decomposition before200℃, it isdeamination between200℃and300℃,and losing some weight,it is fast losingweight between300℃and450℃,and it is almost completely carbonized at450℃.The changes are comparatively match with the theoretical value,indicating thepolymers has good thermal stability.From gas chromatography,we find the AM leavedis lower than0.05%in both polymerization products leading by different initiationsystem,indicating it reach the food grade in residual monomer.