Near-infrared Spectroscopy Applied In Core/Shell Latex Research

Core-shell latex particles have excellent properties and are essential for the preparation of high-performance coatings.Although the scientific research and preparation of core-shell latex particle is relatively mature,however,how to monitor the process of emulsion polymerization and control phase separation is still lack of effective method.Near infrared spectroscopy and chemometrics method were combined to study the phase separation process of core-shell particles,and the effect of polymerization process on phase separation in this paper.The dissertation includes but not limit to the following contents:1.The core-shell latex particles with various weight fractions of the core phase(Wc),the shell phase(Ws),and the interfacial phase(Wi)between core matrix and shell layer were synthesized via seeded semi-continuous emulsion polymerizations.The basic data for near infrared calibration models of latex were required through using dynamic light scattering,multi frequency modulated temperature differential thermal scanner,gas chromatography,nuclear magnetic resonance spectroscopy.The results show that the structural size is influenced by emulsifier content and monomer ratio.The particle size becomes smaller with higher content of emulsifier,and the higher of BA monomer is,the higher the content of interfacial phase.Moreover,the polymerization rate can be increased with increasing initiator or the ratio of MMA,resulting in the decrease of residual monomer in the system and the increase of instantaneous solid content.2.Combined with partial least squares(PLS)and near infrared spectroscopy,he NIR calibration models of core-shell structure latex particle size,the weight fraction and thickness of each phase,residual monomer content,copolymer composition and solid content with good prediction results were established in this paper.It proved that it is feasible to use near infrared spectroscopy to study core-shell latex particles.3.These calibration models were employed to on-line analyze the structural evolution of core-shell latex particles in emulsion polymerization process.It is found that there were four stages in core-shell latex structural evolution.In the early stage of emulsion polymerization,the effect of kinetic factor,shell layer starts to increase and interfacial layer stays constant.In the second steps,interfacial starts to increase because monomer diffusion on the surface of core matrix.In the late stage,the weight fraction of shell layer stops increasing and the weight fraction of interfacial phase increases continuously.Finally,all of the phases reach equilibrium.The weigh fraction of interfacial phase would decrease with depressed monomer addition rate,as well as the improvement on the glass transition temperature of shell polymers or core polymers.4.Online detect of the residual monomer content showed that the amount of emulsifier has no influence on the residual monomer content of the system,and the content of residual monomer will reduce with decreased monomer dropping rate,as well as increased initiator and reaction temperature.