A Concept Of Reactive Compatibilizer-tracer For Studying The Interfacial Reaction And Evolution Of Morphology In Reactive Polymer Blending

Polymer blending is one of the most widely used methods to prepare polymer materials with high performance. However, most polymer pairs are thermodynamically immiscible, leading to phase separation and sharp decrease in the material properties. The most common method is reactive compatibilization, which results mainly from the in-situ formation of graft or block copolymer by interfacial reaction. The control of interfacial reaction and morphology during reactive polymer blending processes is very important for preparing polymer materials with high performance.This thesis reports the application of reactive compatibilizer-tracer concept for the reactive polymer blending processes to establish the relationship between mixing and the interfacial reaction and morphology. Coupling the reactive compatibilizer-tracer with the traditional concept of residence time distribution (RTD) allows us to measure evolution of morphology and interfacial reaction of the reactive polymer blend in the twin-screw extruder. The detailed results are as follows:The 9-(methylaminomethyl) anthracene (MAMA) containing fluorescent group is introduced into the styrene (St) and 3-isopropenyl-a, a’-dimethylbenzene isocyanate (TMI) copolymer (PS-TMI) to form reactive compatibilizer-tracer PS-TMI-MAMA with both compatibilizing and tracing properties. PS-TMI-MAMA is then used as a reactive compatibilizer-tracer for polystyrene (PS)/nylon 6 (PA6) (matrix/dispersed phase) blend to evaluate its efficiency. In the initial period of mixing, the amount of in-situ formed graft copolymer PS-g-PA6-MAMA increases and the dispersed phase domain size decreases. At a later stage, the number of PA6 grafts in the PS-g-PA6-MAMA increases, resulting in unstability of PS-g-PA6-MAMA at the interface. PS-g-PA6-MAMA could be pulled out of the interface to the PA6 phase and form copolymer micelles. Thus, the dispersed phase domain size increases sharply. When the density of PA6 graft of PS-g-PA6-MAMA decreases, the stability of PS-g-PA6-MAMA at interface increases. It is more difficult for PS-g-PA6-MAMA to leave the interface and degree of increase in dispersed phase domain size decreases.Mixing has dual effects on the reactive polymer blending processes. On the one hand, higher mixing speed could improve the interfacial reaction between PS-TMI-MAMA and PA6. On the other hand, it could also improve the reaction between NCO group of PS-g-PA6-MAMA and PA6 leading to the increase in the number of PA6 graft. Besides, the comb-shaped PS-g-PA6-MAMA is more unstable under higher mixing speed. Therefore the copolymer at the interface could be more easily pulled out of the interface to PA6 phase.The thesis combines the concept of the reactive compatibilizer-tracer and transient experiment of residence time distribution (RTD) to assess the the evolutions of the reactive compatibilizer-tracer content, the dispersed phase domain size, and the content of the in situ formed graft copolymer, respectively, as a function of the residence time in a twin-screw extruder using a small amounts of compatibilizer-tracer. Based on that the emulsification curve, RCC-CC curve (the content of the in situ formed graft copolymer as a function of compatibilizer-tracer concentration) and effective emulsification curve (the dispersed phase domain size as a function of the content of the in situ formed graft copolymer) could also be obtained.The method provides a powerful tool to evaluate the compaitbilizing efficiency of the reactive compatibilizers with different molecular structure in short mixing time. For a given molecular weight of copolymer, compatibilizing efficiency is higher with an appropriate increasing TMI content. For copolymer with similar reactive group content, when the molecular weight decreases appropriately, the interfacial reaction rate is faster and the dispersed phase domain size is smaller in short time.The effect of processing parameters on the interfacial reaction and morphology in the reactive polymer blending is investigated. When the ratio of throughout Q and screw speed N is fixed, the degree of fill with different throughout and screw speed is fixed. The throughout and screw speed have significant influence on the reactive polymer blending processes through the degree of fill and residence time. The effect of degree of fill is more dominant than that of residence time. As the degree of fill increases, the interfacial reaction increases and the dispersed phase domain size decreases.The distributive and dispersive mixing efficiency of different mixing elements are investigated via the evolution of the content of PS-g-PA6-MAMA formed at the interface as a function of the reactive compatibilizer-tracer content and the evolution of dispersed phase domain size as a function of PS-g-PA6-MAMA content. It indicates that when the angle of mixing elements increases, the distributive and dispersive mixing efficiency increases resulting in the increase of interfacial generation and decrease in the dispersed phase domain size based on the same amount of PS-g-PA6-MAMA. The width of kneading block decreases, the distributive mixing efficiency increases and the dispersive mixing efficiency keeps unchanged. Replacing kneading blocks by reverse ones could increase both the distributive and dispersive mixing efficiency.