Surface Functionalization Of Polypropylene-bearing Isocyanate Groups In Solid State And Their Application Study

Polypropylene(PP) is one of the most widely used commercial polymer because of its excellent mechanical toughness and resistance to chemical attack and aging. However, the low surface energy and non-polar chains of PP lead it to poor interface adhesion to other polar materials, which limits its use. Because of these drawbacks, more studies focused on functionalizing PP, and surface grafting can be as one of the effective methods. Melt reaction is carried out at elevated temperatures, resulting in severe PP degradation, as well as poor thermal and mechanical behaviors. Likewise, solution reaction gives off many by-products to environment, and solvent recycling needs to be done. Solid-phase reaction process is another alternative. It is usually conducted under reduced temperatures, even as low as room temperature.Such conditions reduce possibility of β-scission and lessen the degradation of PP.In this article, active groups were introduced onto PP surface by solid-state grafting method,then went on functionalization to achieve excellent PP materials, and the new surfaces were characterized systemically by applying the complementary analysis and imaging techniques. The main researches and results were shown as followed:(1) Solid-state grafting polymerization of 3-isopropenyl-α,α’-dimethylbenzene isocyanate(TMI) and styrene(St) onto polypropylene surface to prepare PP-g-TMI and PP-g-(TMI-t-St)was carried out in triethylborane/oxygen redox system; and we took the mass increase after the reaction between-NCO of TMI and-NH2 to indirectly verify the grafting ratio in quantity. The resultant materials were characterized to analyze the structure, surface morphology, thermal properties and so on, which indicated that the isocyanate groups were grafted onto PP surface successfully, and the grafting ratios climbed up as the reaction time and contents of introduced St increased. However, the grafted TMI short chains formed a disordered branched structure, which destroyed the uniform molecular structure of PP chains and caused the decline of the thermal resistance. Finally, as PP-g-TMI filled into PA6/PP blends, the dispersed particles turned smaller with less distribution. This fully demonstrated that the compatibility of blends was improved byintroducing reactive compatibilizers.(2) To achieve the special PP materials with isocyanurate layer and explore the properties of the isocyanurate coating directly prepared, we took the cyclotrimerization reaction of MDI and PP-g-TMI on the bead/membrane surfaces to synthesize a protective networked polymer with the reaction temperature, reaction time, the content of biisocyanates and post-treatment as variables.Some characterization techniques were also utilized to test the structural properties of the materials, exhibiting the existence of isocyanurates. As well, the thermal stability of the products increased slightly with the increased reaction temperature, time and MDI contents as well as with the watering treatment.(3) Taking PP-g-TMI as precursor, we used dopamine reaction with-NCO and then self-polymerization to hydrophilic modify the PP nonwovens(PP-g-TMI-PDA), and compared this method with the directly deposition in dopamine solution(PP-PDA). Based on the surface structure through ATR-IR and XPS to show the generation of PDA, we also took SEM and rheology test in an oscillatory flow to evaluate the construction of PP-g-TMI-PDA and PP-PDA.Both of the tests indicated that the former possessed more and thicker PDA layer, while the storage modulus, loss modulus, and complex viscosity of the simple PP-PDA were higher than those of PP-g-TMI-PDA, which is because small particles on the PP-PDA surface were aggregated; as a result, a heterogeneous surface was formed. Moreover, with very less loss in vapor transmission of PP nonwovens, the water hydrophilic and absoption were obviously improved with PDA layer on PP nonwoven surface.