Designing and application of reactive extrusion with twice initiations for graft copolymerization of acrylamide on starch

A reactive extrusion system was designed and applied for graft copolymerization of acrylamide on starch with twice initiations. A twin-screw extruder (L/D 52) used for grafting reaction contains a weight feeder port and four holes for injecting monomer, initiator-1, initiator-2, and saponifying agent separately, as well as a devolatilization port. A single-screw extruder (L/D 15) connected with the twin-screw extruder was used to convey the products with very high viscosity. Ceric ammonium nitrate (CAN) was used as the first initiator and ammonium persulfate (APS) was used as the second initiator. This is because CAN has higher graft efficiency (GE) for modifying starch via grafting due to its high target selectivity for starch, while APS has higher reaction efficiency (RE) due to its higher activity. Saponification can be also completed during the extrusion process as long as a saponifying agent is added into the system. The chemical characterizations (RE and GE), morphologies and performances of the starch-based SAPs were investigated by FTIR, NMR, TGA, SEM, and water absorption capability. Both FTIR and NMR confirmed that AM was successfully grafted on the starch. Monomer conversion rate was up to 97.45%, RE increased by about 7.56% and GE increased by about 22.64% respectively after adding APS as the second initiator. The water absorption capacity of the SAP increased about 23.36% after adding APS. The designed reactive extrusion system solved the two well-recognized issues: 1) balance between RE and GE; 2) handling very high viscosity after saponification. The developed starch-based SAP is used to fabricate controlled release fertilizers.