Preparation of urea-formaldehyde/poly(butylene succinate) and its ternary biodegradable polymer nano slow/controlled release materials by reactive extrusion

A method for preparing a biodegradable polymer binary composite urea-formaldehyde/poly(butylene succinate) or a biodegradable polymer slow release ternary nanocomposite urea-formaldehyde/poly(butylene succinate)/potassium dihydrogen phosphate by reactive extrusion, the method comprising:

• mixing two components poly(butylene succinate) and methylol-urea or three components poly(butylene succinate), methylol-urea and potassium dihydrogen phosphate uniformly, and then extruding the uniformly mixed binary or ternary mixture by a screw extruder;
• wherein the methylol-urea is melt polycondensed in the screw extruder to form urea-formaldehyde molecular chains with different polymerization degrees, and the generated urea-formaldehyde molecular chains are dispersed in a non-crystalline area of the poly(butylene succinate), and the resulting urea-formaldehyde molecular chains are mixed with the poly(butylene succinate) molecular chains in a molecular segment scale, rather than just in a simple physical blend manner;
• furthermore, for the ternary composite containing potassium dihydrogen phosphate, under shearing and mixing actions of screw of the screw extruder, the potassium dihydrogen phosphate gradually disperses and dissolves in the water generated by the melt polycondensation of methylol-urea to produce urea-formaldehyde in its surrounding environment, and then as the water evaporates at the subsequent higher temperature in the screw extruder, the dissolved potassium dihydrogen phosphate gradually precipitates out, and the growths of potassium dihydrogen phosphate crystals are restricted by the hindering of their surrounding macromolecular chain segments of urea-formaldehyde and poly(butylene succinate) and the hydrogen bond interaction between potassium dihydrogen phosphate and urea-formaldehyde, thereby resulting potassium dihydrogen phosphate crystals being confined to a nanoscale;
• and the biodegradable polymer slow release composite urea-formaldehyde/poly(butylene succinate) containing nutrient N or the biodegradable polymer slow release nanocomposite urea-formaldehyde/poly(butylenesuccinate)/potassium dihydrogen phosphate containing nutrients N, P and K is obtained;
• and
• the methylol-urea is prepared by steps of adding urea and formaldehyde aqueous solution to a reactor, adjusting the resulting solution to pH=9, reacting them at 50° C., freezing and vacuum filtering the reaction solution to obtain a filter cake, drying the filter cake, and then crushing it to obtain the methylol-urea.