| Some polymer materials can improve the structure of sandy soil and have it stabilized to resist erosion, therefore they have bright application prospect on combating desertification. In order to reduce the cost of such materials, in this study two categories of cheap polymers namely urea-formaldehyde resin (UF) and by-products of pulping industry were used as starting materials, and through appropriate chemical modifications, to prepare new and efficient polymer materials for stabilizing sandy soil.Two new kinds of sulfonated amino-formaldehyde resins that were respectively named as SUF and SMUF were innovatively prepared through low-degree sulfonation of UF intermediate and addition of some melamine in UF reaction system, with the aim of improving the water dispersibility of UF as well as its performance on stabilizing sandy soil. The mechanisms of sulfonation and modification were investigated, and correspondence between structural units and peaks in their 13C-NMR spectrograms was analyzed. The major technical factors influencing the preparation of above sulfonated products were discussed, and proper ratios of raw materials and optimized reaction conditions were recommended. The influence of properties of products on their performance on improving structure of sandy soil was investigated. According to analytical results from both dry and wet sieving methods, the proper theoretical degree of sulfonation of SUF and SMUF products was between 14.0% ~ 18.0%. If 20% (in weight to urea) melamine was added in the preparation of SUF, its effect on improving structure of sandy soil was enhanced by above 50%. If the application rate of SMUF168 wherefrom was 0.3%, the dry and wet contents of aggregates (COAs) >0.25 mm in sandy soil were respectively 48.3% and 42.0%, which met the higher level of soil in ordinary arable layers.The graft copolymerization of lignosulfonates (LSs) with acrylic monomers was studied with the target application on stabilizing sandy soil, and using this same method the spent sulfite liquors (SLs) were directly modified for the first time. It was proposed that the most important factor influencing above modifications was the selection and dosage of initiator. After graft copolymerization with 80% (in weight to LS or dry SL) acrylic monomers, theLS's capacity on improving structure of sandy soil was enhanced by 3 times, and SL's capacity by 4 times. Their graft copolymerization with dual monomers and products' performance on improving structure of sandy soil were investigated. According to analytical results from both dry and wet sieving methods, it was recommended that the monomer ratio of AM and AA should between 60/20 ~ 80/20 (percentage in weight to LS or dry SL). When application rates of SLS-AM60AA20 and BSL-AM80AA20 were both 0.2%, the dry and wet COAs in sandy soil were respectively 47.1% and 40.0%, 49.8% and 43.1%, which met the higher level of soil in ordinary arable layers.The acting mechanism of polymers on stabilizing sandy soil was discussed at three aspects namely intermolecular action, polymer properties and interface action. It was proposed that, in dry status the bonding of anionic groups onto sand grains was stronger than that of non-ionic groups, but excessive content of anionic groups would reduce the water stability of sandy soil treated by polymers. It was innovatively proposed that the adhesive theory could be applied to explain the action of polymers on sand grains in dry status. The SMUF168 product prepared in this study had much higher performance/cost ratio (the dry P/C ratio was 130.4%, and wet P/C ratio 104.6%) on improving structure of sandy soil than some commercial polymers and other self-made products. BSL-AM80AA20 product had the dry P/C ratio (102.0%) very close to that of anionic polyacrylamide (APAM, 100.0%), which was the best among those commercial polymers. The BSL-AM80AA20 product also had outstanding potential on environmental and social benefits due to the harmless utilization of SLs. Through simulated wind erosion test, it was found tha...
|
PDF Full Text Request