甲醛交联碱木质素-聚乙烯醇-尿素薄膜氮元素缓释性能研究

Release Performance of Nitrogen from Alkaline Lignin-poly (vinyl alcohol)-urea-formaldehyde Crosslinked Film

采用交联法制备了碱木质素-聚乙烯醇-尿素-甲醛(AL-PVA-U-F)交联薄膜,分析碱木质素(AL)和交联剂甲醛(F)的加入量对氮元素缓释的影响,研究薄膜对氮元素的缓释机理,并采用XRD和FT-IR-ATR方法分析薄膜的结晶度和化学结构,结果显示碱木质素的加入可降低薄膜中氮元素的缓释速率,使氮元素达到释放平衡的时间增大,碱木质素和聚乙烯醇质量比5∶5时复合薄膜192 h时达到释放平衡,释放平衡时间最长,氮元素累积释放率最大为77.73%。加入适量的甲醛交联剂使碱木质素、聚乙烯醇、尿素、甲醛之间发生化学反应,线性和网状结构交互从而使薄膜中氮元素缓释减慢。与共混薄膜(ALPVA-U)相比,甲醛的交联作用使薄膜的结晶度降低。薄膜的氮元素累积释放率曲线呈'S'型趋势,Ritger-Peppas模型和2次多项式模型拟合较好,相关系数(R2)分别为0.976 3和0.950 9,Ritger-Peppas模型中n为0.816 7,说明氮元素释放规律是扩散和溶蚀综合作用的结果。

Alkaline lignin-poly（ vinyl alcohol）-urea（ AL-PVA-U） film was prepared by crosslinking with formaldehyd（ F）. The effects of alkaline lignin and formaldehyde on nitrogen release,as well as the release mechanism,were investigated. The films were characterized by XRD and FT-IR-ATR. The result showed that the addition of alkaline lignin limited the release of nitrogen in the film and resulted in an increase of the release balance time. The fastest release rate was observed as alkaline lignin and polyvinyl alcohol as blended with 5 ∶ 5 ratio,and the maximum release balance time as well as the highest accumulative release rate achieved under this condition represented 192 h and 77. 73%,respectively. Proper amount of formaldehyde facilitated the crosslinking among alkaline lignin,polyvinyl alcohol and urea. The formation of linear and reticular structures restricted the release of the nitrogen in the films. Compared with the blend film,the crystallinity of the crossed alkaline lignin-polyvinyl alcoholurea film decreased. The curve of nitrogen cumulative release rate displayed a S pattern. The correlation coefficients of RitgerPeppas model and Quadratic polynomial model were 0. 950 9 and 0. 976 3,respectively. The release index（ n） of Ritger-Peppas model was 0. 816 7,which indicated that the release mechanism of nitrogen was the comprehensive effects of diffusion and erosion.