纳米限域条件下原位反应包膜控释材料的探索及机制研究

Mechanical properties of the film play a key role in improving the performance of slow-release polyurethane encapsulated fertilizer. But in the in situ polymerization film-forming process, it is not easy to control the reaction rate between raw materials, thus the surface of fertilizer is unevenly covered, which makes an effect of high coating ratio. Our initial studies have found that the mesoporous molecular sieve with nano channel structure is an excellent modifier in improving the performance of polyurethane materials. Accordingly, herein a hypothesis of nano-confined particle is put forward, that is, hydroxyl groups of organic template confined in the mesopores of molecular sieve firstly react with -NCO group of isocyanate, followed by the formation of polymer in the method of chain extension. So the chain of polyurethane can be connected with molecular sieve firmly. The methods of FT-IR, SEM, XPS and TG-DSC are used in order to research the connection of interface, dispersion of molecular sieve and microphase separation, and the release extraction of nutrient in water and tensile test are applied to investigate properties of film, thus the feasibility of nano-confinement in improving the controlled release performance of coating material is explored, which has an important significance in clarifying the internal mechanism of in-situ polymerization film-forming process in the surface of mesoporous molecular sieve and revealing the relationship between the controlled release performance of material and morphological structure. In addition, a brand-new concept is provided to research the controlled release coating materials with low cost and high performance.

选择力学性能优良的膜材是聚氨酯薄膜包衣控释肥制备中的关键，但是在原位反应成膜过程中原料间的反应速率和程度不易控制，使得肥料表面膜层覆盖很难均匀，导致膜层质量不高。我们前期研究发现具有纳米孔道结构的分子筛是聚氨酯性能提高的优良改性剂。据此提出了"纳米限域粒子"假说，即利用限域于介孔分子筛孔道内有机模板的端羟基与异氰酸酯原位反应，再扩链成大分子，使聚氨酯链段与分子筛牢固相连，从而制备纳米限域聚氨酯包膜控释材料。拟采用FTIR、SEM、XPS和TG-DSC等方法进行分子筛用量、形态结构和官能团含量等因素对包膜材料的结构的影响、采用水泡法以及拉伸试验等对包膜材料的性能的影响进行研究，探索纳米限域在提高膜材质量方面的可行性，对阐明分子筛对聚氨酯原位反应成膜的作用机制、揭示包膜材料形态结构与其性能和成膜过程间的关系有重要意义，为新型低包膜率和高质量包膜控释材料的研制提供全新思路。

针对我国化肥用量大、利用率低等问题，围绕肥料缓释增效进行的控释肥技术得到了提升，价廉质高的膜材是当前聚氨酯薄膜包衣控释肥研制的关键。本项目从表面含有丰富硅羟基、孔道排列高度有序、比表面积高的介孔分子筛入手，研究了助模板剂/P123摩尔比、焙烧和预聚等因素对分子筛形态结构及表面性质的影响；在获得基本包衣参数的基础上通过对包膜尿素养分释放率的测定评价了不同形貌、不同添加量和不同表面性质的分子筛对包膜材料控释性能的影响，得出了包膜材料形态结构与其性能和成膜过程的关系；选用内部不含孔道结构的纳米二氧化硅为参比粒子，进行了分子筛对聚氨酯原位反应成膜机制研究。结果表明，焙烧处理后分子筛表面的硅羟基降低，孔道中的模板剂完全脱除，且孔径增大；分子筛的形貌结构对膜材成膜过程影响不大，其微观粒径约为700 nm、添加量约为1 wt%时包膜材料的控释性能最佳，分子筛的加入可将包膜尿素控释期至少延长30天；提出了两种纳米限域粒子与基体作用机制。其一是在粒子孔内组装多元醇，然后与异氰酸酯反应的“孔约束”机制，其二是借用粒子表面硅羟基、孔内未经脱除处理的模板剂端羟基与异氰酸酯反应的“表面接枝”机制。在研期间发表了期刊论文9篇（其中SCI论文2篇、EI论文1篇），授权国家发明专利2件，申请国家发明专利3件，联合培养硕士研究生2名。该项目为新型低包膜率和高质量包膜材料的研究提供了全新思路，为化肥零增长和减施增效提供了科技支撑。