聚乙烯包膜肥料控释膜层结构特征研究

Morphological structure and pore property of polyethylene controlled-release film sprayed on urea

【目的】包膜肥料控释膜层结构和孔隙性质直接影响其养分释放速率。研究包膜肥料膜层结构特征,可以明确膜层结构参数与养分释放速率的关系,揭示包膜肥料控释机制,为建立养分释放数理模型提供理论依据。【方法】以聚乙烯包膜肥料控释膜层作为研究对象,量化研究了聚乙烯喷涂控释膜层的结构特征参数。利用扫描电镜,观测了在不同放大倍数下,采用喷涂工艺制备的聚乙烯包膜肥料膜层的外表层、横断面和内表层特征;以压汞仪测定了膜上孔隙的大小和分布;采用泡点法研究了大孔隙的最大孔径。【结果】不同放大倍数下的扫描电镜观测结果表明,喷涂法制备的包膜肥料控释膜层外表面整体上光滑、平整、均匀、疏松,但局部存在少量孔隙,孔径主要分布在1000~50 nm的范围内;在放大倍数很高的情况下,整体上膜层无细微孔隙结构。控释膜层厚度约为60~100μm,断面形貌疏松无孔。膜层内表面粗糙,高低起伏不平、犬牙交错。膜壳材料堆密度为0.4~0.8 g/mL,低于聚乙烯密度,属于疏松结构。孔隙结构分析结果表明,聚乙烯控释膜层的中值孔径为4.5~5.3 nm,与对比的聚乙烯薄膜基本一致,说明两种膜分子链间的细微结构没有差异;但是聚乙烯控释膜层中存在占比18%的直径约为1000~50 nm的较大孔,孔径小于10 nm的间隙占82%,进一步说明占比少的大孔影响控释膜层释放性能。喷涂控释膜层总孔体积在0.4686~1.2260 mL/g,平均孔径在25.1~86.8 nm范围内,孔隙率为33.0%~50.6%,显著高于拉伸工艺制备的聚乙烯薄膜。释放期在1~6个月的包膜控释肥料,最大孔径在990~480 nm的范围,随包膜肥料释放期的增加,膜孔直径逐步减小,说明包膜控释肥料养分释放速率与其最大孔径存在内在联系。【结论】综合3种方法的测定结果,聚乙烯控释膜层可以看作是膜层均匀致密且局部有孔隙,膜壳直径3 mm,膜层厚度约为50μm,最大孔径为1μm,平均孔径为50 nm的密闭球形壳体。最大孔是水分和养分进出膜层的主要通道,决定了包膜肥料养分释放速率的快慢。

【Objectives】The morphology and pore properties of the controlled-release film directly affect the nutrient release rate of polyethylene(PE)-coated fertilizer.The study on them will help predicting the relationship between the structure parameters of PE films and nutrient release rate of a coated fertilizer more precisely.【Methods】Polyethylene coating fertilizer samples were all prepared by spraying process in the study.The surface morphology,pore structure and maximum membrane pore sizes of the obtained controlled-release fertilizers(CRFs)were quantitatively measured using scanning electron microscopy,mercury porosimeter and water immersion method.【Results】The films of CRFs were smooth,uniform and loose,a few of holes were observed,which were mainly distributed in the range of 1000–50 nm.The thickness of the controlled-release film was about 60–100μm,and the inner surface of the film was rough.The total pore volume of the film was in range of 0.4686–1.2260 mL/g,and the average pore diameter was in range of 25.1–86.8 nm,the porosity rate was in range of 33.0%–50.6%,and the structure was loose.The maximum pore size of CRFs ranged from 990 to 480 nm with a release period of 1 to 6 months.【Conclusions】Comprehensively considering the results from the three measurement methods,the controlled-release PE film is generally an even and closed spherical shell,and about 50 microns in thickness.The membrane is roughly continuous and evenly compact with diameter of 3 mm.However,there are pores of average 50 nm in the partial position,and the maximum pore is about 1μm.The maximum pores are the main pass of water and nutrient,determining the release rate of nutrients in the CRFs.