聚烯烃包膜控释肥膜层孔径测定方法研究

【目的】物理包覆法制备的聚合物控释膜层结构直接决定了其养分的释放,控释膜层存在的微孔和裂缝是肥芯养分进出的最主要通道。因此,控释膜层结构特征是决定包膜肥料释放性能的关键因素。泡点法能够准确测定膜的有效孔径及其分布,是一种重要的膜层孔径测试方法。本研究根据包膜肥控释膜层的特点,研究适用于测定聚烯烃包膜控释肥膜层最大孔径的泡点法,并建立测定包膜肥料最大孔径的标准方法。【方法】以泡点法为基础,建立测定膜层最大孔径的装置,确定膜层最大孔径的位置,并利用扫描电镜对膜层的孔隙结构进行观察,确定其形貌结构特征;通过对浸润剂种类、 浸润时间、 浸润温度等测定因素的比较分析,确定适合测定膜层最大孔径的最佳条件;并以释放期分别为1、 3、 5、 6月的聚烯烃包膜肥料为研究对象,研究释放期与最大孔径之间的相关关系。【结果】 1)将4种肥料放入水中浸泡,随浸泡时间的增长,膜层表面有尿素结晶的白色点位的颗粒逐渐增多,浸泡10天,80%以上颗粒均能检测到泡点,其白色点位可被认为是肥芯养分的溶出通道,以颗粒的白色点位作为膜层最大孔径的测定位置;这与扫描电镜观察到的孔隙或孔洞的特征相吻合 ;2)通过对浸润条件研究,认为在25℃,以Q-16为浸润剂,浸润5 min能够使用自制的压泡法装置直接测定控释膜层最大孔径; 3)释放期为46、 105、 160、 198天的包膜肥料的膜层平均孔径分别为1.93、 0.58、 0.45和0.41 m,最大孔径随着释放期的缩短而增大,随着微分溶出率的增加而增大,最大孔径与释放性能存在密切联系。【结论】综上所述,采用塑料管端封装浸泡10天的膜层,以Q-16作为浸润剂,在室温下浸润5 min的条件下可以测定最大孔隙结构,泡点法可作为一种标准方法用于控释膜层最大孔径的测定,其测定的最大孔径与释放期存在相关关系,对包膜控释肥控释性能和养分释放机理的深入认识有重要作用。

Study on measuring methods for pore size of polyolefin film coated controlled-release fertilizer

【Objectives】 Structure of controlled-release film of polymer, prepared by physical covering methods, directly determines the mass transfer of nutrients. The main channel for the release of nutrients is the micropores and cracks in the films. Bubble point method is widely employed for measuring the diameter and their distribution of available pores in the films. In this study, the method was modified for the determination of the maximum aperture in the polyolefin films, which is used for coating of fertilizer, and the parameters for establishing a standard method were testified.【Methods】 On the base of the bubble point method, a device for the determination of maximum pore diameter of the film were installed, and the location of maximum aperture in the film was determined. The morphology and structural characteristics of pores on the film was observed by scanning electron microscope. The optimum parameters for the modified method were determined by the comparative analysis of different infiltration agents, temperatures and time. The correlation between the releasing period and the maximum pore was studied using polyolefin coated fertilizer with releasing periods of 1, 3, 5 and 6 months.【Results】 1)After the four types of fertilizers were soaked into water, the granules with urea crystallization of white point in the film surface are gradually increased with the elongation of the soaking. The white points could be thought as the releasing channel of fertilizer core nutrients. The white points of granule are set as the position for the determination of the maximum aperture film. At the 10th day of soaking, the bubble point could be detected in more than 80% of the granules. The characteristics of these pores or holes are matched with those observed by scanning electron microscope. 2)The maximum pores of the film are determined directly by the pressure bubble method with self-made apparatus at temperature of 25℃, Q-16 is selected as wetting agents and soaked for 5 min. 3)The average pore sizes of the coated fertilizer with releasing periods of 46, 105, 160 and 198 d are 1.93, 0.58, 0.45 and 0.41 m, respectively. The maximum pore sizes are increased with the shortening of releasing period and increasing of nutrients. Therefore, a close relationship exists between the maximum pore size and the release performance. 【Conclusions】 The bubble point method can be used as a standard method for the determination of maximum pore diameter, there is relationship between the determination of maximum aperture and the release time, it plays an important role in further understanding the controlled release performance and coated controlled release mechanism of fertilizer.