负压灌溉是一种根据作物对水分的需要适时灌水的节水灌溉方式。负压灌溉系统中通常有储水水源、控压阀、负压连接管、灌水器四个部分组成，其中灌水器处于水土界面，是直接与土壤和作物根系接触的部分，对整套装置的高效运行起着至关重要的作用。前人对于负压灌溉的研究较少，对于负压灌水器的探索方面也步履缓慢，其研究领域主要集中在无机陶土陶瓷类材料，但是他们易碎、韧性差、价格较高，不适合大面积推广。
查阅文献资料发现，高分子材料中有一类微孔发泡材料，按照孔隙是否连通分为开孔型和闭孔型，而我们需要的负压渗水器材料应当是微米级别的、开孔的微孔结构。若孔径太小，渗水速率会降低，孔径过大毛管吸力作用小，无法达到较高的发泡点值。经过筛选发现一种亲水性高的微孔泡沫塑料——聚乙烯醇缩甲醛泡沫塑料（PVFM），它是由聚乙烯醇（PVA）与甲醛缩醛化而成，其柔韧性高、有可调的微孔结构、较好的渗透水性能。本试验在此基础上进一步将 PVFM 进行改良，对自行设计制备出的 PVFM 进行孔径分布、发泡点、拉伸强度、硬度、在土壤中累积入渗量、渗水速率、湿润峰运移等指标的测试，以研究不同配比、反应条件、助剂、规格对所制 PVFM负压渗水性能的影响，阐明其制备成负压渗水材料的可行性。经过研究分析，本文得到以下主要结论：
（1）原料配比对 PVFM 的性能有影响。当水比例为 8.75 时表观密度最小、吸水倍率最大。9 种不同配比的 PVFM 样品发泡点值在 26.7～73.3kPa 之间变化，且在水比例 7.50 或者甲醛比例0.75 时会达到较高水平。在-5kPa 与-10kPa 下，水比例≥7.50 的 PVFM 样品，渗水速率相对较快。PVA：水：甲醛为 1：7.50：0.75 的 5 号 PVFM 样品的平均孔径小，发泡点值为 65.3kPa，饱和导水率可达 7.45×10-4cm?s-1，理论上可以作为高性能负压渗水材料在负压灌溉中使用。
（2）反应条件对 PVFM 的性能有影响。反应温度 55℃、反应时间≥10h 时，表观密度、吸水倍率、孔隙率均有较高表现，并且三者分别在搅拌机转速 2000r?min-1、1500r?min-1、1000r?min-1时达到最高；反应温度 55℃时，或者反应时间≥10h，或搅拌机转速≤1500 r?min-1，发泡点值及对土壤的供水速率较高；综合对比分析，反应温度 55℃、反应时间 10h、搅拌机转速为 1500 r?min-1的样品，发泡点与负压下的累积入渗量同时达到较高水平，物理性能也较好，因此确定为制备负压渗水材料的最佳反应条件。
（3）不同助剂的加入对 PVFM 各性能有不同程度的影响。助剂的加入使吸水倍率下降，使发泡点、表观密度、孔隙率升高，使 PVFM 的机械性能、累积入渗量有不同程度的升高或降低。
综合看来，硅油与高岭土混合加入使表观密度和孔隙率有较大提高，对于硬度、拉伸强度、断裂伸长率也有增强，尤其对发泡点值提升最明显，对入渗量的增强上则表现一般，总体表现优于其他助剂。
（4）渗水器规格对 PVFM 渗水器的负压渗水性能有影响。空心 PVFM 渗水器的负压渗水性能优于实心，实心 PVFM 渗水器的累积入渗量与其长度负相关。15×3cm 空心 PVFM 渗水器的负压渗水性能优于陶瓷头，不同负压下，其相同时间内单位面积累积入渗量均高于陶瓷头，土壤水分运移也要快，且能控制比陶瓷头更大的土壤水分空间。在低吸力阶段 15×3cm 空心 PVFM 渗水器所确定的土壤水吸力随土壤含水量的变化关系与陶瓷头几乎一致，可以代替陶瓷头进行土壤水分特征曲线的测定。在适宜常见作物生长的-5～-10kPa 范围内，15×3cm 空心 PVFM 渗水器比陶瓷头更易满足作物对水分的需求。
关键词：聚乙烯醇缩甲醛(PVFM)，微孔材料，制备，负压渗水性能，负压灌溉
AbstractNegative pressure irrigation is a water-saving irrigation mode for timely irrigation, according to thewater needs of the crop. Negative pressure irrigation system usually consists of water storage, waterpressure control valve, negative pressure connection pipe, and emitter. Emitter is at the water-soilinterface, which directly contacts with the soil and crop root. It plays a vital role in efficient operation ofthe entire device. The former researches on the negative pressure irrigation are less, the exploration forthe emitter is slow. Their researches are mainly focused on inorganic clay or ceramic materials, whichare fragile, poor toughness, higher prices, not suitable for large area promotion.
Through cross boards researching, there is a kind of microcellular foam materials of polymermaterials. It can be divided into the open cell foam and closed cell foam according to the connectivity ofthe pores. However, the micron level and open pores are what we need. If the pore size is too small,seepage rate would be slow. If the pore size is too large, the capillary attaction would be so small thatcould not reach a higher bubble point. A kind of hydrophilicity microcellular foam plastics -- polyvinylformal foam (PVFM) was found after screening. It was made by acetalation of polyvinyl alcohol (PVA)and formaldehyde, had soft, high toughness, adjustable pore structure, and good water permeabilityperformance. In this research, PVFM was improved on this basis. Pore size distribution, bubble point,tensile strength, hardness, accumulate in the soil infiltration capacity, infiltrationrate, wetting fronttransportation were tested, so that the effects of reaction conditions, additives, specifications for PVFMcould be studied, then expounded the feasibility of making PVFM into negative permeability materials .
The main conclusions of the paper are following:
(1)The performance of PVFM could be affected by the ratio of raw materials. Apparent densityreached a minimum and water absorbency reached a maximum when H2O ratio was 8.75. Bubble pointwas largely different between, maximum of 73.3 kPa when the ratio was 1:7.50:0.50 and minimum of26.7 kPa when the ratio was 1:8.75:0.50. Generally, the bubble point could reach a high level at H2Oratio of 7.50 or formaldehyde ratio of 0.75. Under -5kPa and -10kPa, water exudation rate was higherwhen H2O ratio was larger than 7.50. In theory, the PVFM with PVA: H2O: formaldehyde ratio of1:7.50:0.75, whose mean pore size was small, bubble point was 65.3kPa, saturated hydraulicconductivity was 7.45×10-4cm?s-1, could be used as a novel negative pressure seepage material innegative pressure irrigation.
(2)PVFM performance could be affected by the reaction conditions. Apparent density, waterabsorbency, porosity had a higher performance, When the reaction temperature was 55℃, reaction timewas no less than 10h, and mixer speed was at 2000r?min-1,1500r?min-1, 1000r?min-1respectively. Bubblepoint and the rate of soil water reached a high level when the reaction temperature was 55℃, or reactiontime was no less than 10h, or mixer speed was no more than 1500 r.min-1.In summary, bubble point andcumulative infiltration would reach a high level when the reaction temperature was 55℃, reaction timewas 10h, mixer speed was1500 r?min-1,while physical performance was also excellent under these condition. So this condition could be the best reaction condition for preparing PVFM.
(3)Different additives had different effects on the performance of PVFM. On the one hand, theabsorption rate showed a decreasing trend and the bubble point, apparent density and the porosityshowed an increasing trend. On the other hand, mechanical properties and cumulative infiltration ofPVFM showed a decreasing or increasing trend in different extent. Taken together, silicone oil andkaolin together could enhance obviously the apparent density and porosity. At the same time, they couldalso improve the hardness, tensile strength and break elongation, especially bubble point. However, itwas not obvious that silicone oil and kaolin improved infiltration. In general, performance of silicone oiland kaolin was better than that of other additives.
(4)The performance of PVFM cups could be affected by physically specifications. Negativepressure seepage capacity of hollow PVFM was better than the solid. Increasing the length of solidPVFM has a negative influence on the cumulative infiltration. Negative pressure seepage capacity of15×3cm hollow PVFM were more excellence than Ceramic cup. Under various negative pressures, thecumulative infiltration per unit area of hollow PVFM cup were higher, and soil water transported muchfaster in the same time. A broader soil moisture space can be controlled by hollow PVFM cup than byCeramic cup. The moisture characteristic curve determined with PVFM cup was similar to Ceramichead. So, hollow PVFM could be used to determine soil water characteristic curve. 15×3cm hollowPVFM could more easily satisfy the crop demand for water under -5～-10kPa which was suitable forcrop growth.
Key words: Poly vinyl formal (PVFM); Microcellular materials; Preparation; Negative permeability;Negative pressure irrigation
目 录
第一章 绪论
1.1 研究背景及意义
1.2 负压渗水器概述
1.2.1 负压渗水器材料的基本特点
1.2.2 负压渗水器的作用原理
1.2.3 负压渗水材料的研究进展
1.3 高分子材料简介
1.3.1 微孔发泡高分子材料概念及特性
1.3.2 微孔发泡高分子材料研究进展
1.4 PVFM 材料简介及研究进展
1.4.1 PVFM 简介
1.4.2 PVFM 研究进展
1.4.3 PVFM 制备的影响因素
1.5 研究契机
1.6 研究目标
1.7 研究内容
1.8 技术路线
第二章 材料与方法
2.1 PVFM 材料的制备
2.1.1 试剂与仪器
2.1.2 样品制备
2.1.3 测试与表征
2.2 对渗水器供水性能的测试——土柱实验
2.2.1 供试土壤
2.2.2 不同负压下累积入渗量、渗水速率、土壤含水量的测定
2.2.3 不同负压下湿润峰的观测
第三章 原料配比对 PVFM 负压渗水性能的影响
3.1 试验设计
3.2 结果与分析
3.2.1 配比对 PVFM 样品外观质量的影响
3.2.2 配比对 PVFM 样品基本物理性能的影响
3.2.3 配比对 PVFM 样品孔隙结构的影响
3.3 讨论
3.4 小结
第四章 不同反应条件对 PVFM 负压渗水性能的影响
4.1 试验设计
4.2 结果分析
4.2.1 不同反应条件对表观密度、吸水倍率、孔隙率的影响
4.2.2 不同反应条件对发泡点及供水速率的影响
4.2.3 不同反应条件下四种 PVFM 样品性能的比较
4.3 讨论
4.4 小结
第五章 不同助剂对 PVFM 负压渗水性能的影响
5.1 试验设计
5.2 结果分析
5.2.1 不同助剂对 PVFM 基本物理性能的影响
5.2.2 不同助剂对 PVFM 机械性能的影响
5.2.3 不同助剂对 PVFM 负压渗水性能的影响
5.3 讨论
5.4 小结
第六章 物理规格对 PVFM 负压渗水性能的影响
6.1 试验设计
6.1.1 参与实验的渗水器规格
6.1.2 观测项目
6.2 结果分析
6.2.1 一维条件下 PVFM 渗水器与陶瓷头渗水性能的比较
6.2.2 三维条件下较优 PVFM 与陶瓷头在不同负压下的湿润峰运移状况
6.3 讨论
6.4 小结
第七章 全文总结与展望
7.1 全文主要结论
7.2 创新点
7.3 展望
参考文献
附 录
致 谢
