可调节土壤湿度的导水纤维功能薄膜的研究

通过聚乙烯醇和超细层状无机材料以不同比例混合对植物纤维做涂层化处理,借助显微照片分析了涂层与纤维及纤维与基体的复合;利用示差扫描量热法和热重法分析了涂层比例对纤维表面吸附水的影响;测量了膜材包装水后在失水率随温度和湿度的变化;通过应用蓄水渗膜包装水现场造林,统计了造林成活率.结果表明:导水纤维经涂层处理后可实现与环境友好高分子基材的浸润结合;通过调整导水纤维涂层中的聚乙烯醇与片层无机物混合比例,可实现不同的渗水速度;蓄水渗膜材料能够根据土壤的温度和湿度变化调节渗水速度,从而可以根据需要调整土壤含水量;应用蓄水渗膜材料造林的树苗成活率比对照林高出20%～50%,生长量也有明显优势.     

蓄水渗膜导水纤维的研制

选取植物纤维、动物纤维和化学纤维分别与环境友好性高分子复合成膜进行包装水渗水试验,初步选取了植物纤维作为蓄水渗膜导水纤维材料.为了提高植物纤维的导水性能,制膜前对其进行预处理,在常温、50、100℃温度下分别用不同浓度的自制预处理剂浸泡处理后,观察纤维的微观形貌和测量纤维的拉伸性能,发现在常温下预处理剂的浓度为14%时纤维的亲水性及拉伸性提高,微观形貌好,常温下使用14%的预处理剂浸渍30min后制备的纤维可作为蓄水渗膜的导水纤维.     

可控缓释水的功能导水涂层纤维制备及其渗水特性分析

针对荒漠化地区生态恢复难题,将吸水性有机树形高分子与超细蒙脱石颗粒混合成胶体,涂敷于天然植物纤维表面,制备出一种具有可控缓释水功能的导水涂层纤维,并与环境友好性材料复合成膜.采用热重法分析了涂层材料吸-脱附水特性、快速水分测定法测量了膜材包装水后失水率随温度和土壤湿度的变化,利用环境扫描电镜观察了涂层纤维表面形貌、分析了涂层纤维的动态水分运移机理,统计出膜材包装水现场造林后的土壤含水量.实验结果表明,这种功能导水涂层纤维能够实现不同涂层组分下渗水速度的可设计性和基于土壤温度及湿度的自调节机制,保证了植物生长的合理土壤湿度.     

层状黏土材料对导水纤维涂层脱附水性能的影响

涂层导水纤维是导水纤维复合薄膜材料的实现水分子可控缓释的关键,涂层材料中的添加剂选用层状黏土.本工作通过比较不同涂层导水纤维的渗水规律,研究了普通黏土、高岭土、膨润土三种黏土添加剂对导水纤维涂层脱附水性能的影响.实验采用Perkin Elmer Diamond SⅡ综合热分析仪、Cambridge Instrucment STEREOSCAN360扫描电镜、M30快速水分测定仪等检测设备,研究了不同涂层导水纤维的结构和持水能力以及涂层导水纤维的吸附和脱附水分子的规律.实验结果表明这三种黏土都能实现涂层导水纤维对水分子的可控缓释性,其中添加剂T(普通黏土)处理的涂层导水纤维在实现分子传水可控性上要优于其他两者.     

粉煤灰涂层材料的控释水特性

提出了一种新型涂层导水纤维的制备方法.用粉煤灰和有机溶剂溶解的EVA混合做涂层材料,选用与膜材成分相同的聚乙烯纤维作为预涂层纤维基体.用比表面积分析仪表征粉煤灰的孔径分布,在环境扫描电子显微镜下观察纤维表面微观真实形貌,用快速水分测定仪测试纤维在不同温度下的连续失水情况.改变土壤的相对含水量,测定了优选配比涂层纤维的失水.结果表明:EVA含量最少的纤维涂层渗水效果最好,涂层纤维的保水功能是由于粉煤灰的多孔产生了毛细孔凝聚现象,该涂层导水纤维对温度以及土壤湿度都具有自调节功能.     

蒙脱土/聚丙烯酰胺复合涂层导水纤维的制备及性能

用钠基蒙脱土/聚丙烯酰胺及有机蒙脱土/聚丙烯酰胺两种复合涂层材料,对天然纤维进行涂层化处理,制备了两种蒙脱土/聚丙烯酰胺复合涂层导水纤维.用快速水分测定法研究了导水纤维在不同温度和土壤湿度时的动态导水规律.利用扫描电镜观察了涂层纤维的表面形貌及涂层材料在不同水势下的微观形貌.采用X射线衍射仪及比表面积与孔径分布测定仪对普通蒙脱土与有机蒙脱土的物理结构进行表征.实验表明涂层导水纤维具有基于土壤温度及湿度的自调节机制,以便保证植物生长的合理土壤湿度.对蒙脱土进行有机化处理后,其层间距及孔径增大,有利于水分的传导.     

自调节土壤湿度的水分子控释复合导水材料

用聚丙烯酰胺和超细钠基蒙脱石制备了一种用于荒漠化地区节水造林的水分子渗灌复合导水材料。该材料采用分子渗水的方式进行供水,大大节省了水资源,实现了水分的最有效利用。采用红外光谱方法研究了复合材料的官能团变化;采用SEM和ESEM分析了材料的微观结构和不同水势下的动态行为;通过不同温度/湿度下的失水率/含水率试验得到了材料在外界条件变化下的导水规律,最后对复合导水涂层材料的动态导水机理进行了分析和讨论。结果表明:复合材料的导水速率随着材料中蒙脱石含量的增加而增大,通过调节蒙脱石与聚丙烯酰胺的配比可调整材料的导水速度。材料的导水速度随外界温度的升高而增大,随着外界湿度的增加而减小。导水涂层材料的导水机制与水势及水势梯度密切相关。在高水势下,蒙脱石颗粒断桥,水分由聚丙烯酰胺传导,导水速度慢;在低水势下,蒙脱石颗粒桥接,水分经蒙脱石颗粒间的导水通道传导,导水速度快。沿着导水涂层纤维,形成了水势梯度差,水分从高水势向低水势进行自发传导。     

功能导水涂层纤维的可控缓释水机制研究

将吸水性有机高分子PVA与超细蒙脱石颗粒混合成胶体,涂敷于天然植物纤维表面,制备出一种具有可控缓释水功能的导水涂层纤维.利用环境扫描电镜观察涂层纤维表面形貌,采用热重法分析涂层材料吸-脱附水特性,采用快速水分测定仪测量了膜材包装水后失水率和土壤湿度的关系,分析涂层纤维的动态水分运移机制.实验结果表明,蒙脱石颗粒充分分散在PVA胶体网络间隙,纤维水势高的一端PVA溶胀,蒙脱石颗粒发生断桥,水分运移依靠PVA吸-脱附作用;纤维水势低的一端PVA脱水,蒙脱石颗粒桥接形成传水通道.由此实现了由分子传水和层间传水能垒不一致导致的沿纤维纵向水势梯度变化而形成的水分运移的过程机制.     

动态自调节导水复合涂层的过程行为及应用

制备了一种用于荒漠化治理中节水造林的动态导水复合材料.该材料是由不同比例的高吸水性树脂与蒙脱土复合于纤维支撑体表面构成涂层.用SEM分析了涂层材料的显微结构,用热分析研究了材料的吸脱附水特性,用快速水分仪测定了不同土壤湿度条件下材料的导水参数.结果表明:蒙脱土颗粒能够拆解并分散于高吸水树脂的枝状体结构中;通过树脂对蒙脱土的支配作用所产生的蒙脱土颗粒的空间连续性来确定其导水速率,该速率随土壤湿度的降低而增加;使用该材料后云杉树苗成活率得以大幅度提高;涂层材料对土壤湿度的自调节作用为植物生长提供了合理的水分条件.     

原生粉煤灰涂层导水纤维的制备及其渗水特性试验研究

利用粉煤灰和有机溶剂溶解的EVA混合在聚乙烯纤维基体上涂层,制备新型涂层导水纤维.试验采用比表面积分析仪、环境扫描电子显微镜、快速水分测定仪分别对纤维涂层形貌以及渗水特性进行表征.试验结果表明:在筛选后的比例中,EVA 含量最少的纤维涂层渗水效果最好;该涂层导水纤维对温度以及土壤湿度都具有自调节功能.     

涂层及热处理状态对碳纤维机械性能的影响

本文系统研究了热处理对具有Ni、SiC、SiC-Ni双涂层的碳纤维机械性能的影响。结果表明,碳纤维拉伸强度随SiC涂层厚度增加而提高,涂SiC碳纤维断裂方式为纤维拔出型。经热处理后涂SiC碳纤维性能不下降。涂SiC-Ni碳纤维随热处理时间延长而缓慢下降,涂Ni碳纤维性能下降最快。分析了碳纤维性能下降的原因及碳纤维在不同条件下的断裂机制。     

Some hygrothermal effects on the mechanical behaviour and fractography of glass-epoxy composites with modified interface

The mechanical behaviour of glass fibre-reinforced epoxy composites with introduced layers of materials and with fibre coating is studied. The role of aerosil powder as a filler material is investigated, and the fracture mode is analysed by scanning electron microscopy. The investigation shows a considerable drop in interlaminar shear stress for the higher fibre volume fraction, whereas the introduction of filler materials to the composite causes no change. Surface mat-reinforced samples show a marginal increase in shear stress. Exposure to moisture reduces the interlaminar shear stress value faster for the higher fibre volume fraction, thereby highlighting the role of the interfacial area. Impact values for coated and uncoated fibres show an identical trend with exposure to dry heat, the former always recording lower values. The impact value decreases faster with moisture absorption for the composite with the higher fibre content. Fractography reveals poor adhesion in the coated laminates.     

Moisture absorption,tensile strength and microstructure evolution of short jute fiber/polylactide composite in hygrothermal environment

In this research, aging behaviors of short jute fiber/Polylactide (PLA) composite material in hygrothermal environment were investigated. The material was fabricated by using film stacking hot pressed method. The aging was carried out for uncoated samples and adhesive tape coated samples in saturated vapor at 70 °C. Moisture absorption rates of the samples were measured during the aging process. It is found that the moisture absorption process of uncoated samples includes three stages: a short and quick moisture uptaking stage, a slow stable uptaking stage and an abrupt very quick moisture uptaking stage. Microstructures of the samples in different aging stages were observed. The main defects occurred during the aging process include pores, microcracks, delamination and complete relaxation in the whole structure. The results reveal that the moisture absorption and aging process can be effectively retarded by coating. The molecular weight measurement by gel permission chromatography (GPC) indicated that the PLA matrix was severely degraded in hygrothermal environment. Tensile strength severely decreased after aging.     

SiC-Ni 双涂层的界面反应对 C/Al 复合材料力学性能的影响

研究了不同工艺条件下具有 SiC-Ni 双涂层的碳纤维增强 Al 基复合材料的界面反应、界面结构及其对复合材料力学性能的影响,分析了不同界面条件下复合材料的典型破坏过程。实验表明:以 SiC 涂层作为界面反应阻挡层,可有效地阻止纤维与基体的反应,保证 C/Al 复合材料在界面反应很严重的情况下仍能保持较高的强度水平。初步提出了这种复合材料保持较高强度的原因和断裂机制。     

Simple model for consolidation of metal matrix coated SiC fibre composites

Abstract

A simple approach to modelling the consolidation of matrix coated fibre composites is presented. It employs an existing porous material constitutive model for monolithic materials. It is argued that in the consolidation of metal coated SiC fibres, the deformation primarily occurs in an outer layer of the fibre coating, and the internal core remains undeformed, largely because of the generally hydrostatic compressive loading, and because of the incompressible nature of the material in creep. The consolidation process is therefore not vastly different to that occurs for monolithic metal fibres, and similar equations can therefore be used for the composite consolidation. The constitutive equations have been implemented into general purpose non-linear finite element software within a large deformation formulation by means of two different user subroutines, one providing a general implementation, and the other a cpu time efficient approach. The manufacture and testing of SiC continuous fibre, Ti-6Al-4V metal matrix composite specimens is described and the results of the tests compared with the model calculations, showing that good agreement can be achieved with a simple model. The dependence of volume fraction of fibres and temperature can be introduced empirically through the specification of just two material constants. The model is therefore useful in the development of consolidation processes.     

Effect of Aqueous Film Coating Conditions on Water Removal Efficiency and Physical Properties of Coated Tablet Cores Containing Superdisintegrants

Few studies have examined the effect of aqueous film coating process conditions on the physical integrity of the final coated product. Characterization of the aqueous film coating process was previously carried out by selecting water removal efficiency as the response variable to detect and monitor moisture accumulation in the tablet bed [1]. In this study, regression techniques were utilized to obtain the relationship between some physical characteristics of aqueous film coated tablet cores that contained superdisintegrant and several process parameters such as inlet air temperature, spray rate, and pan speed. Tablet response variables measured included residual moisture content, tensile strength and percent porosity. Predicted values of these properties were plotted as a function of the inlet air temperature and the coating solution spray rate. The correlations between the coated tablet response variables and the water removal efficiency of the coating process indicated that coated tablet properties such as residual moisture content, tensile strength, and porosity were linearly correlated with the water removal efficiency of the coating process, which is indicative of the environmental coating conditions present in the coating pan.     

Chemical vapor deposition of titanium nitride on carbon fibres as a protective layer in metal matrix composites

The significance of carbon fibres for reinforcing metals has increased in the last years, because of their excellent mechanical properties. However, to avoid the weakening reaction during MMC fabrication between the fibre and the liquid metal, a protective coating has to be applied. Continuous carbon fibre roving with 6000 filaments were coated with TiN by thermal induced chemical vapour deposition (CVD) using a gas mixture of TiCl₄, N₂ and H₂ as a precursor. The deposition process in the reactor was simulated by a modified Phoenics-CVD software program using a 2D-axisymmetric model. Carbon fibres reinforced magnesium matrix composites are fabricated by a pressure infiltration casting process. The mechanical properties of the MMCs can be used to demonstrate the efficacy of the coated fibre approach. The rule of mixture is realized to 98% for the coated fibre, and only 48% for the uncoated system. The infiltration pressure during the processing of composites was lowered from 10 to 1 MPa for the TiN coated system.