Crystallization and melting behaviors of PPC-BS/PVA blends

The isothermal crystallization and melting behaviors of poly(propylene carbonate) end-capped with benzenesulfonyl/poly (vinyl alcohol) (PPC-BS/PVA) blends over rich PVA composition range were first investigated by differential scanning calorimetry (DSC). PPS-BS/PVA interaction parameter, chi(12), calculated from equilibrium melting temperature depression was -0.44, revealing miscibility of PPC-BS with PVA in the melt and favorable interactions. The temperature dependence of crystallization rate constant at initial crystallization stage was analyzed using the modified Lauritzen-Hoffman expression. The chain width, a(0), the thickness of a monomolecular layer, b(0), the fold and lateral surface-free energies, sigma(e) and sigma, and the work of chain folding, q, for neat PVA were first reckoned to be 4.50 Angstrom, 4.78 Angstrom, 76.0 erg.cm(-2), and 4.70 kcal.mol(-1), respectively. The values of sigma(e) and q for PVA in PPC-BS/PVA blends exhibited a maximum in the neighborhood of 10/90 PPC-BS/PV, respectively.

Characterization of Full-Biodegradable Starch-PVA-Polyester Film

IntroductionConventional polymers such as polyethyleneand polypropylene persistfor many years after landdisposal.Furthermore,plastics are often soiled byfood and other biological substances,making phys-ical recycling of those materials impractical andgenerally undesirable. In contrast,biodegradablepolymers disposed in bioactive environment are de-graded by the enzymatic action of microorganismssuch as bacteria,fungi,and algae.The worldwideconsumption of biodegradable polymers increasedfrom1.4×107kg in ...

Studies on Mechanical Properties of Full-Biodegradable Starch-PVA-Polyester Films

A kind of full-biodegradable film material is discussed in this article. The film material is composed of starch, PVA, degradable polyesters(PHB, PHB-V, PCL) with built plasticizer, a cross-linking reinforcing agent and a wet strengthening agent. It contains a high percentage of starch, costs cheap and is excellent in weather fastness, temperature resistance and waterproof and it could be completely biodegraded. The present paper deals mainly with a new technical route using a new type of electromagnetic dynamic blow molding extruder and some effects on mechanical properties of the system.

Chlorohydrin water swellable rubber compatibilized by an amphiphilic craft copolymer. I. Synthesis and characterization of compatibilizer PVA-g-PBA

The graft copolymerization of butyl acrylate onto poly(vinyl alcohol) with eerie ammonium nitrate as redox initiator in a aqueous medium has been investigated. The formation of graft copolymer was confirmed by means of IR, scanning electron microscopy (SEM), and wide-angle X-ray diffraction (WAXD). The percentage of mononer conversion and percentage of grafting varied with concentrations of initiator, nitric acid, monomer, macromolecular backbone (X-n = 1750, M = 80 000), reaction temperature and reaction time. Some inorganic salts and organic solvents have a great influence upon grafting. The reaction mechanism has been explored, and rate equations for the reaction are established. (C) 2000 John Wiley & Sons, Inc.

乙基罗丹明B－磷钼杂多酸－PVA体系超高灵敏显色反应的研究

本文详细研究了乙基罗丹明Ｂ－磷钼杂多酸－ＰＶＡ超高灵敏显色反应，提出了高灵敏测量痕量磷的新的分光光度法。缔合物的最大吸收波长位于５８４ｎｍ处，其表观摩尔吸光系数为１．３×１０￣６Ｌ·ｍｏｌ￣（－１）·ｃｍ￣（－１）。并研究了缔合物的组成和红外光谱。本法直接用于钢样及试剂中痕量磷的测定，获得满意的结果，检测下限达６×１０￣（－７）％。

PREFERENTIAL SORPTION OF MODIFIED PVA MEMBRANE IN PERVAPORATION

The swelling processes of an annealed poly (vinyl alcohol) membrane, a NaOH-crosslinked poly (vinyl alcohol) membrane, a poly (vinyl alcohol)-N,N'-methylene bisacrylamide irradiation-crosslinked membrane and a poly (vinyl alcohol)/poly(AMcoAANa) blend membrane were investigated. Water was preferentially sorbed by all four membranes. The selective sorption factor alpha(s) and the selective diffusion factor alpha(d) were defined, and were used to characterize the effects of sorption and diffusion on selectivity. The results have shown that preferential sorption has a marked effect on selectivity. The mean diffusion coefficients and pervaporation properties of the four membranes are also discussed.

PVA/PVP共混体系的非等温结晶动力学

用Mandelkern和Ziabicki理论方法求得PVA及PVA/PVP共混物结晶动力学参数Z_C和动力学结晶能力G_C值,并进行了讨论。得到的Avrami指数n不随冷却速度变化,但随非晶组分PVP的加入有所减小,加入量达百分之四十以后n由3降到2;G_C值则随非晶组分的加入而增大,当PVP加入量大于百分之三十时,G_C值不再发生明显变化。同时实验表明该高聚物及其共混体系不适合于Ozawa非等温结晶动力学方程。

PVA/PVP共混物的SAXS研究

聚乙烯醇(PVA)/聚吡咯烷酮(PVP)共混物的小角X-射线散射(SAXS)研究表明,PVA/PVP共混物的结构参数与共混物组分比及热历史密切相关。按Vonk一维电子密度相关函数法,得到PVA/PVP共混物的长周期,过渡层厚随PVP组分含量增加而增加;结晶片层厚和比内表面积却随PVP含量增加而降低。热处理可提高共混物的结晶性。

PVA/PVP共混物的聚集态结构

热处理前后不同组份比二元共混物聚乙烯醇(PVA)和聚乙烯吡咯烷酮(PVP)的聚集态结构研究表明,热处理可明显提高共混物的结晶性。热处理前样品仅观察到(101)晶面衍射,热处理后可观察到4个以上衍射晶面。结晶度和微晶大小随共混物中PVP含量增加而降低。第二类晶格畸变则随PVP含量增加而增大。

超高灵敏显色反应及其应用的研究——Ⅴ.钨(Ⅴ)-SCN~--乙基罗丹明B-PVA-124体系

本文研究了在聚乙烯醇-124存在下,钨(V)-SCN~--乙基罗丹明B超高灵敏显色体系。缔合物λ_(max)=585nm,表观摩尔吸光系数ε_(585)=1.9×10~6L·mol~(-1)·cm~(-1)。钨浓度在0.1～1.5μg/25ml范围内符合比尔定律,方法曾用于水样及钢样中痕量钨的测定,结果较满意。

Effects of reflow process on the reliability of flip chip on flex interconnections using anisotropic conductive adhesives

In this paper, the effects of the solder reflow process on the reliability of anisotropic conductive film (ACF) interconnections for flip chip on flex (FCOF) applications are investigated. Experiments as well as computer modeling methods have been used. In the experiments, it was found that the contact resistance of ACF joints increased after the subsequent reflow process, and the magnitude of this increase was strongly correlated to the peak temperature of the reflow profile. Nearly 40% of the joints were opened (i.e. lifted away from the pad) after the reflow process with 260 °C peak temperature while no opening was observed when the peak temperature was 210 °C. It is believed that the CTE mismatch between the polymer particle and the adhesive matrix is the main cause of this contact degradation. It was also found that the ACF joints after the reflow process with 210 °C peak temperature showed a high ability to resist water absorption under steady state 85 °C/85%RH conditions, probably because the curing degree of the ACF was improved during the reflow process. To give a good understanding, a 3D model of an ACF joint structure was built and finite element analysis was used to predict the stress distribution in the conductive particles, adhesive matrix and metal pads during the reflow process.

Ultra-fine pitch flip-chip assembly using isotropic conductive adhesives

This paper discusses results from a highly interdisciplinary research project which investigated different packaging options for ultra-fine pitch, low temperature and low cost flip-chip assembly. Isotropic Conductive Adhesives (ICAs) are stencil printed to form the interconnects for the package. ICAs are utilized to ensure a low temperature assembly process of flip-chip copper column bumped packages. Results are presented on the structural integrity of novel electroformed stencils. ICA deposits at sub-100 micron pitch and the subsequent thermo-mechanical behaviour of the flip-chip ICA joints are analysed using numerical modelling techniques. Optimal design rules for enhanced performance and thermomechanical reliability of ICA assembled flip-chip packages are formulated.

Microwave cure of conductive adhesives for flip-chip & microsystems applications

The curing of conductive adhesives and underfills can save considerable time and offer cost benefits for the microsystems and electronics packaging industry. In contrast to conventional ovens, curing by microwave energy generates heat internally within each individual component of an assembly. The rate at which heat is generated is different for each of the components and depends on the material properties as well as the oven power and frequency. This leads to a very complex and transient thermal state, which is extremely difficult to measure experimentally. Conductive adhesives need to be raised to a minimum temperature to initiate the cross-linking of the resin polymers, whilst some advanced packaging materials currently under investigation impose a maximum temperature constraint to avoid damage. Thermal imagery equipment integrated with the microwave oven can offer some information on the thermal state but such data is based on the surface temperatures. This paper describes computational models that can simulate the internal temperatures within each component of an assembly including the critical region between the chip and substrate. The results obtained demonstrate that due to the small mass of adhesive used in the joints, the temperatures reached are highly dependent on the material properties of the adjacent chip and substrate.