Dielectric properties of poly(vinyl chloride) in tetrahydrofuran and cyclohexanone

The dielectric absorption and dispersion of poly(vinyl chloride), M M_v = 49 000, in THF and in cyclohexanone have been studied over a frequency range of 120 kHz to 11·0 MHz, at temperatures from ?22·5 to 35°C, and at concentrations ranging from 4 to 12·0(w/v)% PVC/THF and from 2 to 8·0(w/v)% PVC/cyclohexanone. The viscosities of the two systems have also been measured at temperatures from 20 to 50°C. A single relaxation time was found (β = 0·8–1·0), which indicates that relaxation occurs by segmental rotation. The dielectric and viscous activation energies have been calculated. The dipole moment associated with the relaxation process has also been calculated. The relaxation time, dielectric and viscous activation energies and the dipole moment were found to be dependent on the type of solvent. The dipole moment also showed a molecular weight dependence. The influence of the concentration and temperature on the apparent dipole moment and on the relaxation time is discussed.     

Studies on photodegradation of poly(vinyl chloride) accelerated by α-hydroperoxy-tetrahydrofuran

A study of the role of THF, THFO₂ charge-transfer complex and α-hydroperoxy-tetrahydrofuran (HOOTHF) in the photodecomposition of poly(vinyl chloride) (PVC) film cast from THF is presented. Detailed e.s.r. studies show that during u.v. irradiation (254 nm), THF and/or HOOTHF, oxyTHF free radicals are formed, which participate in the dehydrochlorination of PVC. The final products of photooxidation of THF are α-hydroxy-tetrahydrofuran (HOTHF) and butyrolactone, which give strong i.r. absorption bands at 1735 and 1789 cm^?1, respectively. The presence of THF residues in PVC films cast from this solvent should always be considered when thermal or photochemical studies are made.     

旋风分离器内旋进涡核的PIV显示

The precessing vortex core (PVC) in a cyclone separator plays an important role in the separation performance and in further understanding of the general law of periodic unsteady flow therein. In this paper, the unsteady flow field is investigated with particle image velocimetry (PIV), and the instantaneous velocity, vorticity,tangential velocity, and radial velocity are acquired by analyzing the images of instantaneous flow. It is for the first time reported that there is a centrifugal flow region close to the dust discharge zone and its maximum value is higher than the mean radial velocity. This discovery is very important for understanding the principle of separation of particles in the area of dust discharge. Determination of the frequency and amplitude of PVC was conducted in the region where the phenomenon of PVC is remarkable. Results agree well with those obtained by hot wire anemometry. The observations of the center of “cortex core and the bimodal distribution of the amplitude of the PVC indicate the vortex core precesses around the geometric axis of the cvclone in its own way.     

Improvement of the photostabilization of PVC films in the presence of 2N‐salicylidene‐5‐(substituted)‐1,3, 4‐thiadiazole

The photostabilization of poly(vinyl chloride) (PVC) films by 2N‐salicylidene‐5‐(substituted)‐1,3,4‐thiadiazole compounds was investigated. The PVC films containing concentration of complexes 0.5% by weight were produced by the casting method from tetrahydrofuran (THF) solvent. The photostabilization activities of these compounds were determined by monitoring the carbonyl, polyene, and hydroxyl indices with irradiation time. The changes in viscosity average molecular weight of PVC with irradiation time were also tracked (using THF as a solvent). The quantum yield of the chain scission (ϕ_cs) of these complexes in PVC films was evaluated and found to range between 4.72 × 10⁻⁸ and 8.99 × 10⁻⁸. Results obtained showed that the rate of photostabilization of PVC in the presence of the additive followed the trend: According to the experimental results obtained, several mechanisms were suggested depending on the structure of the additive. Among them, UV absorption, peroxide decomposer, and radical scavenger for photostabilizer mechanisms were suggested. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Ultrasonic Study of Molecular Association of Polyethylenoxide Aqueous Solutions (A Method to Determine Molecular Weight)

Ultrasonic velocity and isoentropic compressibility measurements are reported on aqueous solutions of polyethylenoxide of different molecular weights and different concentrations using pulsed ultrasonic apparatus operating at 2 MHz and 310 K. The data obtained as a function of concentration indicate the magnitude of the contribution due to relaxation of the backbone of the ethylene group. The results show a linear increase of density, velocity and viscosity values with increasing molecular weight and concentration of PEO. In contrast, the isoentropic compressibility decreases with increasing of molecular weight and concentration of PEO. A mathematical equation correlating isoentropic compressibility and molecular weight of the polymer is suggested. This was applied to the calculation of the molecular weight of unknown samples of PEO from their measured isoentropic compressibility; the results obtained agreed well with those obtained from osmometry.     

Ultrasonic absorption and visco-relaxation study of poly(vinyl alcohol) aqueous solution. (A method for the determination of molecular weight)

Ultrasonic absorption and velocity measurements are reported on aqueous solutions of poly(vinyl alcohol) (PV-OH) of different molecular weights and concentrations obtained using a pulsed ultrasonic apparatus operating at 2 MHz and 303 K. The variations in these parameters as a function of concentration are interpreted in terms of changes in the magnitude of the contribution due to relaxation of the backbone and of the side chain acetyl groups. The results show an increase in velocity, density and viscosity with increase in molecular weight and concentration of PV-OH. In contrast the attenuation values decrease with increase in molecular weight. This suggests that interaction is occurring between PV-OH and water molecules. Deviation of the variation of the attenuation with concentration from the ‘ideal’ dilute solution behaviour at high concentration is ascribed to the effects of polymer-polymer interaction. The magnitude of the volume change associated with polymer-solvent interactions is estimated and discussed. A mathematical equation correlating the relaxation amplitude and the molecular weight of the polymer is suggested. This approach was applied to the calculation of the molecular weight of four unknown samples of PV-OH from their measured relaxation amplitudes. The results obtained agree well with those obtained from osmometry.     

溶解-沉淀-GC/MS法测定聚氯乙烯塑料中的邻苯二甲酸酯类增塑剂

建立了用溶解-沉淀-GC/MS法同时测定聚氯乙烯(PVC)塑料中15种邻苯二甲酸酯类增塑剂的分析方法。选择四氢呋喃作溶剂将PVC树脂溶解,然后用甲醇作为沉淀剂将高聚物进行沉淀,使增塑剂与高聚物进行分离而增塑剂继续留在溶液中,取清液进行气相色谱-质谱分析。本实验选择了适当的溶剂与沉淀剂,考察了聚合物分子沉淀对目标化合物的吸附作用,在优化的色谱-质谱条件下实现了15种邻苯二甲酸酯的成功分离与检测,方法平均回收率为82.7%～112.4%,测定结果的相对标准偏差为2.15%～5.77%,测定下限(S/N=10)为25～50mg/kg。该方法操作简便,精密度高,准确性好,实用性强,与国家标准GB/T22048—2008相比,检测结果基本一致,而效率大大提高。应用此方法对两种PVC塑料实际样品中的邻苯二甲酸酯进行测定,获得满意结果。     

A Study on Morphological Structure of Low Molecular Weight PVC Prepared by Vibromilling Degradation

The effects of vibromilling on particle size, crystalline structure, optical density, and the plasticizer absorption of poly(vinyl chloride) (PVC) were studied through Fourier-transform infrared spectroscopy, scanning electron microscopy and physical property tests. The experimental results show that the intensity of the FTIR absorption band at 635 cm^?1 of PVC becomes weaker and tends to disappear during vibromilling. The particle size of PVC is decreased, and the surface area and the amount of plasticizer absorption increase with increased vibromilling time. The low molecular weight PVC so prepared has lower crystallinity and glass transition temperature, and higher plasticizer absorption capacity; it should have good processability.     

Graft copolymerzation of poly(vinyl chloride) with styrene. I. Synthesis and characterization

Graft copolymerization of poly(vinyl chloride) (PVC) partially dehydrochlorinated by heating in nitrobenzene was investigated using styrene as monomer and anhydrous AlCl₃ as cationic initiator in the temperature range of 0–35°C. Effect of monomer, catalyst, and PVC concentration on % graft-on was also evaluated. Introduction of labile sites in PVC by partial dehydrochlorination in nitrobenzene resulted in an increase in % graft-on. Intrinsic viscosity of PVC–g–polystyrene in THF initially increased with an increase in % graft-on. At higher % graft-on a decrease in [η] was observed.     

Flow instability in capillary extrusion of plasticized poly(vinyl chloride)

Flow instability in a capillary extrusion is studied for a high molecular weight, plasticized poly(vinyl chloride) (PVC). The onset of melt fracture correlates with the long time relaxation ascribed to the generation and/or growth of PVC crystallites. An increase in the residence time in the cylinder leads to this long time relaxation and results in the melt fracture, although the apparent shear stress remains constant, irrespective of the residence time. The extrudate temperature and the species of the plasticizer also have a significant influence on the apparatus of the extruded products. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1277–1283, 2001     

PVC粗骨料混凝土的力学和吸能性能分析

将聚氯乙烯(PVC)软板进行粉碎得到级配良好的片状PVC颗粒以不同掺量等体积替代天然粗骨料后加入混凝土中制成试件,做单轴压缩试验和钢球自由落体冲击试验,得到立方体抗压强度、劈裂抗拉强度、卸载弹性模量和能量吸收率,用来探究不同掺量的PVC粗骨料混凝土力学和吸能性能。结果表明,随PVC粗骨料掺量增加,混凝土的抗压强度和劈裂抗拉强度均呈显著降低趋势,在实际工程中,PVC粗骨料掺量应该控制在20%左右;随PVC粗骨料掺量增加,混凝土脆性得到改善以及延性增强;混凝土的能量吸收能力随PVC粗骨料掺量增加呈显著增加趋势。     

Preparation of polyvinylchloride membranes from solvent mixture by immersion precipitation

In this study, polyvinylchloride (PVC) membranes were prepared through the immersion precipitation method using a mixture of two solvents (tetrahydrofuran (THF) and dimethyl formamide (DMF)), which had different affinities with the nonsolvent (water). Membranes prepared from PVC/THF/water system showed a sponge‐like structure with isolated pores, which were impermeable to water even at a feed pressure of 20 bars, whereas those prepared from PVC/DMF/water exhibited a porous macrovoid containing morphology with a high water flux. The precipitation time and polymer concentration profiles were calculated by using a simple mathematical model and were in good agreement with the experimental findings on PVC/THF/water and PVC/DMF/water systems. By using a mixture of DMF and THF as solvent and changing the mixed solvent composition, membranes with different morphologies from sponge‐like to macrovoid containing were obtained. The membranes showed no water flux below a DMF concentration of 50 wt % and then became increasingly permeable with increasing DMF content in the casting solution. Measurement of the system cloud points showed a linear change of system thermodynamics with variation of the mixed solvent composition. The obtained results showed that although the system thermodynamics could explain the overall behavior of the system, but the local changes such as change of membrane performance from impermeable to permeable at a certain mixed solvent composition could not be explained by the thermodynamics alone. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40206.     

旋风分离器旋进涡核的数值模拟

采用雷诺应力模型对旋风分离器内三维非稳态流场进行了模拟计算。结果表明,旋风分离器全空间内都存在旋进涡核现象。对旋进涡核现象和旋进涡核中心的运动规律进行了详细的描述,分析了不同轴向位置的旋进涡核区域内不同点的速度波动幅值和频率,得到了旋进涡核影响范围以及速度波动规律;通过分析旋进涡核中心的运动频率,得到了旋进涡核出现的强度。模拟结果与采用热线风速仪以及激光粒子成像技术(PIV)测定的实验结果基本吻合。研究结果可以分析旋进涡核对分离效率和压降的影响。     

吸水膨胀型软质聚氯乙烯/羧甲基纤维素共混物的研究

采用扫描电子显微镜等仪器测试并研究了聚氯乙烯(PVC)/羧甲基纤维素(CMC)共混物的结构与性能。结果表明:随着吸水树脂含量的增加,共混物的吸水率和体积膨胀率增大,拉伸强度和断裂伸长率降低;随着水浸泡时间的增加,拉伸强度和断裂伸长率降低;吸水后PVC/CMC共混物中CMC分散相粒径明显增大,与基体树脂界面相互作用下降。     

Study of the solvent effect on miscibility between poly(vinyl chloride) and poly(methyl methacrylate) in the solution state – viscometric measurements

In this work, the solvent effect on the miscibility between poly(vinyl chloride) (PVC) and poly(methyl methacrylate) (PMMA) in ternary polymer solutions was examined by the viscometric method. In these systems, we could understand that the used solvents, tetrahydrofuran (THF) or N,N‐dimethylformamide (DMF), mainly affect the interaction between PVC and PMMA, while prompting various miscible properties. In PVC/PMMA/THF solution, THF is a near θ‐solvent and a poor solvent for PVC and PMMA, respectively. The mixing of the tighter PMMA coils and more extended PVC coils in THF may cause the sea–island heterogeneous structure below the weight fraction of PMMA in the polymer mixture w_PMMA = 0.7, resulting in immiscible PVC/PMMA mixtures. At w_PMMA ≥ 0.7, the PVC/PMMA mixtures are relatively miscible, giving homogeneous polymer solutions. It means that the miscibility between PVC and PMMA depends on the composition of polymer mixture. However, due to the similar affinity of DMF to PVC and PMMA, PVC/PMMA/DMF solutions exhibit high miscibility between PVC and PMMA at about w_PMMA = 0.5. © 2000 Society of Chemical Industry     

High frequency ultrasonic studies of polyethylene

Ultrasonic measurements, covering the frequency range 5 MHz to 1 GHz, are reported on linear and branched polyethylene. At the lower frequencies the temperature dependence of the velocity and the amplitude of the absorption loss are consistent with observation of the familiar beta (β) and gamma (γ) relaxation processes. Studies as a function of the thermal history of the samples indicate that the detailed attenuation profile and the magnitude of the velocity are sensitive to crystallinity, reflecting changes in the branched chain content and lamella thickness. Data are also reported illustrating how the morphological changes of drawing and annealing influence the acoustic propagation parameters. The high frequency attenuation is due to the γ-macromolecular conformational relaxation, crystalline spherulite-amorphous region thermoelastic heat flow and spherulite-phonon scattering.     

Mechanical properties of oriented poly(vinyl chloride)–poly(caprolactone) blends

Blends of poly(vinyl chloride) (PVC) with polycaprolactone (PCL) of different compositions were prepared from solutions in tetrahydrofuran (THF). The dried blends were stretched at different temperatures above the glass transition, and the birefringence and mechanical properties were studied. It is shown that the birefringence of PVC and the 75/25 PVC/PCL blend follows an affine deformation scheme with a decreasing number of segments with deformation. The 50/50 PVC/PCL blend shows a complex orientation behavior because of the presence of crystallinity in the PCL phase. The mechanical properties of the blends are shown to increase with orientation, and the aggregate model is acceptably followed by the amorphous oriented blends.     

Peculiarities in the solvent absorption characteristics of epoxy‐siloxane hybrids

Epoxy‐siloxane hybrids (bi‐continuous nanocomposites) were produced from mixtures of a silane‐functionalized resin and tetra‐ethoxysilane by the sol‐gel method. Absorption of tetrahydrofuran (THF) in thin samples was found to take place by a two‐stage process, consisting of an induction period and a subsequent step‐increase to the equilibrium level. The induction time increased with increasing siloxane content, while the equilibrium amount absorbed decreased accordingly. By assuming that solvent uptake of the system follows a classical Case II absorption, a graphical relationship between induction time, diffusion coefficient, and velocity of the advanced plasticized front was proposed as a basis for the control of the solvent absorption characteristics of this type of material. Absorption of methanol (CH₃OH) took place rapidly and without an apparent induction stage, but the amount absorbed at equilibrium was much lower than for THF absorption. Increasing the siloxane content did not significantly decrease the amount of CH₃OH absorbed at equilibrium, but considerably reduced the rate of solvent uptake, while the sorption process assumed the features of a two‐stage process. The cyclic absorption of both solvents was found to cause structural changes in the epoxy network, in the form of a combination of physical aging and increased cross‐linking density. POLYM. ENG. SCI., 45:1039–1048, 2005. © 2005 Society of Plastics Engineers     

Use of mercury porosimetry for characterization of poly(vinyl chloride) suspension grades with regard to particle type,particle heterogeneity,and surface area

The correction for polymer and mercury compressibility is essential to the use of mercury porosimetry for the evaluation of the porosity of poly(vinyl chloride) (PVC) suspension granules. The polymer compressibility, however, varies with the morphology type of the granules. The technique outlined in this paper allows the appropriate correction to be made without the need for the prior determination of the polymer compressibility. Bulk-compressibility factors for the polymer samples are derived from the porosimetry data. Surface areas of PVC granules, as derived from porosimetry data using two fundamentally different techniques, are in error because of the presence of “ink-bottle” shaped pores.     

Radiation-induced polyene formation of poly(vinyl chloride). I. Effect of conformations

PVC samples with different syndiotacticities were degraded at temperatures in the range of 10° to 115°C by UV radiation. The average length of polyenes increases with increase in syndiotacticity of PVC. It was found that by comparison with the long tactic sequences, on the basis of Bernoullian statistics, the propagation reaction of the polyenes at room temperature is terminated when there are more than three racemic dyads in the tactic sequences. At room temperature, the deformation of about 1.3 Å of the PVC main chain takes place, and at temperatures above the glass transition temperature the propagation rate of the polyenes is competitive with the relaxation time between the (tt) and the (tg) conformations.