Studies on preparation of HDPE/CB composites including a novel oriented structure by the microwave heating and their characterization

Microwave heating has several advantages over traditional methods of heating, including rapid and uniform heating, greater penetration depth of heat into material, lower power costs and selective heating within the material and so on. In this paper, effects of microwave heating on the properties of high‐density polyethylene/carbon black (HDPE/CB) composites were studied. The results show that the HDPE/CB composites can be heated via microwave irradiation, and composites with different CB concentration exhibit different microwave heatability. The 20 wt% CB composites have the most rapid heating rate, and its temperature reaches 78°C after 10 sec, and 159°C after 150 sec, respectively. Meanwhile, microwave heating improves the mechanical properties of HDPE/CB composites. Scanning Electron Microscopy (SEM) analysis shows a better combination between CB particles and HDPE after microwave irradiation. Furthermore, selective heating of microwave was used to prepare a novel oriented structure, which the core layer has preferential orientation and the surface layer has little orientation. Characterization of the novel oriented structure was also studied. Wide angle X‐ray diffraction (WAXD) analysis of 25 wt% CB composites with the novel oriented structure shows that the diffraction peaks of the surface layer are obviously weaker than those of the core layer, which indicates that orientation in the core layer is more intensive than that in the surface layer. The novel oriented structure is different to the traditional skin‐core structure, in which the surface layer has preferential orientation and the core layer has little orientation. Copyright © 2009 John Wiley & Sons, Ltd.     

微波辐照实现PVC-PS之间的Friedel-Crafts接枝反应

在四氢呋喃、环己酮等溶液中实现了聚氯乙烯(PVC)与聚苯乙烯(PS)的Friedel-Crafts接枝反应,考察了加热方式、反应温度、催化剂种类、催化剂用量对接枝反应的影响,通过FTIR表征了PVC-g-PS接枝物的结构,探讨了反应的机理和特点.研究发现,油浴加热和微波辐照都能使PVC和PS发生接枝反应,但微波辐照效果更好,油浴加热,接枝率仅0.27%,而微波辐照接枝率高达23%;油浴加热时产物少且多为间位,微波辐照时产物多且多为对位和邻位.无水AlCl3、无水FeCl3、无水SnCl4皆对PVC与PS之间的Friedel-Crafts反应具有催化活性,其中无水AlCl3的催化活性最高,其最佳用量为质量分数3%,此时,接枝率达到29%.当无水AlCl3过高时,PVC降解,产生双键,接枝率下降.表明微波辐照是实现PVC与PS之间Friedel-Crafts接枝反应的有效途径.     

Poly(vinyl chloride) Nanocomposites

Poly(vinyl chloride) is one of the major thermoplastics beside other commodities polymers like polyethylene and polystyrene. However, some of its main characteristics such as plasticity, thermal and photo stability are inferior to other commodity polymers. Adding nano scale inorganic fillers to poly(vinyl chloride) or other polymers in view to obtain polymer nanocomposites with superior properties has drawn the attention of many researchers in the last decades. Poly(vinyl chloride) nanocomposites are obtained mainly by in situ polymerization, solution based or mixing techniques. The resulting products show improvement of most important properties of poly(vinyl chloride) such as thermal, mechanical, rheological, flammability, antibacterial, etc. This paper presents preparation ways of poly(vinyl chloride) nanocomposites using different nano fillers and the improved properties compared with those of virgin poly(vinyl chloride).     

IR laser ablation of poly(vinyl chloride): Formation of monomer and deposition of nanofibres of chlorinated polyhydrocarbon

IR laser-induced ablation of poly(vinyl chloride) was examined under different irradiation conditions and its volatile and solid products were characterized by mass, infrared, UV and X-ray photoelectron spectroscopy, electron microscopy and thermogravimetry. It is demonstrated that the major component among the volatile products is monomeric vinyl chloride and that the process causes deposition of Cl-containing polymeric films. The proportion between the volatile and solid products as well as the nature of the deposited films at different laser fluences have been examined. We show that the deposited films incorporate less Cl atoms than poly(vinyl chloride) and that they initially contain conjugated CC bonds and incorporate nano-sized fibre and necklace features. The process represents the first example of thermal degradation of poly(vinyl chloride) into monomer and makes it possible to fabricate crosslinked Cl-containing intractable polymer films.     

WASTE LEATHER PARTICLES AS A FILLER FOR POLY(VINYL CHLORIDE) PLASTISOLS

Waste leather granules were incorporated into poly(vinyl chloride) plastisols containing di-octyl phthalate as plasticizer. The rheological behavior and gelling characteristics of plastisols were investigated and the filled samples were tested for their physicomechnical properties. It was found that density, wear resistance and Shore D hardness of composites increase whereas the tensile properties are considerably deteriorated with the incorporation of leather. In order to improve mechanical properties, treatment of the leather granules was applied with a solution of ethylene vinyl acetate (EVA) copolymer. This seemed to produce a coating that promotes adhesion as well as proper wetting of the granules and, thus, significantly improves the tensile characteristics of specimens. The upper level of leather content, in order to produce filled products with acceptable properties, was estimated at the concentration of 50 phr. This is an extension to the limits of the system plasticized poly(vinyl chloride)/leather determined in the case of its processing via melt mixing techniques.     

IR laser-induced decomposition of poly(vinyl chloride-co-vinyl acetate): Control of products by irradiation conditions

IR laser-induced, ablative decomposition of poly(vinyl chloride-co-vinyl acetate) was examined under different irradiation conditions and its volatile and solid products were characterized by mass spectroscopy, infrared spectroscopy, Raman spectroscopy and UV spectroscopy and EDX-measurements. The laser decomposition of the copolymer, compared with that of poly(vinyl acetate) and poly(vinyl chloride), is revealed to be a more efficient process leading to solid films with the proportion of Cl- and CH₃C(O)O-groups controlled by irradiation conditions.     

Microwave-Assisted Synthesis of Poly(ε-caprolactone)-block-poly(ethylene glycol) and Poly(lactide)-block-poly(ethylene glycol)

Summary: This study reported the preparation and characterization of PCL-b-mPEG (poly(ε-caprolactone)-block-poly(ethylene glycol)) and PLL-b-mPEG (poly(L-lactide)-block-poly(ethylene glycol)) diblock copolymers by microwave heating and comparison of resulted products the ones with prepared by conventional heating. Diblock copolymers were synthesized successfully by the microwave-assisted ROP in the presence of stannous octoate (SnOct₂) as catalyst under nitrogen atmosphere in different monomer ratios. Structural and functional characterization of copolymers were performed by FTIR, ¹H-NMR and DSC. Molecular weight values were determined by GPC and also calculated from ¹H-NMR. According to the results, microwave irradiation allowed to obtain polymers with very narrow size distribution in very short reaction time. Similar polymers prepared by conventional heating were also synthesized for comparison. Molecular weight and conversion of polymers were increased by irradiation time. This change was continued until a certain time point after which no more increase was observed. It was concluded that microwave irradiation is a succesful method to obtain these diblock copolymers in very short reaction time and with a similar conversion obtained by conventional method.     

Preparation and Characterization of Quaternized Chitosan Under Microwave Irradiation

For the first time, N-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (HTCC) was prepared through a fast, easy and efficient method with the assistance of microwave irradiation, and the quaternized chitosan was also degraded via the microwave irradiation. A comparative study was performed by using the conventional heating method to prepare HTCC. The structure and property of the quaternized chitosan obtained by these two methods were characterized by GPC, XRD, FTIR, NMR, TG and elemental analysis. It was shown that quaternized chitosan was successfully prepared within 50 min via microwave irradiation method, while a much longer time of 6–7 h was needed with the conventional heating method. The substitutions both occurred on the C2 position of chitosan with the two different methods, and their HTCC products had weight average similar molecular weight (Mw), structure and thermal stability. The HTCC prepared by the microwave irradiation method had a little lower degree of substitution (DS) than those prepared via conventional heating with the same mole ratio (6:1) of the intermediate to chitosan. The degradation study showed that the Mw of HTCC decreased rapidly from 4.6 × 10⁵ to 1.1 × 10⁵ in 1 h under microwave irradiation, while it only decreased from 4.6 × 10⁵ to 2.1 × 10⁵in 1 h through conventional heating degradation. These results revealed that microwave irradiation is a more efficient and environment-friendly way to obtain the water-soluble chitosan derivatives and their degraded products.     

Grafting of Polymers Having Pendant Peroxycarbonate Groups Onto Carbon Black and Postpolymerization of Vinyl Monomers

Abstract

Postpolymerization of vinyl monomers initiated by pendant peroxycarbonate groups of grafted polymer chains on carbon black (CB) was investigated. The grafting of polymers having pendant peroxycarbonate groups onto CB was achieved by the trapping of polymer radicals formed by the thermal decomposition of copolymers of t-butylperoxy-2-methacryloyloxyethyl-carbonate (HEPO) with vinyl monomers such as vinyl acetate (VAc), styrene (St) and methyl methacrylate (MMA). The copolymers having pendant peroxycarbonate groups were prepared by copolym-erization of HEPO with vinyl monomers using azo initiator under irradiation of UV light at room temperature. The amount of remaining pendant peroxycarbonate groups of the poly(VAc-co-HEPO)-grafted CB obtained from the reaction at 90°C was maximum and decreased above the temperature. Furthermore, the postpolymerization of vinyl monomers, such as St, MMA, and VAc was initiated in the presence of poly(VAc-co-HEPO)-grafted and poly(St-co-HEPO)-grafted CB and the corresponding polymers were postgrafted onto CB to give branched polymer-grafted CB. The percentage of poly(St)-postgrafting (proportion of post-grafted poly(St) to poly(MMA-co-HEPO)-grafted CB used) increased with increasing polymerization time, but became constant at 20% after 4 hours.     

Dechlorination of poly(vinyl chloride) by microwave irradiation I: A simple examination using a commercial microwave oven

Poly(vinyl chloride) (PVC) was decomposed by microwave (MW) irradiation (2.45 GHz) using a commercial MW oven. The efficiency of dielectric absorption was evaluated quantitatively from the rate of temperature increase on MW irradiation. The efficiency of dielectric heating increased at temperatures above the glass transition temperature (T_g). The decomposition on MW irradiation, monitored using the weight, depended on the initial (preheating) temperature of the sample before irradiation. The degradation time profile with various initial temperatures was shifted along the time axis and was successfully superimposed on a single curve. A pure PVC film was subjected to heating at a constant temperature from 230 °C to 310 °C, and the rate of weight decrease on heating was measured. The apparent activation energy was 84.4 kJ/mol for a single monomer unit.     

An NMR investigation of compatibility in blends of poly vinyl chloride and ethylene-vinyl acetate copolymer

A series of technical composite suspension polymerized poly vinyl chloride products with additions of ethylene-vinyl acetate copolymer (Levapren 450M. 45 wt % VAc) have been investigated with NMR. Partial compatibility is found in these samples, and the phase conditions have been shown to be very much dependent upon the methods of forming of the materials. Complete phase separation is observed after prolonged heating.     

Retardation of discoloration of poly(vinyl chloride) and decolorization of discolored poly(vinyl chloride) with diimide

Retardation of discoloration of poly(vinyl chloride) with diimide was studied in dimethylformamide at 130°C. with the use of p-toluenesulfonylhydrazide (PSH) as a source of diimide. A process was proposed that involved prolonging the induction periods of discoloration by inhibiting the development of conjugated polyene structure. The optimum proportion of PSH was one fourth of the poly(vinyl chloride), the best results. Furthermore, poly(vinyl chloride) discolored by thermal degradation in o-dichlorobenzene or gamma-ray irradiation under vacuum was decolorized in solution at 130°C. by addition of PSH. The decolorized poly(vinyl chloride) thus obtained was thermally stable compared with that obtained by oxidative methods.     

Structure Analysis of PVC Nanocomposites

In this paper poly(vinyl chloride)/clay nanocomposites were prepared by melt intercalation using a single screw extruder. Problems with thermal stability of these nanocomposites during compounding were largely eliminated by pre-treatment of the organoclay with plasticizer (dioctyl phthalate), which created a barrier between polymer and quaternary amine. These nanocomposite materials were analyzed with respect to their morphology. The intercalation, exfoliation, nano-phase dispersion and orientation were investigated using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and X-ray diffraction (XRD). Moreover, different types of sample preparation for these techniques were tested as well. It was found that partially intercalated and disordered structure arose in poly (vinyl chloride) composites containing sodium type of montmorillonite, while a fine dispersion of partial to nearly full exfoliation of individual montmorillonite layers in poly (vinyl chloride) matrix was observed when this clay was organically modified. Finally, the influence of different mixing time (in extruder) on nano-phase morphology was surveyed.     

Dehydrochlorination of poly(vinyl chloride) by aqueous sodium hydroxide solution under two-phase conditions

The reaction of poly(vinyl chloride) powder with aqueous sodium hydroxide solution in the presence of quaternary ammonium or phosphonium halides yielded dehydrochlorinated products of conjugated polyene structure. The reaction was discussed in terms of a phase transfer catalytic mechanism between aqueous and polymer phases. Among the catalysts used tetrabutylammonium bromide was the best. To obtain the optimum conditions the effects of reaction temperature, the concentration of NaOH and the catalyst, and the molecular weight of poly(vinyl chloride) were investigated. Treatment of PVC films and solutions in tetrahydrofuran with aqueous NaOH solutions under two-phase conditions also produced dehydrochlorinated films and powders.     

Fast synthesis of temperature-sensitive PNIPAAm hydrogels by microwave irradiation

A novel method, microwave irradiation synthesis, is proposed for the preparation of thermo-sensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels. The PNIPAAm hydrogels were separately synthesized by using microwave irradiation method and water-bath heating method. Chemical groups, lower critical solution temperature (LCST) and surface morphology of these PNIPAAm hydrogels were characterized by FT-IR, DSC and SEM. Swelling ratios of the gels were measured gravimetrically in the temperature range from 10.0 to 60.0 °C. Results showed that (1) the use of microwave irradiation can greatly shorten the reaction time required for PNIPAAm hydrogel synthesis from several hours to several minutes in comparison with water-bath heating method, and obviously improve the yields of the PNIPAAm gels, which were up to 99% after a short reaction time; (2) SEM micrographs and textural measurement revealed that the gels synthesized using microwave irradiation had more porous structure, and their average pore sizes and specific surface areas were larger than those of the gels synthesized using water-bath heating method; and (3) the PNIPAAm hydrogels synthesized using microwave irradiation had much higher swelling ratios at 10.0 °C below the LCST, and had lower swelling ratio at 60.0 °C above the LCST compared to the hydrogels synthesized by water-bath method.     

Microporous poly(vinyl methyl ether) hydrogels prepared by γ-ray irradiation at different heating rates

We prepared thermoresponsive and microporous polymer hydrogels by γ-ray irradiation of aqueous solutions poly(vinyl methyl ether) (PVME) at different heating rates. Under all temperature programs, opaque and heterogeneous PVME gels formed, which swelled at temperatures below the lower critical solution temperature and shrank at temperatures above it. All of the samples contained porous and phase-separated structures. The shape and size of the gel pores varied depending on the temperature programs. Gels having a sponge-like continuous porous structure formed only when the radiation-induced crosslinking was carried out at an optimum heating rate, which we found to be 0.11–0.13°C min⁻¹. For temperature changes between 10°C and 40°C, gels with this structure showed rapid volume transitions on a time scale of about a minute.     

THE COMPATIBILITY OF BLENDS OF POLY(VINYL CHLORIDE) OR CHLORINATED POLY(VINYL CHLORIDE) WITH POLY(METHYL METHACRYLATE)

IR spectral shifts of carbonyl vibrational absorption for ethyl acetate, which acts analogically as the structural unit of poly(methyl methacrylate), in cyclohexane, chloroform, chlorinated paraffins, poly(vinyl chloride) and chlorinated poly(vinyl chloride) were measured. The results suggest that there are specific interactions between the carbonyl groups and the chlorinated hydrocarbons which could be responsible for the apparent compatibility of poly(vinyl chloride)—poly(methyl methacrylate) and chlorinated poly(vinyl chloride)—poly(methyl methacrylate) blends. Additionally, the effects of the preparation mode of blend films on phase separation and observed compatibility are discussed.     

电子束辐照交联CB/HDPE凝胶复合物的阻温特性

对电子束辐照交联并经溶剂抽提得到的炭黑/高密度聚乙烯(CB/HDPE)凝胶复合物的阻温特性进行了研究.结果表明,凝胶复合物与未抽提的交联试样和未交联试样相比,其PTC强度显著增大,并伴有明显的NTC现象.经热冷循环后,表现出很好的阻温特性稳定性,并且NTC现象消失.表明阻温特性的稳定性及NTC现象的消除强烈依赖于CB/HDPE导电复合材料凝聚态结构的稳定性     

Thermal decomposition of poly(vinyl chloride) and chlorinated poly(vinyl chloride). II. Organic analysis

A concerted study of poly(vinyl chloride), chlorinated poly(vinyl chloride), and poly(vinylidene chloride) polymers by spectroscopy, thermal analysis, and pyrolysis-gas chromatography resulted in a proposed mechanism for their thermal degradation. Polymer structure with respect to total chlorine content and position was determined, and the influence of these polymer units on certain of the decomposition parameters is presented. Distinguishing differences were obtained for the kinetics of decomposition, reactive macroradical intermediates, and pyrolysis product distributions for these systems. It was determined that chlorinated poly(vinyl chloride) systems with long-chain ? CHCI? units were more thermally stable than the unchlorinated precursor, exhibited increasing activation energy for the dehydrochlorination, and produced chlorine-containing macroradical intermediates and chlorinated aromatic pyrolysis products. The poly(vinyl chloride) polymer was relatively less thermally stable, exhibited decreasing activation energy during dehydrochlorination, and produced polyenyl macro-radical intermediates and aromatic pyrolysis products.     

A comparative study of UV aging characteristics of poly(ethylene‐co‐vinyl acetate) and poly(ethylene‐co‐vinyl acetate)/carbon black mixture

In this comparative study, the effect of carbon black (CB) on the UV aging characteristics of poly(ethylene‐co‐vinyl acetate) (EVA) was investigated. EVA, containing 13% vinyl acetate (VA), and poly(ethylene‐co‐vinyl acetate)/carbon black mixture (EVA/CB), containing 13% VA and 1% CB, were aged by means of UV light with a wavelength in the vicinity of 259 nm, in air, up to 400 hr. Sol‐gel analyses were made to determine the percentage gelation of both virgin and aged samples. FT‐IR measurements were performed to follow the chemical changes which took place in the samples during aging. Dynamic and isothermal thermogravimetry studies were performed for determination of the thermal stabilities of virgin and aged samples. Sol‐gel analysis results showed that EVA itself has a tendency to form a gel under UV irradiation. EVA/CB, however, becomes a gel to a smaller extent, comparatively, under the same conditions. As a result of FT‐IR measurements, some oxidation products such as ketone, lactone and vinyl species were observed through UV ageing of EVA and EVA/CB. Thermal analysis experiments exhibited that the thermal stabilities of EVA and EVA/CB decreased, to a similar extent through UV aging. Copyright © 2004 John Wiley & Sons, Ltd.