Investigations on poly(vinyl chloride). I. Evolution of aromatics on pyrolysis of poly(vinyl chloride) and its mechanism

Poly(vinyl chloride) (PVC) alone or mixed with 10 wt-% and 50 wt-% TiO₂, SnO₂, ZnO, and Al₂O₃ were pyrolyzed by using a pyrolysis gas chromatograph. Benzene, toluene, ethylbenzene, o-xylene, styrene, naphthalene, and various chlorobenzenes were identified. No hydrocarbons could be detected in pyrolysis products of any samples at 200°C. More aromatic hydrocarbons than aliphatic hydrocarbons are released from the PVC–TiO₂ system and in preheated PVC. The contrary result is observed in the PVC–ZnO and PVC–SnO₂ systems. Aromatics having methyl endgroups are easily released from the PVC–ZnO and PVC–SnO₂ systems and at elevated pyrolysis temperature, because methylene groups are easily isolated along the chain by ZnO, SnO₂ and the heating. The release of ethylbenzene o-xylene, and chlorobenzenes suggests a repeated dehydrochlorination and recombination of HCl and Cl₂ to double bonds along the chain. Possible decomposition mechanisms of PVC are discussed.     

基于热重红外联用分析的PE、PS、PVC热解机理研究

利用TGA-FTIR联用技术考察了PE、PS、PVC三种典型塑料的热解特性。结果表明,热稳定性从弱到强依次为PVC、PS、PE。PE热解反应过程为典型的一段式反应,红外光谱分析结果表明,PE热解过程为无规则断链形式,生成产物成分复杂,且随热解过程而改变,开始以饱和烃基团为主,中后期以烯烃基团为主,同时有少量炔烃;PS热解过程同样为一段式反应,红外光谱显示主要热解产物为苯乙烯单体,说明热解过程主要是苯乙烯的解聚过程;PVC热解过程较为复杂,主要分为脱氯阶段和共轭多烯重构阶段,红外光谱结果表明,产物中有芳香族化合物。脱氯过程和共轭多烯重构、环化过程在时间和空间上有重合,给二噁英类污染物的生成制造了可能。     

Gelation/fusion behavior of PVC plastisol with a cyclodextrin derivative and an anti-migration plasticizer in flexible PVC

We successfully evaluated the effects of 2,3,6-per-O-benzoyl-β-cyclodextrin (Bz-β-CD) on the rheological properties of PVC plastisols and the migration behavior of plasticizer from flexible PVC. Two types of plasticizer, di-isononyl phthalate (DINP) and diisononyl cyclohex-4-ene-1,2-dicarboxylate (Neocizer), along with Bz-β-CD as a migration inhibitor were mechanically mixed into an emulsion grade PVC resin to prepare plastisols. The presence of Bz-β-CD was expected to facilitate formation of stable complexes with DINP or Neocizer in the flexible PVC. It was necessary to determine whether changes in the processing conditions of the PVC plastisol were needed for use in this application. To this end, the viscoelastic properties of the plastisols, including the elastic modulus, G′, and the viscous modulus, G″, were continuously monitored as a function of temperature during the gelation and fusion processes using rheological analysis techniques. The results showed that complete gelation was slightly delayed and both moduli (G′ and G″) decreased upon addition of Bz-β-CD to the PVC matrix. FE-SEM images yielded insight into the gelation and fusion processes. The curing conditions and physical properties of the flexible PVCs containing Bz-β-CD were optimized, and the influence of Bz-β-CD on the migration of the plasticizers and the stability of the flexible PVC was studied. The results showed that Bz-β-CD reduced migration of DINP and Neocizer from the flexible PVC by almost 40% and 25%, respectively, thereby favorably restricting migration within the flexible PVC.     

Pyrolysis–gas chromatographic analysis of poly(vinyl chloride). II. In situ absorption of HCl during pyrolysis and combustion of PVC

A pyrolysis–gas chromatographic technique for measuring the amount of hydrogen chloride released during the high temperature pyrolysis of poly(vinyl chloride) resins, plastisols, copolymers and compounds containing inert fillers has been developed. The technique, which is also applicable to the analysis of chlorinated polyethylene and chlorinated poly(vinyl chloride), is based on the use of a standard precursor of HCl, poly(vinyl chloride) homopolymer. The analysis has been successfully used to measure the degree of in situ absorption of HCl during pyrolysis by certain basic fillers [K₂CO₃, CaCO₃, CaO, MgO, Al(OH)₃, Na₂CO₃, Al₂O₃ and LiOH] dispersed in a poly(vinyl chloride)–o-dioctyl phthalate matrix. Combustion of a number of combustion residues (chloride determination) revealed that the amount of HCl absorbed by the basic filler was independent of the method of degradation (pyrolysis or combustion). Flammability measurements of those matrices having the same composition indicate that in situ absorption of HCl during combustion has little effect on the overall flammability of these materials.     

Thermal and burning properties of wood flour-poly(vinyl chloride) composite

The present study deals with the effects of wood flour on thermal and burning properties of wood flour-poly(vinyl chloride) composites (WF-PVC) using thermogravimetric (TG), cone calorimetry (CONE), and pyrolysis?Cgas chromatography/mass spectrometry (Py?CGC/MS). TG tests show that an interaction occurred between wood flour and PVC during the thermal degradation of WF-PVC. Wood flour decreased the temperature of onset of decomposition of PVC. However, the char formation could be increased by adding wood flour to PVC. CONE test indicates that wood flour had positive effects on heat release and smoke emission of PVC. Comparing with PVC, WF-PVC reduced average heat release rate and the peak HRR by about 14 and 28%, respectively; smoke production rate was also decreased. The degradation mechanism was studied by Py?CGC/MS. The results show that the volatile pyrolysis products of WF-PVC are very different from PVC. The yields of HCl and aromatic compounds decreased dramatically, and the aliphatic compounds increased by the incorporation of WF.     

Rapid identification of additives in poly(vinyl chloride) lid gaskets by direct analysis in real time ionisation and single‐quadrupole mass spectrometry

Gaskets for lids of glass jars usually consist of poly(vinyl chloride) (PVC) containing plasticisers and additional additives, which may migrate into packed foodstuffs. To conform to legal regulations, any such migration has to be determined analytically, which is a big challenge due to the huge chemical variety of additives in use. Therefore, a rapid screening method by means of direct analysis in real time mass spectrometry (DART‐MS), using a single‐quadrupole mass spectrometer, was developed. On introducing a plastisol sample into the DART interface, protonated molecules and ammonium adducts were obtained as the typical ionisation products of any additives present, and cleavages of ester bonds as typical fragmentation processes. Generally, additives present in the 1% range could be directly and easily identified if ion suppressive effects deriving from specific molecules did not occur. These effects could be avoided by analysing toluene extracts of plastisol samples, and this also improved the sensivity. Using this method, it was possible to identify phthalates, fatty acid amides, tributyl O‐acetylcitrate, dibutyl sebacate, bis(2‐ethylhexyl) adipate, 1,2‐diisononyl 1,2‐cyclohexanedicarboxylate, and even more complex additives like acetylated mono‐ and diacylglycerides, epoxidised soybean oil, and polyadipates, with a limit of detection of ≤1% in PVC plastisols. Only in the case of epoxidised linseed oil were levels of ≥5% required for identification. The detection of azodicarbonamide, used as a foaming agent within the manufacturing process, was possible in principle, but was not highly reproducible due to the very low concentrations in plastisols. Copyright © 2009 John Wiley & Sons, Ltd.     

Studies of the effects of copper, copper(II) oxide and copper(II) chloride on the thermal degradation of poly(vinyl chloride)

Investigations of the pyrolysis of poly(vinyl chloride) (PVC) in the presence of copper metal (Cu), copper(II) oxide (CuO) and copper(II) chloride (CuCl₂) are of potential importance because of the likelihood of the formation of these copper compounds during the thermal degradation of PVC-coated copper wires, a step in the recovery of copper from waste. The presence of Cu, CuO and CuCl₂ (i) retards the thermal degradation of PVC in air and in nitrogen and (ii) decreases the percentages of volatile products produced at both stages of the decomposition. These effects are greatest for PVC-CuO. The presence of copper, CuO or CuCl₂ in PVC has a major effect on the nature of the gaseous emissions of the thermal decomposition in air and in nitrogen. The concentrations of total chlorine, aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons and soot particulates are all affected relative to an equivalent amount of PVC. These changes are greatest for the PVC-CuO system for which total chlorine emissions in air and nitrogen are reduced by 40% in air and 20% in nitrogen, benzene emissions are reduced by greater than 90% in air and nitrogen, other aromatic and chloroaromatic emissions are reduced, and soot particulate emissions are reduced by more than 50% as the concentrations of aliphatic compounds are increased. These changes are consistent with the presence of copper or its compounds permitting more efficient combustion of the carbon content of the PVC and particularly in the case of PVC-CuO with the removal of chlorine during pyrolysis in the inorganic phase.     

Preparation and performance of plasticizers for poly(vinyl chloride) from products of thermal decomposition of waste polystyrene

2,4-Diphenylbutyl-2,4-diphenylbutyrate (DPBDPB) and 2,4,6-triphenylhexyl-2,4,6-triphenylhexoate (TPHTPH), plasticizers for poly(vinyl chloride), were synthesized from the products of thermal decomposition of waste polystyrene. Their heat stabilities were studied by thermogravimetric analysis and differential thermal analysis, and compared with those of typical plasticizers for PVC such as dibutyl phthalate (DBP), dihexyl phthalate (DHP) and bis(2-ethylhexyl) phthalate (DOP). DPBDPB and TPHTPH showed much higher heat resistance than DOP. PVC was plasticized with a mixed system consisting of DOP as the primary plasticizer and DPBDPB as the secondary. It became clear that DPBDPB is an excellent heat-resistant plasticizer which does not affect the compatibility of PVC with DOP.     

油页岩的~(13)C-NMR特征及FLASHCHAIN热解模拟研究

采用固体13C-NMR核磁共振技术表征了甘肃窑街矿区油页岩的碳骨架结构,分析并计算了油母质团簇化学结构参数,包括团簇平均碳原子数、芳碳原子数、脂碳原子数及芳环数。在热重红外分析仪(TG-FTIR)上进行了油页岩的热解实验,得到了热解产物的生成规律。结合样品的团簇化学结构参数,采用基于油页岩结构的FLASHCHAIN模型模拟其热解产物的生成过程;模拟结果与TG-FITR实验数据符合较好,印证了模型预测的合理性。     

旋转模塑过程中PVC溶胶物理凝胶化转变的有限元分析

采用有限元法,数值模拟了成型过程中镍制模具和PVC材料的非稳态温度场,进而得到了PVC材料结构参数的时间演变和空间分布规律,再由结构-性能关系获得了PVC材料的溶胶黏度及其演变特点,在此基础上比较分析了不同增塑剂对PVC材料物理凝胶化转变过程的影响.结果表明,由于热阻不同,靠近模具壁的PVC溶胶升温速率较大,首先发生凝胶化转变;加热过程中,PVC材料的黏度首先降低至最小值,凝胶化转变开始后,PVC树脂和增塑剂之间的相互作用增强,材料黏度迅速升高;不同增塑剂对材料结构参数和溶胶黏度的演变规律有着不同影响.     

Quantitative comparison of the nitrogen-containing pyrolysis products and amino acid composition of soil humic acids

Pyrrole and acetonitrile, major pyrolysis products of soil humic substances, vary characteristically in abundance with the degree of humification of the organic matter in the soil. Their origin, however, is uncertain because of the large amount of unidentifiable soil nitrogen. A quantitative relationship between amino acid composition and pyrrole and acetonitrile abundances has been established by Curie-point pyrolysis-gas chromatography of a group of test proteins, using polystyrene as an internal standard. The pyrolysis yields of these products from three humic acids extracted from the surface horizons of Scottish brown forest soils (Cambisols or Ochrepts) were entirely accounted for by the known hydrolysable amino acid content and composition, and the products were related to individual amino acids. The peptide amino acid was also found to be the overall source of the aromatic pyrolysis products toluene, phenol and p-cresol.     

Investigations on poly(vinyl chloride). II. Pyrolysis of chlorinated polybutadienes as model compounds for poly(vinyl chloride)

The pyrolysis of chlorinated polybutadienes (CPB) was investigated by using a pyrolysis gas chromatograph. CPB corresponds to poly(vinyl chloride) (PVC) constructed with head–head and tail–tail linkages of the vinyl chloride unit. Benzene, toluene, ethyl-benzene, o-xylene, styrene, vinyltoluene, chlorobenzenes, naphthalene, and methylnaphthalenes were detected in the pyrolysis products from CPB above 300°C, and no hydrocarbons could be detected at 200°C. The pyrolysis products from CPB were similar to those from PVC and new products could not be detected. Lower aliphatics, toluene, ethylbenzene, o-xylene, chlorobenzenes, and methylnaphthalenes were released more easily from pyrolysis of CPB than from PVC; amounts of benzene, styrene, and naphthalene formed were small. These results support the conclusion that recombination of chlorine atoms with the double bonds in the polyene chain takes place and that scission of the main chain may depend on the location of methylene groups isolated along the polyene chain during the thermal decomposition of PVC.     

Thermal decomposition of polybutadienes by pyrolysis gas chromatography

The thermal decomposition of cis-1,4-, trans-1,4-, and 1,2-polybutadienes (PBD) in the temperature range 450–900°C was investigated by pyrolysis gas chromatography (PGC). The cis- and trans-PBDs have closely similar product distribution and can be readily distinguished at lower temperatures of pyrolysis from the 1,2-PBD by the low amount of vinyl cyclohexene (VCH) produced by the 1,2 species. The amount of butadiene (BD) produced by 1,2-PBD varies with the tacticity of the polymer; the greater syndiotactic yields a lesser amount of BD. A method of determining the 1,4 and the 1,2 contents of PBD based on the ratios of peak heights of ethylene (C2) to VCH, propylene (C3) to VCH, and BD to VCH is presented. The advantages of this method are discussed. The nature and composition of the products of pyrolysis in the temperature range 540–900°C are presented and the mechanism of degradation at these elevated temperatures is explained.     

Analysis of products from the pyrolysis of plastics recovered from the commercial scale recycling of waste electrical and electronic equipment

Three plastic fractions from a commercial waste electrical and electronic equipment (WEEE) processing plant were collected and investigated for the possibility of recycling them by batch pyrolysis. The first plastic was from equipment containing cathode ray tubes (CRTs), the second plastic was from refrigeration equipment, and the third plastic was from mixed WEEE. Initially, the decomposition of each of the plastics was investigated using a TGA linked to a FT-ir spectrometer which showed that the CRT plastic decomposed to form aliphatic and aromatic compounds, the refrigerator plastic decomposed to form aldehydes, CO₂, aromatic, and aliphatic compounds, and the mixed WEEE plastic decomposed to form aromatic and aliphatic compounds, CO₂, and CO. Each plastic mixture was also pyrolysed in a batch reactor to determine the halogen and metal content of the pyrolysis products, additionally, characterisation of the pyrolysis oils was carried out by GC–MS and the pyrolysis gases by GC–FID and GC–TCD. It was found that the halogen content of the oils was relatively low but the halogen and metal content of the chars was high. The pyrolysis oils were found to contain valuable chemical products and the pyrolysis gases were mainly halogen free, making them suitable as a fuel.     

Effect of branching on the degradation behaviour and caloric properties of PVC

Nine different PVC samples with defined chlorine content and degree of branching have been investigated. The aim of the work was the influence of these parameters on some caloric properties as well as the degradation behaviour and the degradation products. As expected, the heat of combustion decreases with increasing chlorine content. As determined by simultaneous thermal analysis/mass spectrometry, the volatile degradation products of the pyrolysis in nitrogen atmosphere vary. The higher the chlorine content, the higher the amount of chlorinated degradation products and the lower the amount of polycyclic aromatic hydrocarbons (PAH). A higher number of branching promotes the formation of alcylated aromatic hydrocarbons.     

Network formation by epoxidised soybean oil in plastisol poly(vinyl chloride)

Epoxidised soybean oil, ESBO, is a well known additive used in plasticized poly(vinyl chloride) (PVC) since it functions both as plasticizer and as stabilizer. This paper describes what happens to the material when ESBO is used as primary plasticizer in plastisol- and in suspension PVC without any additional stabilizer. When 50 ph ESBO was added to 100 ph plastisol PVC and then aged in a Werner Mathis oven at 180 °C for various lengths of time, the E-modulus increased with ageing time due the formation of a crosslinked network induced by a polymerization reaction of the epoxy groups in the ESBO. The network and the PVC were analyzed by NMR which showed that reaction between PVC and ESBO had occurred, and that the network consisted primarily of ESBO. The same experiment performed with suspension PVC instead of plastisol PVC did not result in any crosslinking of the ESBO. The ring opening of the epoxy which starts the polymerization of ESBO is most likely catalyzed by an additive used in the polymerization of plastisol PVC.     

Synthesis and properties of phosphorus-containing polyesters derived from 2-(6-oxido-6H-dibenz〈c,e〉〈1,2〉oxaphosphorin-6-yl)-1,4- hydroxyethoxy phenylene

A series of phosphorous-containing aliphatic polyesters were synthesized by high-temperature solution condensation of 2-(6-oxido-6H-dibenz〈c,e〉〈1,2〉oxaphosphorin-6-yl)-1,4-hydroxyethoxy phenylene (III) with various aromatic acid chlorides in o-dichlorobenzene. All polyesters are amorphous and readily soluble in many organic solvents such as DMAc, NMP, DMSO, and o-dichlorobenzene at room temperature or upon heating. These polyesters are thermally quite stable. The glass transition temperatures of these aliphatic polyesters ranged from 126.6 to 162.2°C. The degradation temperatures (T_d onset) in nitrogen ranged from 424 to 448°C, and the char yields at 700°C are 20–32%. The activation energies of degradation ranged from 160.9 to 226.0 kJ/mol. The LOIs of these polyesters ranged from 36 to 43. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3051–3061, 1998     

Pyrolysis behavior of phosphorus polyesters

The pyrolysis behavior of aromatic–aliphatic polyesters containing either a pendant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) group or a phosphine oxide group incorporated into the polymer backbone was studied using a combination of thermogravimetry and pyrolysis-GC/MS. The behavior of the phosphorus polyesters was compared to that of non-phosphorus-containing reference polymers. It could be shown that the DOPO group mainly does not interfere with the polyester decomposition. It produces two main pyrolysis products, o-hydroxybiphenyl and dibenzofuran, with the latter one requiring a higher pyrolysis temperature. Minor products containing the DOPO ring result from secondary decomposition reactions. In contrast, the phosphine oxide group strongly modifies the polyester pyrolysis behavior by decreasing the degradation temperature and changing the composition of pyrolysis products. Among of those, phosphinites and a phosphinate could be identified indicating rearrangement processes of the phosphine oxide group taking place upon pyrolysis. Mass spectra of organophosphorus products and pyrolysis schemes of polyesters are discussed.     

Chlorinated products of plastic pyrolysis

The formation of various chlorinated products in pyrolysis of polymers and plastics additives was studied. Formation of chlorobenzenes (in addition to the monomers) from poly(chlorostyrene) and poly(vinylbenzyl chloride) was observed. Hydrogen chloride is only produced from these polymers at above 600 °C when the chlorine atoms are cleaved off and abstract hydrogen. A similar process takes place in aromatic chlorine-containing dyes, in which the strong aromatic molecular structure prevents the thermal cleavage of chloroaromatic volatile products. We have observed that cupric and ferric chlorides chlorinate phenolic thermal decomposition products of plastic materials which originate either from the polymer or from the stabilizer. The highest yields of chlorophenols are obtained in pyrolysis at around 700 °C.     

废弃印刷电路板材料裂解产物的高分辨裂解气相色谱-质谱分析

采用高分辨裂解气相色谱-质谱法(PyGC-MS)分析了FR-4型印刷电路板粉末样品的裂解产物。在氦气氛围中,分别在350,450,550,650和750 ℃下对印刷电路板粉末样品进行热裂解,并通过毛细管气相色谱-质谱对裂解产物进行分析,研究了不同裂解温度下裂解产物分布以及主要裂解产物的产率与裂解温度的关系,根据热分解产物的组成,探讨了热分解反应机理。