Transformations of chlorinated organic additives in polystyrene in the course of oxidative pyrolysis

Oxidative pyrolysis of polystyrene containing chlorinated organic additives was studied by synchronous thermal analysis combined with mass spectrometry of decomposition products. Commercial polystyrene foam sample with unknown composition of fireproofing additives and artificially prepared polystyrene with an admixture of chlorinated paraffins were chosen as investigation objects. Under the conditions of oxidative pyrolysis, both samples decompose to form chlorinated organic compounds, including highly toxic phosgene.     

Chemical degradation of polystyrene induced by chlorinated nitrosobenzene

Chemically induced degradation of polystyrene (PSt) in the presence of 2,4,6-tri-chloronitrosobenzene (TCNB) as radical generator was investigated in benzene solution by means of the electron spin resonance (ESR) method. The ESR spectra observed after the addition of TCNB to PSt in benzene solution were assigned to the nitroxide radicals (spin adducts) of the PSt radicals,

,

and

. These assignments were deduced from comparisons between observed and computer simulated spectra and were supported by experiments using α-deuterated PSt. It was found by analyses of ESR spectra that two kinds of type (B) radicals were produced, which were different in local conformation. The radicals (A) and (B) were thought to be produced by hydrogen abstraction by the chlorinated phenyl radical which results from homolytic scission of the CN bond of TCNB on slight warming. On the other hand, it was concluded that β-scission of radical (A) results in the formation of the chain scission radical (C). The mechanism of degradation of PSt induced by TCNB as radical initiator is discussed, together with the decrease in molecular weight observed after the addition of TCNB to a PSt-benzene solution. From the decrease of molecular weight it is concluded that TCNB acts as a scission inducer.     

Hydrogen formation during pyrolysis of polystyrene

Hydrogen was identified as a product of the pyrolysis of polygyrene, especially at high pyrolysis temperatures. With a high interface temperature of the Pyroprobe foil pyrolyser and a high pyrolysis temperature, almost 100% of the pyrolysed polymer could be accounted for. It is then assumed that hydrogen (up to 26%) produces a corresponding amount of carbon, which remains on the foil.     

聚苯乙烯的催化裂解研究

由于塑料性质稳定,难以自然降解,其废弃物不仅严重污染环境,更造成了资源浪费.因此,废旧塑料的再资源化对环境保护和可持续发展有着重要意义.废塑料再资源化回收技术是指将废塑料热裂解或催化裂解、回收燃料油和化工原料的技术~([1,2]).     

Solubility of polystyrene in selectively deuterated methyl acetate

Cloud point measurements were made for binary systems of polystyrene (PS) + methyl acetate (MA) and polystyrene (PS) + selectively deuterated MA: CD₃COOCH₃ and CH₃COOCD₃ with three PS samples of M_w = 4.0 × 10⁵, 2.0 × 10⁶, and 13.2 × 10⁶. All systems are characterized by the phase diagrams with upper and lower critical temperature. H/D isotope effects on miscibility for both selectively deuterated acetates are very large and appeared to be independent of the site of deuterium substitution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47:2140–2143, 2009     

Synthesis of chlorinated 1,3-dioxanes

A new synthesis of chlorine-substituted 1,3-dioxanes is effected from methylallyl chloride and isocrotyl chloride by condensing them with paraformaldehyde in the presence of KU-2 cation-exchange resin.     

The thermodynamics of benzene adsorption on carbon obtained by the pyrolysis of hypercrosslinked polystyrene

The Glukauf chromatography method was used to study the adsorption of benzene on a microporous carbon material prepared by the pyrolysis of hypercrosslinked polystyrene. The thermodynamic characteristics of adsorption were determined as functions of the degree of pore filling. Over the range of relative pressures studied (<0.005), adsorption was shown to occur in ultramicropores by the mechanism of primary filling without condensed phase formation. Original Russian Text ? L.D. Asnin, V.A. Davankov, A.V. Pastukhov, K. Kaczmarski, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 7, pp. 1356–1359.     

The adsorption of chlorobenzene on a carbon adsorbent obtained by the pyrolysis of hypercrosslinked polystyrene

The adsorption of chlorobenzene vapor on an experimental D4609 (Purolite Int.) adsorbent prepared by the pyrolysis of hypercrosslinked polystyrene was studied. The adsorbent was characterized by a large specific surface area, a narrow pore size distribution with the predominant fraction of pore diameters 0.9–3.4 nm, and a high absorption ability with respect to chlorobenzene. The adsorption isotherms were measured over the temperature range 100–140°C, and the thermodynamic characteristics of adsorption were determined. In spite of the correspondence to the formal requirements of the theory of volume filling of micropores, the mechanism of adsorption in narrow micropores (<1.2—1.5 nm) was different from filling with a condensed phase.     

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。     

Flash pyrolysis of polystyrene wastes in a free-fall reactor under vacuum

Plastic waste minimization and recycling are important for both economical and environmental reasons. In this flash pyrolysis study, polystyrene wastes were degraded in a free-fall reactor under vacuum to regain the monomer. A set of experiments varied the temperature between 700 and 875°C and determined its effects on the phase yields, the benzene, styrene, toluene, and naphthalene distribution of the liquid output and C1–C4 content of the gaseous output. The liquid yield maximized around 750°C and the styrene yield at 825°C. In general, operating at higher temperatures lessened the solid residue and increased the gaseous yield and total conversion. Employing waste particles in four size ranges, a second set of runs indicated that the finer the waste particles fed the higher the gaseous yield and total conversion. This recycling method can be made more promising if the feed particles are allowed more time for degradation and the removal of the primary products speeded up thereby preventing their decomposition. Ways are suggested to obviate these residence time problems.     

含氟酰基胂叶德的合成及其裂解反应

作者曾报道三氟乙酰基亚甲基三苯基胂 和双(三氟乙酰基)亚甲基三苯基胂的合成, 发现这二种含氟胂叶立德非常 稳定, 难于和醛酮反应。通过对三氟乙酰基亚甲基三苯基胂晶体结构的测定。证实了其稳定性。本文将上述方法扩展, 用来合成多氟酰基胂叶立德和双(多氟酰基)胂叶立德。     

Synthesis of quantum dot-tagged submicrometer polystyrene particles by miniemulsion polymerization

Submicrometer fluorescent polystyrene (PS) particles have been synthesized via miniemulsion polymerization using CdSe/ZnS core-shell quantum dots (QDs). The influence of QD concentration, QD coating (either trioctylphosphine oxide (TOPO)-coated or vinyl-functionalized), and surfactant concentration on the polymerization kinetics and the photoluminescence properties of the prepared particles has been analyzed. Polymerization kinetics were not altered by the presence of QDs, whatever their surface coating. Latexes exhibited particle sizes ranging from 100 to 350 nm, depending on surfactant concentration, and a narrow particle size distribution was obtained in all cases. The fluorescence signal of the particles increased with the number of incorporated TOPO-coated QDs. The slight red shift of the emission maximum was correlated with phase separation between PS and QDs, which occurred during the polymerization, locating the QDs in the vicinity of the particle/water interface. QD-tagged particles displayed higher fluorescence intensity with TOPO-coated QDs compared to those with the vinyl moiety. The obtained fluorescent particles open up new opportunities for a variety of applications in biotechnology.     

Further considerations of the sources of the volatiles from pyrolysis of polystyrene

Formation of the radical precursor to trimer (T) during pyrolysis of polystyrene features a 1,5-hydrogen shift. However because 1,3-shift is so much slower, the sources of the less abundant dimer (D) and tetramer (Te) remain unclear. While we and others have proposed addition of small radicals to olefinic polymer end-groups as a route to oligomer precursor radicals, others recently suggested that such addition is also too slow and proposed a third alternative: 1,7-shift followed serially by 7,3-shift to give the precursor for D. Although considerable evidence suggests that 1,7-shift would be much slower than 1,5-shift, this alternate kinetic model assigned them as comparably rapid. We apply a computational method to predict initial product distributions based on estimated, and empirically varied, propagation rate constants for 1,x-shift, β-scission, hydrogen transfer, and addition radical steps. The addition mechanism successfully predicted the relative amount of D but systematically underestimated Te. This deficiency could be removed by empirical inclusion of a small amount of 1,7-shift, although the other literature evidence still causes this to remain a questionable hypothesis.     

Adsorption of hexane, cyclohexane, and benzene on microporous carbon obtained by pyrolysis of hypercrosslinked polystyrene

The relationships of adsorption of hexane, cyclohexane, and benzene on a D4609 microporous carbon adsorbent obtained by the pyrolysis of hypercrosslinked polystyrene are compared. It is shown that in the range of relative pressures corresponding to the filling of ultramicropores, the adsorption behaviors of cyclohexane and benzene are essentially identical, in contrast to hexane, which is characterized by higher adsorption values and isosteric heat of adsorption. The observed relationships are explained by the steric features of the distribution of molecules of various structures in ultramicropores.     

Synthesis of branched polystyrene by ATRP exploiting divinylbenzene as branching comonomer

Branched polystyrenes have been synthesized using atom transfer radical polymerization (ATRP) of styrene in the presence of divinyllbenzene (DVB) as branching comonomer. The synthesis was completed via facile one pot approach. Mole ratio of styrene to DVB in range of 5:1-30:1 was employed to obtain soluble polymers. The kinetics of the polymerization and evolution of polymer compositions were revealed by determining the conversions of reactants by gas chromatography (GC). The growth of molecular weight was monitored by GPC and the results indicate that the branched polymers were formed by self-condensing vinyl polymerization (SCVP) of AB^∗ monomer or macromonomers. The branched structure of the resulting polymers was confirmed by the remarkable discrepancies of the weight average molecular weights determined by GPC and multi angle laser light scattering (MALLS). The specific viscosity of the resulting polymer is also much lower compared with that of linear analogues. The influence of dosage of initiator and catalyst on the yield and molecular weights of the resulting polymers was also investigated.