Thermal Decomposition Behavior and Kinetics of Composites from Coal and Polyethylene

M2007rnal of China Uniof Mining technologyVol 17 No. 1Availableonlineatwww.sciencedirect.comSCIENCEdDIRECTSChina Univ mining Technol 2007, 17(1): 0025-0029Thermal Decomposition behaviorand Kinetics of Composites fromCoal and polyethyleneYANG Fu-sheng,, QU Jian-Iin, YANG Zhi-yuan, ZHOU An-ningSchool of Material Science and Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi710049, chinaDepartment of Chemistry and Chemical Engineering, Xi an University of Science Technology, Xi'an, Shaanxi 710054, ChinaAbstract: A thermogravimetric analysis (TG) was conducted to study the thermal decomposition behavior and kineticsof composites from coal and high density polyethylene(HDPE), linear low density polyethylene(LLDPE)or low denity polyethylene(LDPE). The results show that coal facilitates melting of the polyethylene before temperatures reach700 K in nitrogen due to the exothermic effect of coal. Above 700 K, adding coal into the polyethylene will result insmaller maximum rates of mass loss and higher initial mass loss temperatures of the composites. Hence, some chemicalinteractions, occurring between liquid compounds released in the pyrolysis of the coal and polymer, depend on severalfactors, such as coal rank and the molecular structure of polymers. Synergetic effects in coal and polymers were alsofound. Both chemical interactions and synergetic effects control the entire thermal decomposition behavior of compos-ites. The larger the amount of coal in the composites, the greater the decomposition temperature spans and the higherthe maximum decomposition temperature, the smaller the devolatilization rates. the effect of coal on the thermal stability of composites lies in the hydrogen acceptor effect of the coals. Thermal decomposition of the coals, the polymersand related composites can be modelled via first order parallel reactions between 563 K and 763 KKey words: coal; polyethylene; composite; thermal; kineticsCLC number: TQ 327.81 Introductionlization or degradation control of the composite, it isessential to discover the reactivity of the componentsIn the last few years, coal-based composites have and the thermal decomposition kinetics of compositeattracted much attention because of the excellent Thus, in our present study, thermal decompositionmacromolecular structural characteristics of coal. In behavior of the composites from two different typesexpanding fields of application, attempts have been of coal and industrial polyethylene were investigatedfunctional composites from coal and by means of TG measurementspolyolefins, such as conductive composites and controlled degradable film. Unfortunately, currently 2 Experimentalavailable literature on thermal decomposition ofcoal-based composites is rare. All the same, thermal 2.1 Materialsdecompositions of coal and polymers are intrinsicFor our analysis we have used Chinese Shenfuchemical reaction steps for the preparation of the (SF)and Huayingshan(HYS)coal. The results of thecomposite. Investigation into the kinetics of the ultimate and approximate analyses are summarized incomponents is important for process optimization. To Table 1. Coal samples were pulverized under 4 um inachieve good material properties, it is also necessary particle size. HDPE, LLDPE and LDPE used in theto conduct numerical simulation of the decomposition experiment are all commercial products and listed inprocess.Table 2 Composites from the coal and thIn order to improve our understanding of the stabwere preparedtwrin-ccrew extruder中国煤化工Received 03 June 2006; accepted 15 August 2006Project 06JK244 supported by the Special Foundation of Education Department of Shaanxi ProvinceCNMHGrespondingauthorTel:+86-29-85583183;E-mailaddressfushengyang(@163.comJournal of China University of Mining TechnolVol 17 No. 1model SJSH30, with a rotor speed of 120 r/min and blending ratios, was used as an example to showfeeding speed 20 r/min. SF/IF7B,different some primary properties of the composites(table 3)Table 1 properties of the coals used(%)Ultimate analysispproximate analysisNOVFC.dSE0.3881.754.7911.957.434.43364251.72HYS3.2887814.631.292.230.8616.8323.0959.22Table 2 Physical properties of the resins2 shows TG and DTG curves of polymers 6098, 7042and lF7B in nitrogenResinGrade nameDensity Melt flow rateHDPDGDA6098(6098)LLDPEDFDA7042(70420.5LDPEPE-FAS-18D075(IF7BTable 3 Properties of composite SF/IF7BBlend ratioMelt flow rate Tensile strength10:90▲-HYS26.12.5L- HYS400600800I00012004006008001000120060:400.6Temperature(K)Temperature(K)(a)TG(b)DTG2.2 Thermogravimetric analysis (TGA)Fig 1 TG and DTG curves of coals in nitrogenTG analyses were conducted on a NETZSCH TGA partial overlap in mass loss tempeerature ranges209C analyzer, using highly purified nitrogen as theof the coals and polymers can be easily observedpurge gas. Samples of approximately 15 mg were from Figs. I and 2. Moreover the same thermal de-heated to 1 173 K at a heating rate of 10 K/mincomposition mechanism, i. e, a radical chain scission2.3 Thermal decomposition kineticsmechanism, is proffered to explain the thermal decomposition behavior of polymers and coal 34)Coats and Redfern developed an integral method, Therefore, there might be interactions during thermalEq.(1), which can be applied to TG data. The correctreaction order n is presumed to lead to the best lineardecomposition of the composites to some extentpleg[g(a)]=1g 1E(1)E2.303RTAssuming that 2RT/Ea<