摘要
聚氯乙烯(Poly(vinyl chloride), PVC)在建材领域有着广泛的应用,产品形式包括型材、管材、板材等。当制品达到使用年限或遇到建筑物拆迁,就不可避免地带来大量废弃物,对生态环境构成威胁。再生利用是解决问题的最佳办法,但目前大多是降级回收,即再生制品性能比原始制品下降很多。如果在再生之前对回收料的再生价值进行评估,则有利于合理高效地加以利用,对保护环境、节约资源、促进可持续发展具有重大意义。
本论文首先在综述国内外研究成果的基础上提出:决定PVC回收料再生性能的因素主要为化学成分(树脂、填料等含量)、残余热稳定性以及PVC树脂的老化程度,为了科学、高效地利用PVC回收料,必须对上述因素进行测试,进而评估其再生价值。第二,对回收料中的PVC树脂、交联PVC、热稳定剂、填料进行分离和分析,表明,不同来源的回收料化学组成差异很大,与原产品的配方、加工工艺、使用环境和时间有关。第三,采用热重法(TG)测定和比较PVC原始料VS和回收料R1的热稳定性,运用Flynn-Wall-Ozawa方法计算两者在N2下降解反应的表观活化能,即转化率为10%和20%时,前者分别为143 kJ/mol和145 kJ/mol,后者都是132 kJ/mol;Kissinger方法计算的结果分别为138 kJ/mol和124 kJ/mol;采用Toop方程预测了样品在不同温度下的使用寿命,原始料为回收料的2-9倍,表明样品VS的热稳定性比R1的差。第四,为了了解老化程度与树脂结构之间的关系,对PVC(与热稳定剂复配)进行热氧老化试验,综合运用傅立叶变换红外光谱(FTIR)、凝胶渗透色谱(GPC)和紫外-可见光谱(UV-Vis)对样品的分子结构进行表征。结果表明,老化后,PVC分子链上发生氧化反应生成羰基;树脂的数均分子量随老化时间递增;分子链上脱去HCl生成共轭多烯链,并且其长度和浓度随老化时间的延长和温度的升高都在不断增加;定义450nm处的吸光度为PVC老化程度的度量,利用阿伦尼乌斯方程计算了PVC样品在试验条件下老化反应的表观活化能,Ea=113 kJ/mol。第五,对回收样品R1、R2、R3和经过一次热加工的样品N(未使用过)中的树脂以及原始树脂V的分子结构进行表征和比较。结果表明,回收样品和经过热加工的样品的数均分子量都较原始树脂有不同程度地增加,分子量分布也变宽;分子链上羰基指数反映了样品被氧化的程度,其顺序为R3>R2>R1>N>V;树脂分子上含有不同长度和浓度的共轭多烯链; 450nm处的吸光度反映样品的老化程度,其顺序为R1>R2>R3>N>V;估算了回收样品R1、R2和R3在30℃下已使用的时间(理论计算值),分别为45年、15年和7年。最后,对全文的工作和成果进行了总结,并提出了对PVC回收料的再生价值进行检测和评价的方法。
本论文的研究成果可以为评价PVC回收料的再生价值提供检测方法;为鉴定PVC制品是原始料制品还是回收料制品提供测试方法;为PVC废弃物的再生利用提供技术支持,促进该行业的健康发展;有利于降低和消除PVC废弃物带来的环境污染,促进资源的综合利用;为其它种类塑料废弃物再生利用提供参考和借鉴。
Poly(vinyl chloride) (PVC) has found broad application in building materials, in the forms of profile, pipe, board, etc. While the buildings are dismantled or reaching the lifetime, PVC products bring about a great deal of wastes inevitably, which poses a threat to the ecological environment. The best solution is reclaiming and reusing, however most of the time the wastes are reclaimed in a degrading way, which means the properties of the recycled products are much inferior to that of the original ones. So evaluating the recycling properties of the recyclate before reuse helps to make full use of these wastes in a reasonable and efficient way, and then to protect environment, economize resource and promote sustainable development.
In the present paper, the research progress and achievements in this field around the world were reviewed firstly. Based on this, the idea was proposed, that the properties of the recyclate are mainly determined by its chemical composition, residual thermal stability and the ageing degree of the PVC resin within it. To make use of PVC recyclate scientifically and efficiently, the determining factors above-mentioned must be tested, and then its recycling properties can be assessed. Secondly, PVC resin, crosslinked PVC, thermal stabilizer and filler in recyclate were seperated and analyzed. It indicated that the samples from different source varied in their compositon, which was related to their formula, processing, serving condition and time. Thirdly, the thermogravimetry was employed to test and compare the thermal stability of recycled and virgin PVC. When the conversion of the degrading reaction reached 10% and 20%, the activation energy of degradation in N2, calculated by Flynn-Wall-Ozawa method were 143 kJ/mol and 145 kJ/mol for the virgin one, and both 132 kJ/mol for the recycled one. The values calculated by Kissinger method were 138 kJ/mol and 124 kJ/mol, respectively. Toop equation was applied to predict the lifetime of the two samples when they served under different temperatures, and the value of the virgin sample is 2-9 times longer than that of the recycled one, which indicated that the thermal stability of the recycled sample was worse than that of the virgin one. Fourthly, to understand the relationship between the ageing degree and molecular structure of PVC resin, the PVC samples(formulated with thermal stabilizer) were thermooxidatively aged under 140℃、150℃and 160℃respectively. Then GPC, FTIR and UV-Vis spectrum were employed to characterize the samples aged. The results demonstrated that carbonyl group developed through oxidation reaction on the molecular chain, the number average molecular weight increased with ageing, and HCl shucked off, producing polyene, the length and concentration of the polyene ever-increased with the time of ageing increasing or the temperature rising. The absorbance at 450nm in UV-Vis spectrum was defined as the ageing degree of PVC, then the activation energy of ageing under the condition of the experiment was calculated through Arrhenius equation, that was 113 kJ/mol. Fifthly, the molecular structure of PVC resin within the recycled samples R1, R2, R3, sample N(thermally processed once, not used) and the virgin PVC resin were comprehensively characterized by GPC, FTIR and UV-Vis spectrum. It indicated that the number average molecular weight of R1, R2, R3 and N were higher than that of the virgin resin in varying degrees, and their molecular weight distributions were wider. The sequence of the carbonyl index indicating the oxidation degree, was R3>R2>R1>N>V; There were polyenes with different length and concentration. The sequence of the absorbance at 450nm in UV-Vis spectrum, which indicated the ageing degree, was R1>R2>R3>N>V. The duration that recycled samples R1, R2 and R3 had served at 30℃were roughly calculated, that were 45 years, 15 years and 7 years (theoretical values), respectively. Lastly, the work and achievement were concluded, and the method and approach of assessing recycled PVC were proposed.
The achievement of the present paper helps to develop testing menthods for evaluating recycling quality of the PVC recyclate, and the methods to identify the virgin products from recycled ones. It can provide technical support to the recycling of PVC wastes, advancing the healthy development of the recycling industry. It contributes to reducing or even eliminating the harm to environment caused by PVC wastes, and pushing forward the full use of resource. It also affords reference to the recycling of other kinds of plastic wastes.
引文
[1]谢建玲,桂祖桐,蔡绪福.聚氯乙烯树脂及其应用.北京:化学工业出版社, 2007
[2] GB 5761,悬浮法通用型聚氯乙烯树脂的物化性能
[3]张如意.聚氯乙烯塑料制品的老化机理与防老化机理.焦作工学院学报. 1996,(6):89-93
[4] Mikiya Ito,Kazukiyo Nagai. Analysis of degradation mechanism of plasticized PVC under artificial aging conditions. Polymer Degradation and Stability, 2007,92 : 260-270
[5] Luis Pimentel Real, Jean-Luc Gardette. Ageing and characterisation of PVC-based compounds utilised for exterior applications in the building construction field 1: Thermal ageing. Polymer Testing, 2001, 20: 779–787
[6] R. Benavides, B.M. Castillo, A.O. Castaneda. Different thermo-oxidative degradation routes in poly(vinyl chloride). Polymer Degradation and Stability, 2001,73 : 417–423
[7] K. Z. Gumargalieva, V. B. Ivanov, G. E. Zaikov. Problems of ageing and stabilization of poly(viny1 chloride). Polymer Degradation and Stability, 1996, 52: 73-79
[8] M. Ekelund, H. Edin,U.W. Gedde. Long-term performance of poly(vinyl chloride) cables. Part 1: Mechanical and electrical performances. Polymer Degradation and Stability, 2007, 92: 617-629
[9] Luis Pimentel Reala,Jean-Luc Gardetteb,Ade′lia Pereira Rocha. Artificial simulated and natural weathering of poly(vinyl chloride) for outdoor applications:the influence of water in the changes of properties. Polymer Degradation and Stability,2005,88 : 357-362
[10] Luis Pimentel Reala,Ade′lia Pereira Rochaa, Jean-Luc Gardette. Artificial accelerated weathering of poly(vinyl chloride) for outdoor applications:the evolution of the mechanical and molecular properties. Polymer Degradation andStability,2003,82: 235–243
[11] C. Anton-Prinet, J. Dubois, G. Mur. Photoageing of rigid PVC-II. Degradation thickness profiles. Polymer Degradation and Stability,1998,60: 275-281
[12] C. Anton-Prinet,G. Mur. Photoageing of rigid PVC-III. Influence of exposure conditions on the thickness distribution of photoproducts. Polymer Degradation and Stability, 1998, 60: 283-289
[13] C. Anton-Prinet, G. Mur. Photoageing of rigid PVC-IV. Effects of titanium dioxide. Polymer Degradation and Stability, 1998, 61: 211-216
[14] W. Manzoor, S. M. Yousaf, Z. Ahmad. Degradation of PVC: Effect of zinc chloride on the concentration of polyenes. Polymer Degradation and Stability, 1996, 51: 295-299
[15]徐国敏,秦舒浩,鲁圣军. PVC的环境问题.聚氯乙烯, 2007, (11): 1—4
[16] Nazdaneh Yarahmadi, Ignacy Jakubowicz, Thomas Gevert. Effects of repeated extrusion on the properties and durability of rigid PVC scrap. Polymer Degradation and Stability, 2001, 73: 93–99
[17] Herbst H, Ho.man K, Pfaendner R. Frontiers in the science and technology of polymer recycling. Dordrecht, The Netherlands: Kluwer Academic Publishers, 1998.
[18] MA WENCUANC, F. P. LA MANTIA. Processing and Mechanical Properties of Recycled PVC and of Homopolymer Blends with Virgin PVC. Journal of Applied Polymer Science, 1996, 59: 759-767
[19] Dietrich Braun. Recycling of PVC. Progress in Polymer Science. 2002, 27: 2171–2195
[20] GB/T 2917-2002,塑料—以氯乙烯均聚物和共聚物为主的共混物及制品在高温时放出氯化氢和任何其它酸性产物趋势的测定
[21] Nazdaneh Yarahmadi, Ignacy Jakubowicz, Lars Martinsson. PVC floorings as post-consumer products for mechanical recycling and energy recovery. Polymer Degradation and Stability, 2003, 79: 439–448
[22] Ignacy Jakubowicz, Nazdaneh Yarahmadi, Thomas Gevert. Effects of accelerated and natural ageing on plasticized polyvinyl chloride (PVC).Polymer Degradation and Stability, 1999, 66: 415-421
[23] Nazdaneh Yarahmadia, Ignacy Jakubowicza, Thomas Hjertbergb. The effects of heat treatment and ageing on the mechanical properties of rigid PVC. Polymer Degradation and Stability, 2003, 82: 59–72
[24] J.C. Arnold, B. Maund, D.H. Isaac. The mechanical properties of recycled PVC bottle compounds. Journal of Materials Processing Technology, 1996, 56: 475-481
[25] J. C. ARNOLD, B. MAUND. The Properties of Recycled PVC Bottle Compounds. 1 : Mechanical Performance. Polymer Engineering and Science. 1999, 39: 1234-1241
[26] J. C. ARNOLD, B. MAUND. The Properties of Recycled PVC Bottle Compounds. 2: Reprocessing Stability. Polymer Engineering and Science. 1999, 39: 1242-1250
[27]慕柳. PVC的再生利用已成现实.中国建筑防水, 2008, (6): 41-43
[28]陈分珍.废旧聚氯乙烯再生技术研究进展.国外塑料, 2006, 24, (11): 75-77
[29]李青山,公玲,梁春雨.废旧聚氯乙烯-粉煤灰复合材料的研究.粉煤灰综合利用, 2000, (4): 26-28
[30]樊芷芸,蒋莉,尹艺青.废旧塑料在建筑材料中的利用.广州化工, 2001, 29, (4): 21-23
[31]王守鹏.硬质PVC型材废角料的回收利用.聚氯乙烯, 1997, (2): 57-61
[32]王正熙.聚合物红外光谱分析和鉴定.成都:四川大学出版社, 1989
[33] GB/T 8814-1998,门、窗框用硬聚氯乙烯(PVC)型材
[34] Joseph H. Flynn, Leo A. Wall. A quick, direct method for the determination of activation energy from thermogravimetric data. Polymer Letter 1966, 4: 323-328
[35] Joseph H. Flynn, Leo A. Wall. Initial kinetic parameters from thermogravimetric rate and conversion data. Polymer Letter 1967, 5: 191-196
[36] Takeo Ozawa. A new method of analyzing thermogravimetric data. Bulletin of the Chemical Society of Japan. 1965, 38: 1881-1886
[37] Takeo Ozawa. Estimation of activation energy by isoconversion methods.Thermochimica Acta, 1992, 203: 159-165
[38]胡荣祖,史启帧.热分析动力学.北京:科学出版社, 2001.
[39] K.J. Laidler. The Development of the Arrhenius Equation. Journal of chemical education, 1984, 61(6): 491-498
[40]刘振海.分析化学手册,第八分册:热分析(第二版).北京:化学工业出版社, 2000.
[41] H.E.Kissinger. Reaction Kinetics in Differential Thermal Analysis Analytical Chemistry.1957, 29 :1702-1706
[42] Toop D. J. Theory of Life Testing and Use of Thermogravimetric Analysis to Predict the Thermal Life of Wire Enamels. IEEE Transaction on Electrical Insulation. 1971, EI-6: 2-14
[43] Y. N. Gupta, Amitabh Chakraborty, G. D. Pandey. Thermal and Thermooxidative Degradation of Engineering Thermoplastics and Life Estimation. Journal of Applied Polymer Science, 2004, 92: 1737–1748
[44]王培铭,许乾慰.材料研究方法.北京:科学出版, 2005
[45]柯以侃,董慧茹.分析化学手册,第三分册,光谱分析(第二版)北京:化学工业出版社, 1998
[46] K. B. ABBaS, E. M. SORVIK. On the Thermal Degradation of Poly(viny1 Chloride).111.Structural Changes During Degradation in Nitrogen. Journal of Applied Polymer Science. 1975, 19: 2991-3006
[47] D. Braun, D. Sonderhof. Assignment of UV-Absorption Maxima of Degraded PVC. Polymer Bulletin, 1985, 14: 39-43