外文翻譯--聚氯乙烯的回收（節(jié)選）

1、<p>　　中文4500字，2700單詞，15500英文字符</p><p>　　出處：Braun D. Recycling of PVC[J]. Progress in Polymer Science, 2002, 27(10):2171-2195.</p><p>　　Recycling of PVC</p><p><b>　　Abstra

2、ct</b></p><p>　　Recycling of used PVC needs a careful characterization of PVC waste. The analysis of the scrap, especially with respect to the thermal stability and the molecular weight, is useful bef

3、ore reprocessing. Additional stabilization of used PVC can be done by up to 10 wt% fillers, e.g. chalk, which does not change the mechanical properties. A literature survey on the proposed concepts and methods for materi

4、al and chemical recycling of PVC is given. q 2002 Published by Elsevier Science Ltd.</p><p>　　Keywords: Poly(vinyl chloride); Degradation; Stabilization; Material and chemical recycling</p><p>　

5、　Introduction</p><p>　　With a today’s worldwide annual production capacity of approximately more than 30 million to poly(vinyl chloride) (PVC) is the second largest volume thermoplastic only to polyethylene

6、as volume leader in the plastics industry [1]. Its ability to be compounded with many additives to a wide range of flexible and rigid products constitutes the major factor responsible for the versatile application of PV

7、C.Because of the low cost and the processability by a wide variety of techniques (e.g. calenderi</p><p>　　At the end of the service-time of these articles, large amounts of scrap arise. Therefore, the questi

8、on of the disposal of used PVC has gained increasing importance in the public discussion because of the environmental problems resulting from the rapid growth of the plastic waste during the last years.Landfilling of mun

9、icipal solid waste is becoming a burden as, for example, in the United States about80% of waste is dumped into landfills. A continuation at the present rate could exhaust the land</p><p>　　The energy recover

10、y by incineration is another way to dispose the municipal solid wastes . But environmental argumentation, such as toxic emissions from inadequate equipment or inappropriate incineration conditions, are building up a publ

11、ic resistance against these techniques. Especially, PVC incineration is connected with some technological problems due to the high chlorine content of this polymer which yields large amounts of hydrogen chloride during t

12、hermal decomposition, beside the possibili</p><p>　　installations meet with growing difficulties.</p><p>　　The recycling activities can be distinguished between chemical from material recycling.

13、 The chemical recycling is based on the idea of converting polymers back into short-chain chemicals for reuse in polymerization or other chemical processes. Four different process technologies are currently considered fo

14、r chemical recycling: cracking, gasification, hydrogenation and pyrolysis [3]. In the meantime, some commercial-scale plants are working and a number of interesting investigations with these te</p><p>　　The

15、material recycling is already practiced in plastics industry over many years with postmanufacturing waste. These experiences can be used to develop new concepts for material recycling of post-consumer waste. The major p

16、roblem in the recycling of used plastics is connected to a great inhomogeneity of the polymers</p><p>　　present in the waste [4. A statistical study by the Information System on Plastics Recycling in Western

17、 Europe shows that about 7.4% of the 9 million to of municipal solid waste in Western Europe are plastic materials. Fig. 1 shows the percentage of different polymer types in the total plastics waste.</p><p>

18、　　Fig. 1. Percentage of different polymer types in the municipal solid plastic waste.</p><p>　　The incompatibility of these components is the most important reason of the difficult processing and inferior me

19、chanical properties of the resulting products from mixed, chemically different polymers.Therefore, it is necessary to separate various polymers to boost their value. Although there are many practical problems some intere

20、sting developments for plastics waste separation were found . The separation in a hydrocyclone, which works on the principle of sorting by a centrifugal force field, u</p><p>　　In the future, a clean PVC-st

21、ream of the municipal solid wastes and from the building sector ready for material recycling can be expected. This will be accelerated by new regulations made by the governments in some countries. In Germany, the first i

22、tem of legislation to be introduced was the ‘act on the avoidance of packaging</p><p>　　waste’ ]. Its aim is to reduce the large amounts of packaging waste through avoidance and material recycling. Another f

23、act is that the manufacturers and traders are made responsible for their used packaging to relieve the local authorities of the burden to dispose the waste. In this respect, material recycling is a necessary way to reduc

24、e the municipal solid waste problem.</p><p>　　Characterization of PVC waste</p><p>　　Many different grades and types of PVC are available allowing applications as diverse as flexible sheets, pre

25、ssure pipes, transparent bottles, and medical products to be produced. For these articles, a lot of different additives and stabilizer systems are used to get suitable properties for the respective applications [5]. More

26、over, during the high temperature processing and throughout the service live of the products the polymer might be subjected to degradation . Therefore, characterization of</p><p>　　molecular weight, and cont

27、ent of additives of the individual PVC species.</p><p>　　Thermal stability</p><p>　　The main disadvantage of PVC is the rather limited thermal stability which requires addition of heat stabilize

28、rs to prevent dehydrochlorination and discolouration during processing and application. With respect to the great practical importance of the polymer, the thermal and photochemical degradation of PVC has been studied for

29、 a long time and there is a large number of published surveys . The elimination of hydrogen chloride at relatively low temperatures (about 100 ％ ) or under the influence </p><p>　　Fig. 2. Scheme of dehydroch

30、lorination of PVC.</p><p>　　The thermal stability of PVC is considerably lower than that of its low-molecular weight model analogues. Therefore, initial sites, such as allylic chlorines adjacent to internal

31、double bonds, tertiary chlorines at branched carbons, head-to-head units, and oxygen-containing structures are believed to be responsible for the instability. The mechanisms, which occur during degradation are not yet fu

32、lly understood. There are radical or ionic mechanisms suggested, and the type of reaction depends als</p><p>　　The main function of heat stabilizers is to prevent degradation during processing. They have in

33、common the ability to react with HCl when it is liberated from the polymer. Another task is to replacelabile chlorine atoms, which may initiate the dehydrochlorination of more stable groups, and thus to enhance the heat

34、stability. A number of organometallic compounds and inorganic salts are especially effective and since long time in practical use.</p><p>　　A part of the stabilizer will be consumed during processing and som

35、etimes during the application period. Therefore, the efficiency of the stabilizer system is remarkably reduced after compounding PVC with the necessary additives ] that makes it useful to get information about the residu

36、al stability of PVC articles before they can be recycled.</p><p>　　For this purpose, the determination of the thermally induced hydrogen chloride elimination from PVC seems to be the best way. The study of

37、the early stages of the reaction requires a combination of good reproducibility, high accuracy and a low detection limit. Fig. 3 shows an apparatus which is very suitable and often used for such studies since many years

38、.</p><p>　　Fig. 3. PVC degradation measuring apparatus. (a) Rotameter, (b) degradation vessel with PVC sample, (c) thermostat, (d)conductivity cell, (e) conductivity-meter and (f) computer.</p><p&

39、gt;　　The PVC-sample (,0.1 g) is introduced into the degradation vessel and then the measurement iscarried out under isothermal conditions (e.g. 180 ％ ). A stream of</p><p>　　warmed up carrier gas (nitrogen

40、or air)transports the evolved hydrogen chloride into the conductivity cell filled with distilled water. The HCl determination is performed by continuous conductometric measurements. As a result the conversiontime curve i

41、s obtained as schematically shown in Fig. 4.</p><p>　　Fig. 4. Schematic degradation curve of stabilized PVC.</p><p>　　The degradation curve of stabilized PVC shows an induction period where no H

42、Cl is evolved. During this period, the heat stabilizer is consumed and afterwards the dehydrochlorination begins. The time of induction, ti, gives an important information required to estimate the remaining stability of

43、a PVC specimen and to decide whether an additional stabilization is necessary for the material recycling. In some cases, it can be sufficient to use the simple Congo Red Test, e.g. according to DIN 53418,</p><

44、p>　　Analysis of stabilizers and other additives</p><p>　　As mentioned above, the limited thermal stability of PVC requires the use of heat</p><p>　　stabilizers in almost all fields of applica

45、tion. Besides, also other additives (e.g. light stabilizers, fillers, lubricants) are used to modify the properties of PVC or to improve its processability. At present, about 1/3 of all used PVC is plasticized by various

46、 types of modifiers [24]. Therefore, it is helpful to get some detailed information about the composition of a special PVC scrap before reuse.</p><p>　　As an example, for plasticized PVC, the analysis of PVC

47、 roofing sheets is described and show in Fig. 5 .</p><p>　　Fig. 5. Analysis of PVC roofing sheets.</p><p>　　The first step is a Soxhlet-extraction of the powdered PVC sample with diethyl ether

48、to isolate plasticizers. After evaporation of the solvent, the type and amount of plasticizer can be determined.The rest of the material is then dissolved in tetrahydrofuran (THF), and, after filtration, the fibrous mate

49、rials are obtained. The other components, insoluble in THF, are separated by a centrifuge. The remaining residue can be divided to fillers and cross-linked PVC by burning to ash. By dropping the </p><p>　　Fi

50、nally, the determination of the heat stabilizers, as an important point in the analysis of PVC waste, is particularly considered. The selection of a stabilizer system for PVC depends on many factors including application

51、, tradition of the market, and local legislation . Lead stabilizers still are the most widely used PVC heat stabilizers for some technical applications because they provide cost-effective stabilization systems and easy p

52、rocessing. They maintain volume resistivity in plasticized</p><p>　　e.g. barium–cadmium, barium–zinc, calcium–zinc. Since many years, barium–cadmium systems have been used in Europe in white window frames wi

53、th good weathering properties. But the utilization of cadmium in stabilizers or pigments recently became under increasing scrutiny. At present, all manufacturers use alternative systems such as calcium–zinc stabilizers [

54、6]. They are applied for food packaging, water bottles, and medical products. The number of applications is likely to increase with the avail</p><p>　　A simple possibility to obtain a detailed information on

55、 the stabilizer system in PVC waste can be seen in the classic analyses methods which are common practice in inorganic chemistry for the separation and determination of cations. The only difficulty is to find an easily p

56、ractical way to get the metallic cations into the water phase. For this purpose, the PVC sample can be dissolved in cyclohexanone and the received solution is used for a liquid/liquid-extraction with nitric acid containi

57、ng w</p><p>　　The determination of the metals can also be accomplished by thin layer chromatography, using an organic solution of PVC in THF [7]. Sometimes, a precipitation of the polymer might be necessary,

58、 and he remaining methanol/THF solution is used for the identification. Besides, some spectroscopic methods are described for stabilizer analysis . The infrared spectroscopy nowadays is the preferred method for this purp

59、ose because of its easy feasibility combined with a high detection rate .</p><p>　　Molecular weight</p><p>　　For different kinds of processing and various applications, industry offers PVC types

60、 with K-values between 55 and 80 [8]. The K-value is a traditional unit of measurement used until now by manufacturers to describe the molecular weight of PVC materials. This information is necessary to decide which proc

61、essing technique can be used for recycling. Also, under the influence of heat, light, and oxygen, PVC chains can be degraded or even cross-linked which results in changes in the molecular weight </p><p>　　Th

62、e simplest method for molecular weight measurements includes the determination of the viscosity of a PVC solution. The PVC is usually dissolved in</p><p>　　cyclohexanone and measured at 25 ％ , e.g. accordin

63、g to DIN 53726. For practical</p><p>　　purposes, the obtained K-value gives sufficient information in most cases. Using the Mark–Houwink equation, the molecular weight can also be alculated from the r

64、esults</p><p>　　of the viscosity measurements [9].</p><p>　　Now, the gel permeation chromatography, GPC, is by far the most popular method of molecular weight measurement . It not only gives inf

65、ormation on the molecular weight but also on the molecular weight distribution. Normally, THF is used as solvent and the columns are calibrated with polystyrene or PVC standards. In some eases, the results might be misl

66、eading, either if the investigated PVC sample is not dissolved properly or if it contains polymer that is partially insoluble due to former reatme</p><p>　　6. Conclusions</p><p>　　The studies on

67、 the recycling-ability of used PVC show the importance of a careful characterization,especially if mixed PVC from the municipal solid waste separation should be recycled. The analysis of the composition and a detailed kn

68、owledge of the heat history and the molecular weight of a PVC scrap are useful before reprocessing.</p><p>　　The suggested additional stabilization with calcium carbonate is an effective method for the recy

69、cling of PVC waste with a low remaining thermostability. The addition of chalk, up to a content of 10 phr, does not significantly change the mechanical properties, whereas it remarkably increases the heat stability.</

70、p><p>　　A number of schemes have been initiated to collect plastics and to reprocess them to useful articles. The most advantageous situation occurs when a source of a single material type can be identified, fo

71、r example, from packaging, bottles, or window profiles. Such materials can often be simply reformulated and converted into high quality products.</p><p>　　Nevertheless, new material recycling concepts for PV

72、C mixtures have to be established because in future the environmental preferences will play a larger role in the selection of a material [85]. A practical reuse of PVC requires a continuous stream of suitable scrap and t

73、he further development of technologies to reach the specifications for the intended applications. Another important point is that markets for the secondary products must exist to make the material recycling a successful

74、economic</p><p>　　References</p><p>　　[1] Engelmann M. Angew Makromol Chem 1997;244:1.</p><p>　　[2] Felger KH, editor. Kunststoff-Handbuch. Polyvinylchloride, vol. 2/1. Mu¨nche

75、n: Hanser; 1986.</p><p>　　[3] Summers JW, Mikofalvy BK, Wooton GV, Sell WA. J Vinyl Technol 1990;12:154.</p><p>　　[4] Matthews V. Plast Rubber Compos Process Appl 1993;19:197. [5] Brecker LR. Po

76、lym Prepr 1991;32(2):125.</p><p>　　[6] Freiesleben W. Role and importance of material recycling in plastics waste management during the next decade in</p><p>　　Western Europe. In: Menges G, Mich

77、aeli W, Bittner M, editors. Recycling von Kunststoffen. Mu¨nchen: Hanser; 1992.</p><p>　　[7] Mapleston P. Mod Plast Ind 1993;23(8):32.</p><p>　　[8] Holighaus R, Niemann K. Kunststoffberater

78、 1993;38(4):51. [9] Meszaros MW. Engng Plast 1992;5:335.</p><p><b>　　聚氯乙烯的回收</b></p><p>　　摘要：已用聚氯乙烯的回收利用需要對聚氯乙烯廢品的性能進行詳細的分析。在重加工之前對廢品特別是對其熱力學穩(wěn)定性和分子量進行分析是非常有用的。在不改變其機械性能的基礎上可以通過添加10％重

79、量的填料比如石粉可增加聚氯乙烯廢料的熱穩(wěn)定性。聚氯乙烯化學回收的概念和方法在2002年Elsevier Science Ltd中已經被一篇文獻提出。</p><p>　　關鍵字：聚氯乙烯（聚氯乙烯） 降解 熱穩(wěn)定性 直接回收和化學回收</p><p><b>　　1．緒論</b></p><p>　　全球范圍內聚氯乙烯的年產量接近3000萬噸，

80、在熱塑性塑料產品中僅次于PE。它能和很多的制品共混賦予了聚氯乙烯多種多樣的應用[1]。聚氯乙烯成本低，易加工，可采用多種工藝，比如砑光機擠出、注射模塑法 塑料分散體方法，再加上其優(yōu)越的物理 化學性能和耐候性，使得聚氯乙烯在很多領域內的得到應用，比如管材輪廓、地毯、電纜絕緣、屋頂薄鋼板、包裝箔、瓶子 藥品生產等[2]。</p><p>　　在這一世紀末，有許多問題出現。去年，塑料廢品快速增長，造成了很大的環(huán)境問題，

81、因此對已用聚氯乙烯的處理引起了公眾的日益注意。在美國大約80％的廢品被當作垃圾被掩埋掉，城市固體廢棄物的垃圾掩埋成為了一個主要的方法。如果照此下去，在不遠的將來垃圾掩埋將沒有地方進行下去[3]。歐洲國家同樣也面對著類似窘難的境地，因為可以利用的適宜地點是非常有限的[4]。因此垃圾掩埋越來被認為是最壞的處理垃圾廢品的方法。</p><p>　　通過焚化進行能量回收是另一種處理城市固體廢物的方法。但是由于不合適的設備

82、和不相稱的焚化條件，也會造成一些環(huán)境爭議，這樣也就增加了這些技術使用的公眾阻力。另外聚氯乙烯聚合物在熱分解時回釋放出大量HCl氣體，還能形成有毒的二惡英和呋喃。因此試圖加大這種設備的使用能力會遇到越來越大的阻力。</p><p>　　回收利用可明顯的分為化學回收和材料回收?；瘜W回收就是把聚合物轉變?yōu)槎替溁衔?，以便在以后的聚合和其他的化學反應中重新利用。化學回收又分為四個不同的工藝過程，裂縫、氣化、氫化和高溫分解

83、。通過一些大規(guī)模的工廠的運作和有意義的調查，表明這種方法是非常有效的]。最后經濟效益將決定未來每個回收工藝的應用。</p><p>　　在很多年前塑料工業(yè)已經對生產后變成廢品的材料進行循環(huán)利用了。這些經驗也可以應用的處理經過生活消費后的廢品。在重新回收塑料中最大的問題是廢品中存在著許多不同種類的聚合物。西歐的一個信息系統(tǒng)在塑料回收雜志上發(fā)表了一個統(tǒng)計分析，上面說900萬噸的市政固體中有7.4％是塑料材料。圖一表明

84、了在所有的塑料垃圾中不同聚合物類型所占的比例。</p><p><b>　　圖1</b></p><p>　　這些化合物的不相容性是加工困難和有這些不同聚合物生產出的產品機械性能低劣的最主要原因。因此很有必要把這些不同的聚合物分開以提高他們的價值。盡管其中有很多實際問題，但是塑料廢品的分離還是取得了一些很有意義的進展。由于不同聚合物密度不同，因此可以在一個旋液分離器中

85、給它們離心力，這是分離這種聚合物可行的方法[5]。當然通過不間斷的紅外分析也可以分離出常見的塑料制品，有時在分離以前，需要把聚合物中的雜質比如沙子食物紙屑等去除掉。</p><p>　　可以想象的是在將來，一條聚氯乙烯由建筑地到城市固體廢棄物的回收線在運轉。在一些國家通過政府制定新的規(guī)則可以加速這一天的到來。在德國《避免包裝浪費法》就是第一部這樣的立法，它的主要目的是通過材料的重復利用來減少大量的包裝材料的浪費，

86、另外使這些廠家和商人稱道舊包裝材料的責任，這樣減輕了地方當局的擔子，這樣材料回收是減少城市固體廢棄物的有效方法。</p><p>　　2．聚氯乙烯廢品的性能</p><p>　　許多不同的等級和類別的聚氯乙烯可以用來生產板材承壓管透明瓶子藥品。因此根據不同的用途，需要添加不同的添加劑和穩(wěn)定劑體系。另外在整個高溫加工過程和產品使用期內，聚合物要經受住熱降解。因此需要對聚氯乙烯廢品的性能比如殘

87、余穩(wěn)定性分子量添加劑含量進行有效的分析。</p><p><b>　　2.1.熱穩(wěn)定性</b></p><p>　　聚氯乙烯最大的缺點是有限的熱穩(wěn)定性，需要添加合適的熱穩(wěn)定劑，防止在加工和使用過程中脫去氯化氫和褪色。由于聚氯乙烯的熱降解和光化降解如此重要，這方面的研究很早就開始了，我們可以查到許多關于這方面的文獻和調查。聚氯乙烯聚合物在較低的溫度（大約100C）和光的

88、影響下釋放氯化氫是其分解的最基本的性質。首先這個反應生成雙鍵，其后一個所謂的急流拉鏈狀延伸到更遠的HCl上，并且形成多烯序列。這些序列由共軛雙鍵組成，鍵的平均長度為6到14nm，聚合物的顏色也變成黃色褐色，并且最后黑色。聚氯乙烯的熱穩(wěn)定性比它低分子量模型模擬系統(tǒng)低的多，因此鏈端比如連著烯丙基的氯，支鏈的三氯，頭頭鍵接結構，含氧鍵都被認為是不穩(wěn)定的原因。發(fā)生在熱分解過程中的機制還沒有完全揭示出來。不過有一些理論不如自由基和離子機制理論被提

89、出，還有在分解過程中在溫度或者氧存在的情況下的反應機理等等。</p><p><b>　　圖2</b></p><p>　　熱穩(wěn)定劑的主要作用是阻止加工期間的退化。當它們在聚合體中是它們和HCl反應，另外它們替換一些不穩(wěn)定的氯原子，而這些氯原子更容易脫去HCl，因此就提高了熱穩(wěn)定性。這些穩(wěn)定劑主要是一些有機金屬化合物和長期有效的無機鹽[6]。穩(wěn)定劑有些是在制品加工過程

90、中被使用掉，有的是在制品使用過程中被消耗掉。如果在它們重新利用前就被聚合掉那就大大的降低了穩(wěn)定體系的效率。</p><p>　　就這樣的原因，用熱的方法從聚氯乙烯中消除氯化氫似乎是最好手段。早期的研究反應的要求一個綜合好的再生性、高精度和較低檢測極限的系統(tǒng)。圖3顯示了近年來經常被用來做做這樣的研究和比較合適的儀器。</p><p><b>　　圖3</b></p

91、><p>　　聚氯乙烯樣品（0.1克）放進分解容器內，要在等溫條件下進行。分解容器內的變熱載氣（氮或空氣）運輸那氯化氫進入裝滿蒸餾水的電解池。HCl被連續(xù)的電導進行測量。就得到了如圖4的曲線。</p><p><b>　　圖4</b></p><p>　　穩(wěn)定聚氯乙烯的降解曲線顯示一誘導期，但是沒有包括HCl的。期間熱穩(wěn)定劑被消耗掉，然后開始脫去氯

92、化氫。從誘發(fā)期的時間可以知道聚氯乙烯樣品的剩余穩(wěn)定性的重要信息，并且可以得到在材料回收中添加額外的熱穩(wěn)定劑是否必要。一些情況下，剛果紅試驗就可以完成這樣的任務。</p><p>　　2.2穩(wěn)定劑和其他填料的分析</p><p>　　如上所述，由于聚氯乙烯有限的熱穩(wěn)定性，要求在幾乎所有的領域通過使用用熱穩(wěn)定劑。另外還需要其他的添加劑（例如抗光劑、補白、潤滑劑來改善聚氯乙烯的性能和加工性能。目

93、前，約三分之一的已使用聚氯乙烯是當中含有不同類型的調節(jié)劑]。因此在再使用之前需要得到聚氯乙烯碎片樣品組成的詳細情況。</p><p>　　在圖5中就給出了這樣的例子，詳細的描述和分析了增塑聚氯乙烯的屋頂薄鋼板的組成。</p><p><b>　　圖5</b></p><p>　　第一步是一索氏抽提法粉末的抽出聚氯乙烯樣品同二乙醚到隔離增塑劑。溶

94、劑蒸發(fā)以后，就可以得到增塑劑的種類和使用量。剩下的材料然后被溶于THF（四氫呋喃）中，經過二次過濾就可以得到一些纖維，那些不能溶解在四氫呋喃中的化合物用離心機進行分離。剩余的物質可以分為添加劑和交聯劑，可以通過燃燒變成灰燼。在剩余的溶解聚氯乙烯甲醇溶液滴加四氫呋喃，有沉淀析出，通過化學和分光鏡的方法可以測量出聚合物的組成。通常情況下，聚氯乙烯樣品（增塑劑、補白、聚氯乙烯它本身）主要部分的定量分析就可以給出足夠的信息。對于定性分析，紅外線

95、光譜法特別合適，因為主要的添加劑、包括共同聚合體和抗沖改性劑在內的主要物質可以顯示典型的紅外光譜]。其他的光鏡的方法也可以應用，不過樣品的制備和設備的成本比較高。</p><p>　　在參考27給出了非常具體和全面的聚氯乙烯化合物的定性分析和定量分析。最后，為聚氯乙烯化合物分析非常重要的部分，熱穩(wěn)定劑的選定是非常重要的[7]。熱穩(wěn)定劑的選定需要依據應用領域市場行情和當地的法律規(guī)定。鉛穩(wěn)定劑仍然是工程應用最廣泛的聚

96、氯乙烯熱穩(wěn)定劑，因為這個體系成本低，加工簡單。它們在增塑聚氯乙稀電纜絕緣材料中能維持一定的電阻率，對于許多通用用途來說，鉛穩(wěn)定劑是首選的熱穩(wěn)定劑，其他重要的還有金屬皂類化合物，比如鋇鎘鋇鋅鈣鋅皂類化合物，很多年來鋇鎘體系用于歐洲白色窗框，它有很好的耐候性能，但是由于鎘在穩(wěn)定劑或顏料中應用，仔細觀看就發(fā)現了不少問題。目前，所有的廠商都選擇了鈣-鋅穩(wěn)定劑29,30兩種系列]。它們用來生產食品包裝水瓶藥品，由于含又較低的有毒添加劑，所以它們的

97、應用領域越來越大。有機錫類化合物是熱穩(wěn)定劑中又一個比較大的系列。他們的性質主要是因為烷基和酯基的存在，雙烷基的鏈長越長，比如辛基錫化合物，毒性越來越低，因此可以應用到和食品接觸的材料。同時一些含硫的有機錫穩(wěn)定劑也常應用，因為它們可以提供優(yōu)越的熱穩(wěn)定性和透明性。</p><p>　　為得到穩(wěn)定劑體系在聚氯乙烯中的詳細信息 ，可以模仿一些古典的分析方法，比如無機化學中分離和分析離子的方法。真正有困難的是要找到使金屬的

98、陽離子變成那水相的簡單可行的方法。為此，可以把聚氯乙烯樣品溶解在環(huán)己酮溶液中，在相分離以后，在水中就可以得到不同的陽離子了。</p><p>　　金屬的分離也可以通過薄層色層分析法完成，這需要有機溶液的聚氯乙烯溶解在在四氫呋喃中。有時，聚合物的沉淀還是必須的，剩余甲醇／四氫呋喃解也是有用的，它們用來識別不同的聚合物。另外一些分光鏡方法需要對穩(wěn)定劑進行分析[8]。紅外光譜法仍然是現在最受歡迎的一種方法，因為它有很高

99、的分辨能力，能夠非常容易地檢測出不同的聚合物來。</p><p><b>　　2.3分子量</b></p><p>　　由于不同的加工和應用領域，工業(yè)中提出了K系數在55到80之間的商業(yè)標準。K系數很早就在應用，它用來描述聚氯乙烯分子量，一直被廠商應用。這也就決定了在材料再循環(huán)中哪些加工技術能被使用，另外，在熱 光 氧存在下聚氯乙烯鏈容易發(fā)生降解甚至交聯，這樣就導致了