1、Designation: D 4818 89 (Reapproved 2005)Standard Classification forRubber Compounding MaterialsVulcanizationAccelerators1This standard is issued under the fixed designation D 4818; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This classification covers vulcanization accelerators anddefines their important chemical and physical char
3、acteristics.The properties outlined herein are useful for quality control;they can frequently be directly or indirectly related to theperformance characteristics in rubber compounds.1.2 Test Methods D 1519, D 4571, D 4572 and D 4574, formeasurement of these properties, are not yet adapted for thevul
4、canization accelerators. Draft methods are being developedand will be submitted through Subcommittee D11.11 forprocessing and approval. A discussion of the reasons fordetermining these properties is contained in Section 6.2. Referenced Documents2.1 ASTM Standards:2D 1519 Test Method for Rubber Chemi
5、calsMeltingRangeD 4571 Test Methods for Rubber ChemicalsDetermination of Volatile MaterialD 4572 Test Method for Rubber ChemicalsWet SieveAnalysis of SulfurD 4574 Test Methods for Rubber ChemicalsDetermination of Ash Content3. Significance and Use3.1 Class 1, Sulfenamides:3.1.1 As a group, the 2-ben
6、zothiazyl sulfenamides are theprinciple sulfur vulcanization accelerators used in the rubberindustry today. The role of these materials in vulcanization isdual. They provide scorch time (delay period) in the crosslink-ing or vulcanization operation at processing temperatures. Thedelay avoids prematu
7、re crosslinking during the processing, forexample, mixing, extrusion, etc. Once the mixed rubber is atthe curing temperature, these materials promote a rapid rate ofcuring (crosslinking, vulcanization).3.1.2 The presence of certain impurities in this class ofmaterials can affect their performance ch
8、aracteristics.3.1.3 The 2-benzothiazyl sulfenamides are subject to deg-radation on extended storage. Significance degradation canaffect their performance characteristics. In particular, the qual-ity of the material is a function of storage time, temperature,relative humidity, and the impurity profil
9、e of the material; forexample, free amines, salts of 2-mercaptobenzothiazole, etc.Since sulfenamide degradation in storage is an autocatalyticprocess (degradation products accelerate further degradation),significant degradation may only occur after a long inductionperiod.3.2 Class 2, ThiazolesThiazo
10、le derivatives are versatilevulcanization accelerators that are widely used in the rubberindustry either alone or in combination with other accelerators.3.3 Class 3, GuanidinesThe guanidines have little impor-tance as primary vulcanization accelerators, except for thick-sectioned goods, because of a
11、 typically slow vulcanization rate.As secondary accelerators they are used with other acceleratorsof the thiazole class. These resulting combinations vulcanizefaster and give higher levels of vulcanization than do theirindividual constituents when used separately. The thiazole-guanidine combinations
12、 are frequently used for technicalrubber goods.3.4 Class 4, DithiocarbamatesVulcanization with dithio-carbamates is faster than with thiurams. Dithiocarbamates areused as ultra accelerators with normal sulfur levels. They arealso employed as secondaries or activators for other accelera-tors.3.5 Clas
13、s 5, Thiurams (disulfides)Thiuram disulfide ac-celerators are used for vulcanization without elemental sulfurto produce rubber compounds that show essentially no rever-sion and that have low compression set and good agingcharacteristics. For low sulfur vulcanization, thiurams arenormally used in com
14、bination with sulfenamides. With anormal amount of sulfur, thiurams act as ultra accelerators.3.6 Class 6, Thiurams (other than disulfides)This classcontains other thiuram types that are not disulfides. They areused as ultra accelerators with normal amounts of sulfur. Di,1This classification is unde
15、r the jurisdiction of ASTM Committee D11 onRubber and is the direct responsibility of Subcommittee D11.20 on CompoundingMaterials and Procedures.Current edition approved May 1, 2005. Published May 2005. Originallyapproved in 1988. Last previous edition approved in 1999 as D 4818 88(1999).2For refere
16、nced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West
17、Conshohocken, PA 19428-2959, United States.tetra, and hexasulfides can be employed without sulfur or withlow sulfur levels to obtain rubber compounds with muchreduced reversion tendencies.3.7 The chemical or physical characteristics, or both, ofthese materials may affect their use as vulcanization a
18、ccelera-tors.4. Basis of Classification4.1 The accelerators are divided into six classes accordingto their chemical structure and application in the rubberindustry. They are as follows:4.1.1 Class 1Sulfenamides,4.1.2 Class 2Thiazoles,4.1.3 Class 3Guanidines,4.1.4 Class 4Dithiocarbamates,4.1.5 Class
19、5Thiurams (disulfides), and4.1.6 Class 6Thiurams (other than disulfides).5. Basic Description of Accelerators5.1 SulfenamidesCompounds designated as2-benzothiazyl sulfenamides vary in chemical nature andgeneral performance characteristics depending on the nature ofsubstitution around the sulfenamide
20、 nitrogen. The sulfenamidenitrogen is the nitrogen atom that is outside of the ring in thestructures given below. There are three fundamental types incommon use, as follows:5.1.1 Sulfenamides of Primary Amines (Type I)Thesecompounds have one hydrogen on the sulfenamide nitrogen, inaddition to the ge
21、neric R group. In general, this type, as agroup, exhibits a somewhat shorter scorch time and higher curerate than the other sulfenamides (see Fig. 1).5.1.2 Sulfenamides of Unhindered Secondary Amines (TypeII)These compounds have two primary carbon attachments,each with at least two hydrogens on the
22、carbon bonded to thesulfenamide nitrogen. In this case, X can be one or two. Thistype, as a group, exhibits an intermediate scorch time and curerate (see Fig. 2).5.1.3 Sulfenamides of Hindered Secondary Amines (TypeIII)These compounds have two secondary carbon attach-ments to the sulfenamide nitroge
23、n. This type, as a group,exhibits a longer scorch time and lower cure rate than the othersulfenamides (see Fig. 3).5.2 ThiazolesThere are three different thiazoles in com-mon use. They all show a similar vulcanization effect.5.2.1 2-Mercaptobenzothiazole (MBT)See Fig. 4.5.2.2 Zinc Salt of 2-Mercapto
24、benzothiazole (ZMBT)Thiszinc salt may consist of different substances, but it is generallycharacterized as illustrated in Fig. 5.5.2.3 Dibenzothiazyldisulfide (MBTS)See Fig. 6.5.3 GuanidinesThere are two different types ofguanidines in common use. They both show a similar vulca-nization efficiency.5
25、.3.1 Symmetric (Type I):5.3.1.1 Diphenylguanidine (DPG)See Fig. 7.5.3.1.2 Di-Ortho-Tolylguanidine (DOTG)See Fig. 8.5.3.2 Asymmetric (Type II), Ortho-Tolylbignanidine(OTBG)See Fig. 9.FIG. 1 Sulfenamides of Primary AminesFIG. 2 Sulfenamides of Unhindered Secondary AminesFIG. 3 Sulfenamides of Hindered
26、 Secondary AminesFIG. 4 2-Mercaptobenzothiazole (MBT)FIG. 5 Zinc Salt of 2-Mercaptobenzothiazole (ZMBT)D 4818 89 (2005)25.4 Dithiocarbamates:where:R8 = alkyl groups such as amyl, butyl, ethyl or methyl, oraryl groups such as phenyl or benzyl;R9 = alkyl groups such as amyl, butyl, ethyl or methyl, or
27、aryl groups such as phenyl or benzyl;M = metals such as zinc, tellurium, copper, cadmium,tellurium, nickel, bismuth, or lead; andn = 2 in the case of zinc, copper, cadmium, nickel, andlead;3 in the case of bismuth; and4 in the case of tellurium or selenium.5.5 Thiuram Disulfides:where:R8 =R9 = alkyl
28、 group,R8 = alkyl group,R9 = aryl group, andR8R9 = cyclic group.R8 =R9 methyl: tetramethyl thiuram disulphide(TMTD),R8 =R9 = ethyl: tetraethyl thiuram disulphide (TETD),R8 =R9 = butyl: tetrabutyl thiuram disulphide (TBTD),andR8 = methyl R9 = phenyl: dimethyl diphenyl thiuramsulphide (DMPTD).5.5.1 Di
29、pentamethylene Thiuram Disulphide (DPTD)SeeFig. 10.5.6 Thiurams (Monosulfides and Polysulfides):5.6.1 Monosulfides:where:R8 =R9 = methyl: tetramethyl thiuram monosulphide(TMTM).5.6.2 Polysulfides:where:n = 1: dipentamethylene thiuram monosulphide (DPTM),n = 2: dipentamethylene thiuram tetrasulphide
30、(DPTT), andn = 6: dipentamethylene thiuram hexasulphide (DPTH).6. Composition and Properties6.1 The following properties of the accelerators are judgedto be most significant in terms of their performance in rubber.The control of these properties is important in maintainingconsistent end-product perf
31、ormance.6.2 Initial Melting PointA determination of the initialmelting point shall be done in accordance with Test MethodD 1519. The initial melting point can be an indication ofrelative purity of the accelerator. If the accelerator containssignificant levels of other materials that are mutually sol
32、uble inthe accelerator, a significant lowering of the melting pointoccurs. For example, this occurs when the sulfenamide hasundergone appreciable degradation, as discussed in 4.1.3.Many inorganic impurities and certain high molecular weight,highly crystalline, or polar organic molecules, or both, ma
33、y notdepress the initial melting point significantly. Consequently,the melting point is not an absolute indicator of purity (notapplicable to all dithiocarbamates since some of them melt attemperatures over 300C).6.3 Wet Sieve TestThis test is only important for materialswith melting points that are
34、 higher than the rubber compoundmixing temperatures. To efficiently accelerate vulcanization,the accelerator must disperse uniformly in the rubber duringmixing and dissolve at vulcanization temperatures. For highmelting accelerators, this requires a relatively fine and easilydispersed physical form.
35、 A wet screen test is an indication ofthis property. The test cannot be used, however, with physicalforms other than powders.FIG. 6 Dibenzothiazyldisulfide (MBTS)FIG. 7 Diphenyl Guanidine (DPG)FIG. 8 Di-Ortho-Tolyl Guanidine (DOTG)FIG. 9 Ortho-Tolyl Biguanidine (OTBG)FIG. 10 Dipentamethylene Thiuram
36、 Disulphide (DPTD)D 4818 89 (2005)36.4 Percent AshA determination of the amount of non-combustibles shall be conducted in accordance with a modifi-cation of Test Method D 4574. Inorganic materials (ash) areoccasional contaminants in vulcanization accelerators, andthey may cause problems since they o
37、rdinarily will not dissolvein rubbers. Transition metals such as iron, copper, and manga-nese, especially in soluble form, may have a detrimental effecton the oxidative stability of the rubber (not applicable todithiocarbamates, which are metal salts).6.5 Percent Loss on HeatingA measure of the amou
38、nt ofheat loss of the accelerator shall be conducted in accordancewith a modification of Test Method D 4571. The heat loss ofthe accelerators (except sulfenamides) is nearly identical withthe moisture content. Excess moisture in a rubber mixture maycause problems during vulcanization since water is
39、vaporized,which may produce porosity in the cured vulcanizate.6.6 Percent Moisture in SulfenamidesA determination ofmoisture content in sulfenamides is essential, since the degra-dation of sulfenamides in storage, as discussed in 4.1.3, can becaused by hydrolysis reactions.6.7 Percent Insolubles in
40、SulfenamidesAdetermination ofinsolubles in sulfenamides is important, since 2-benzothiazyldisulfide (MBTS) may be present in benzothiazole sulfenamideaccelerators as a by-product of the manufacturing process or asa result of benzothiazole sulfenamide degradation as describedin 4.1.3. MBTS is also a
41、vulcanization accelerator. However, ithas much less delay than the sulfenamides, and appreciablelevels of MBTS can cause scorch problems in rubber manu-facturing operations. MBTS is much less soluble in someorganic solvents than the sulfenamides, and it can consequentlybe detected by measuring the a
42、mount of material that does notdissolve in an appropriate solvent.6.8 AssayA measurement of the amount of the specifiedchemical entity in the accelerator by an assay is required, sincethe purity of the accelerator can affect vulcanization perfor-mance characteristics, such as scorch time and cure ef
43、ficiency,as well as storage stability. Not all impurities have equaldetrimental effects on the performance of the accelerator. Atthe present time, there is no single test that measures all of theimpurities.6.8.1 Assay for sulfenamides and free amine.6.8.2 Assay for MBT.6.8.3 Assay for MBTS.6.8.4 Ass
44、ay for guanidines.6.8.5 Assay for dithiocarbamates.6.8.6 Assay for thiurams (disulfides).6.8.7 Assay for thiurams (other than disulfides).6.9 Percent Free MBTA determination of free2-mercaptobenzothiazole in dibenzothiazyl disulfide (MBTS)is important because of the effect of MBT on scorch safety.6.
45、10 Percent Metal ContentA determination of the metalcontent in ZMBT and dithiocarbamates is important. It givesonly a relative indication of the content of active matter, sincesmall quantities of free metal salts are invariably present asimpurities in the accelerator.6.11 DispersibilityA determinati
46、on of the dispersibility ina rubber compound is essential, since the accelerators, both inpowder or pellet form, must disperse uniformly in a rubbercompound to achieve optimal vulcanization.ASTM International takes no position respecting the validity of any patent rights asserted in connection with
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