1、Designation: D4818 89 (Reapproved 2012)Standard Classification forRubber Compounding MaterialsVulcanizationAccelerators1This standard is issued under the fixed designation D4818; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This classification covers vulcanization accelerators anddefines their important chemical and physical charact
3、eristics.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 D1519, D4571, D4572 and D4574, formeasurement of these properties, are not yet adapted for thevulcanizat
4、ion 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:2D1519 Test Methods for Rubber ChemicalsDet
5、ermination of Melting RangeD4571 Test Methods for Rubber Compounding MaterialsDetermination of Volatile MaterialD4572 Test Method for Rubber ChemicalsWet SieveAnalysis of SulfurD4574 Test Methods for Rubber Compounding MaterialsDetermination of Ash Content3. Significance and Use3.1 Class 1, Sulfenam
6、ides:3.1.1 As a group, the 2-benzothiazyl 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 tempe
7、ratures. Thedelay avoids premature 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
8、 can affect their performance characteristics.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 h
9、umidity, and the impurity profile 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 inductionper
10、iod.3.2 Class 2, ThiazolesThiazole 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 thi
11、ck-sectioned goods, because of a 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
12、 thiazole-guanidine combinations 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
13、for other accelera-tors.3.5 Class 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,
14、thiurams arenormally used in combination 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.
15、 Di,1This classification is under 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, 2012. Published July 2012. Originally approvedin 1988. Last previous edition approved in 20
16、05 as D4818 89 (2005). DOI:10.1520/D4818-89R12.2For referenced 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 AST
17、M International, 100 Barr Harbor Drive, PO Box C700, West 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,
18、 ofthese materials may affect their use as vulcanization accelera-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 Cl
19、ass 3Guanidines,4.1.4 Class 4Dithiocarbamates,4.1.5 Class 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 dep
20、ending on the nature ofsubstitution around the sulfenamide 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
21、hydrogen on the sulfenamide nitrogen, inaddition to the generic 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 c
22、arbon attachments,each with at least two hydrogens on the 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 tw
23、o secondary carbon attach-ments to the sulfenamide nitrogen. 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-Mercaptob
24、enzothiazole (MBT)See Fig. 4.5.2.2 Zinc Salt of 2-Mercaptobenzothiazole (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 of guani-dines in comm
25、on use. They both show a similar vulcanizationefficiency.5.3.1 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
26、Unhindered Secondary AminesFIG. 3 Sulfenamides of Hindered Secondary AminesFIG. 4 2-Mercaptobenzothiazole (MBT)FIG. 5 Zinc Salt of 2-Mercaptobenzothiazole (ZMBT)D4818 89 (2012)25.4 Dithiocarbamates:where:R8 = alkyl groups such as amyl, butyl, ethyl or methyl, oraryl groups such as phenyl or benzyl;R
27、9 = alkyl groups such as amyl, butyl, ethyl or methyl, oraryl 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 telluriu
28、m or selenium.5.5 Thiuram Disulfides:where:R8 =R9 = alkyl 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 = p
29、henyl: dimethyl diphenyl thiuramsulphide (DMPTD).5.5.1 Dipentamethylene 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 monosulph
30、ide (DPTM),n = 2: dipentamethylene thiuram tetrasulphide (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 properti
31、es is important in maintainingconsistent end-product performance.6.2 Initial Melting PointA determination of the initialmelting point shall be done in accordance with Test MethodD1519. The initial melting point can be an indication ofrelative purity of the accelerator. If the accelerator containssig
32、nificant levels of other materials that are mutually soluble 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,hig
33、hly crystalline, or polar organic molecules, or both, may 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
34、only important for materialswith melting points that are 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 requi
35、res a relatively fine and easilydispersed physical form. 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-
36、Tolyl Biguanidine (OTBG)FIG. 10 Dipentamethylene Thiuram Disulphide (DPTD)D4818 89 (2012)36.4 Percent AshA determination of the amount of non-combustibles shall be conducted in accordance with a modifi-cation of Test Method D4574. Inorganic materials (ash) areoccasional contaminants in vulcanization
37、 accelerators, andthey may cause problems since they ordinarily 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 s
38、alts).6.5 Percent Loss on HeatingA measure of the amount ofheat loss of the accelerator shall be conducted in accordancewith a modification of Test Method D4571. The heat loss of theaccelerators (except sulfenamides) is nearly identical with themoisture content. Excess moisture in a rubber mixture m
39、aycause problems during vulcanization since water is 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 becaus
40、ed by hydrolysis reactions.6.7 Percent Insolubles in 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 sulfenam
41、ide degradation as describedin 4.1.3. MBTS is also a 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,
42、and it can consequentlybe detected by measuring the amount 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-m
43、ance characteristics, such as scorch time and cure efficiency,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 ami
44、ne.6.8.2 Assay for MBT.6.8.3 Assay for MBTS.6.8.4 Assay 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 impor
45、tant because of the effect of MBT on scorch safety.6.10 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 asimpuritie
46、s in the accelerator.6.11 DispersibilityA determination 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 valid
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