1、Designation: D4818 89 (Reapproved 2017)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、erminationof 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, Sulfenami
6、des: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 temper
7、atures. 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 hu
9、midity, 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 inductionperi
10、od.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 thic
11、k-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 f
13、or 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, t
14、hiurams 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 are1This classification is under the jurisdiction of ASTM Com
15、mittee D11 onRubber and Rubber-like Materials and is the direct responsibility of SubcommitteeD11.20 on Compounding Materials and Procedures.Current edition approved Feb. 1, 2017. Published March 2017. Originallyapproved in 1988. Last previous edition approved in 2012 as D4818 89 (2012).DOI: 10.1520
16、/D4818-89R17.2For 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.Copyright ASTM International, 100 Barr Harbor Dr
17、ive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations i
18、ssued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1used as ultra accelerators with normal amounts of sulfur. Di,tetra, and hexasulfides can be employed without sulfur or withlow sulfur levels to obtain rubber compounds with muchreduced reversion tendencies.3.7 The che
19、mical or physical characteristics, or both, 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 1S
20、ulfenamides,4.1.2 Class 2Thiazoles,4.1.3 Class 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
21、 andgeneral performance characteristics depending 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 Prim
22、ary Amines (Type I)Thesecompounds have one 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
23、 (TypeII)These compounds have two primary carbon 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 Second
24、ary Amines (TypeIII)These compounds have two 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 sim
25、ilar vulcanization effect.5.2.1 2-Mercaptobenzothiazole (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
26、 two different types of guani-dines in common 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. 9.5.4 Dithiocarbama
27、tes:FIG. 1 Sulfenamides of Primary AminesFIG. 2 Sulfenamides of Unhindered Secondary AminesFIG. 3 Sulfenamides of Hindered Secondary AminesFIG. 4 2-Mercaptobenzothiazole (MBT)FIG. 5 Zinc Salt of 2-Mercaptobenzothiazole (ZMBT)FIG. 6 Dibenzothiazyldisulfide (MBTS)FIG. 7 Diphenyl Guanidine (DPG)D4818 8
28、9 (2017)2where:R = alkyl groups such as amyl, butyl, ethyl or methyl, oraryl groups such as phenyl or benzyl;R“ = 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 =
29、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:R =R“ = alkyl group,R = alkyl group,R“ = aryl group, andRR“ = cyclic group.R =R“ methyl: tetramethyl thiuram disulphide (TMTD),R =R“ = ethyl: tetra
30、ethyl thiuram disulphide (TETD),R =R“ = butyl: tetrabutyl thiuram disulphide (TBTD),andR = methyl R“ = phenyl: dimethyl diphenyl thiuram sul-phide (DMPTD).5.5.1 Dipentamethylene Thiuram Disulphide (DPTD)SeeFig. 10.5.6 Thiurams (Monosulfides and Polysulfides):5.6.1 Monosulfides:where:R=R“ = methyl: t
31、etramethyl thiuram monosulphide(TMTM).5.6.2 Polysulfides:where:n = 1: dipentamethylene thiuram monosulphide (DPTM),n = 2: dipentamethylene thiuram tetrasulphide (DPTT), andn = 6: dipentamethylene thiuram hexasulphide (DPTH).6. Composition and Properties6.1 The following properties of the accelerator
32、s are judgedto be most significant in terms of their performance in rubber.The control of these properties 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
33、 melting point can be an indication ofrelative purity of the accelerator. If the accelerator containssignificant 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 apprec
34、iable degradation, as discussed in 4.1.3.Many inorganic impurities and certain high molecular weight,highly 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 t
35、o 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 higher than the rubber compoundmixing temperatures. To efficiently accelerate vulcanization,the accelerator must disperse uniformly in the
36、rubber duringmixing and dissolve at vulcanization temperatures. For highmelting accelerators, this requires 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.6.4 Percent Ash
37、A 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 accelerators, andthey may cause problems since they ordinarily will not dissolvein rubbers. Transition m
38、etals such as iron, copper, andmanganese, especially in soluble form, may have a detrimentaleffect on the oxidative stability of the rubber (not applicable todithiocarbamates, which are metal salts).6.5 Percent Loss on HeatingA measure of the amount ofheat loss of the accelerator shall be conducted
39、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 mayFIG. 8 Di-Ortho-Tolyl Guanidine (DOTG)FIG. 9 Ortho-Tolyl Biguanidine (OTBG)FIG. 10 Dipentamethylene Thiur
40、am Disulphide (DPTD)D4818 89 (2017)3cause 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,
41、 as discussed in 4.1.3, can becaused by hydrolysis reactions.6.7 Percent Insolubles in SulfenamidesA determination ofinsolubles in sulfenamides is important, since 2-benzothiazyldisulfide (MBTS) may be present in benzothiazole sulfenamideaccelerators as a by-product of the manufacturing process or a
42、sa result of benzothiazole sulfenamide 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 someorgan
43、ic solvents than the sulfenamides, 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 accelerato
44、r can affect vulcanization perfor-mance 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
45、Assay for sulfenamides and free amine.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 dibe
46、nzothiazyl disulfide (MBTS)is important 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
47、 are invariably present asimpurities 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 tak
48、es no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own re
49、sponsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldm
