ASTM_D_4818_-_89_2012.pdf

Designation:D481889(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 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 characteristics.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 thevulcanization 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 ChemicalsDeterminationof 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,Sulfenamides: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 temperatures.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 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 humidity,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 inductionperiod.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 thick-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 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 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,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 are1This 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 2005 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 used 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 chemical or physical charac