ASTM_D_4818_-_21.pdf

Designation:D481821Standard 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 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2D1519 Test Methods for Rubber ChemicalsDeterminationof Melting RangeD1991 TestMethodforRubberChemicals2-Mercaptobenzothiazole(MBT)AssayD4571 Test Methods for Rubber Compounding MaterialsDetermination of Volatile MaterialD4574 Test Methods for Rubber Compounding MaterialsDetermination of Ash ContentD4936 Test Method for Mercaptobenzothiazole SulfenamideAssay by Reduction/TitrationD5044 Test Method for Rubber Compounding MaterialsFree 2-Mercaptobenzothiazole(MBT)in BenzothiazylDisulfide(MBTS)D5051 Test Method for Rubber Compounding MaterialsBenzothiazyl Disulfide(MBTS)Assay3.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.1This classification is under the jurisdiction of ASTM Committee D11 onRubber and Rubber-like Materials and is the direct responsibility of SubcommitteeD11.20 on Compounding Materials and Procedures.Current edition approved Nov.1,2021.Published November 2021.Originallyapproved in 1988.Last previous edition approved in 2017 as D4818 89(2017).DOI:10.1520/D4818-21.2For 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 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 issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.13.4 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 es