ASTM_D_7997_-_21.pdf

Designation:D799721Standard Practice forPolyurethane Raw Materials:Gel Tests for PolyurethaneNon-Foam Formulations1This standard is issued under the fixed designation D7997;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 practice covers procedures for determining the geltimes of polyurethane non-foam formulations using commer-cially available gel test equipment.1.2 Definitions,terms,and techniques are described alongwith procedures for calculating sample weights.1.3 The values stated in SI units are to be regarded asstandard.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.NOTE1There is no known ISO equivalent to this standard.1.5 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:2D883 Terminology Relating to Plastics3.Terminology3.1 DefinitionsFor general definitions of terms used in thispractice see Terminology D883.3.2 Definitions of Terms Specific to This Standard:3.2.1 gel pointthe extent of polymerization at which theupper limit,as defined by the procedure being run,is reached.3.2.2 gel timethe time from the initiation of the reaction tothe gel point.3.2.3 resin blend(formulated polyol)complete ingredientformulation without the isocyanate component.3.2.4 indexthe ratio of the equivalents of the isocyanatecomponent to the equivalents of the resin blend of a polyure-thane formulation.4.Summary of Practice4.1 The gel time of a polyurethane non-foam formulation isdetermined by measuring the time required for the viscosity ofthe polymerizing system to increase to a set level using a gelmeter.It is recommended that the torque of the gel meter beverified with a gauge certified to NIST standards.5.Significance and Use5.1 General Utility:5.1.1 This practice is suitable for research,quality control,specification testing and process control.5.1.2 It is useful to define and verify the reactivity ofnon-foam polyurethane formulations.5.2 Limitations:5.2.1 Operator-to-operator variability and lab-to-lab vari-ability can be significant.5.2.2 The variability of this practice is dependent on theequipment used to measure the gel time.It is recommendedthat the testing laboratory and the client agree on the equipmentand the conditions to be used that include the following:5.2.2.1 Gel Tester and gel point criteria,5.2.2.2 Speed/rpm of the mixer,5.2.2.3 Type and shape of the mix blades,5.2.2.4 Size and type(for example,shape,lined or unlined)of container for mixing the components and for measuring thegel time,and5.2.2.5 The volume(or height)of material to be placed inthe container for measuring the gel time and the depth of themeasuring wire or spindle of the gel tester from the bottom ofthe container.5.2.3 Users of this practice shall develop their own precisiondata to determine if these procedures meet their requirements.5.2.4 It is possible that low-levels(ppm,ppb)of contami-nants will not be detected using this practice.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.22 on Cellular Materials-Plastics and Elastomers.Current edition approved Jan.15,2021.Published January 2021.Originallyapproved in 2015.Last previous edition approved in 2015 as D7997-15.DOI:10.1520/D799721.2For 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.16.Sampling6.1 Since organic isocyanates react with atmosphericmoisture,take special precautions in sampling.Usual samplingmethods,even when conducted rapidly,can cause contamina-tion of the sample with insoluble urea.Therefore,blanket thesample with dry air or nitrogen at all times.(WarningDiisocyanates are eye,skin and respirator