AIAA 2001-3281 Methodology for Evaluating Raw Material Changes to RSRM Elastomeric Insulation Materials S. Mildenhall Thiokol Propulsion Brigham City, UT AIAA/ASME/SAE/ASEE Joint 37 th Propulsion Conference and Exhibit 8-11 July 2001 Salt Lake City, Utah For permission to copy or to republish, contact the copyright owner named on the first page. For AIAA-held copyright, write to AIAA Permissions Department, 1801 Alexander Bell Drive, Suite 500, Reston, VA, 20191-4344. AIAA 2001-3281 METHODOLOGY FOR EVALUATING RAW MATERIAL CHANGES TO RSRM ELASTOMERIC INSULATION MATERIALS Scott D. MildenhaU Senior Principle Engineer Thiokol Propulsion Brigham City, UT Abstract manufacturers going out of business or being bought-out, or the need for new manufacturing The Reusable Solid Rocket Motor (RSRM) uses equipment or facilities. Usually the amount of an asbestos and silicon dioxide filled acrylonitrile elastomeric raw material used on the RSRM is butadiene rubber (AS-NBR) as the primary internal comparatively small and efforts to influence a insulation to protect the case from heat. During the manufacturer to not make a change are futile. course of the RSRM Program, several changes have been made to the raw materials and processing of the Changes to elastomeric insulation raw materials have AS-NBR elastomeric insulation material. These proven to be inevitable and repeating. Changes have changes have been primarily caused by raw materials affected each of the Reusable Solid Rocket Motor becoming obsolete. In addition, some process changes (RSRM) elastomeric insulation materials. This have been implemented that were deemed necessary to document focuses on the changes that have been made improve the quality and consistency of the AS-NBR to the primary RSRM internal insulation material, insulation material. Each change has been evaluated asbestos and silicon dioxide filled acrylonitrile using unique test efforts customized to determine the butadiene rubber (AS-NBR). These changes range potential impacts of the specific raw material or process from simply upgrading a raw material manufacturer's change. Following the evaluations, the various raw production line to completely changing from an material and process changes were successfully obsolete raw material to a new, chemically different, implemented with no detectable effect on the replacement raw material. Typically when an performance of the AS-NBR insulation. This paper obsolescence issue is identified, a reserve or stockpile will discuss some of the raw material and process of the raw material ispurchased to ensure adequate changes evaluated, the methodology used in designing time to identify and evaluate a replacement. However, the unique test plans, and the general evaluation results. due to the obsolescent nature of some of these changes, A summary of the change history of RSRM AS-NBR frequently little time is available to evaluate the change. internal insulation is also presented. AS-NBR insulation is ordered from one qualified manufacturer that has supplied this material throughout Introduction the shuttle solid rocket motor program. The long-term working relationship established between this supplier The space shuttle reusable solid rocket motor (RSRM) and Thiokol has greatly enhanced the ability to program faces many material change and obsolescence communicate and evaluate raw material change issues. issues. Because the RSRM is part of the manned space AS-NBR insulation is mixed in a Banbury® type flight shuttle system, these changes typically require internal mixer, and calendered into sheet stock. extensive side-by-side testing and verification prior to Extruded AS-NBR parts are also made for regions of implementation. It is critical that the erosion, the RSRM that require unique pre-formed structural, bonding, and processing characteristics of configurations. the elastomeric insulation materials be maintained. AS-NBR is the primary internal insulation material in Obsolescence issues are caused by any of several the RSRM, and is also used to fabricate the igniter factors including, discontinued products due to poor insulation and nozzle flexible boot. The ID surfaces of sales, changing environmental regulations, RSRM case segments are coated with Chemlok® 1 American Institute of Aeronautics and Astronautics Copyright©2001byThiokolPropulsion,ADivisionofCordantTechnologies,Inc. PublishedbvtheArnericanInstituteofAeronauticsandAstronautics.lnc.withpermission vulcanizatiaodnhesiveGs.reeonruncureAdS-NBR insulatiomnateriarlseachadesiretemperature-time insulatioinslaidagainsthteseadhesivceoatesdurfaces profilebeforecompletinthgecurecycle. usingmultiplelayerosfsheesttockuntilthedesired thicknesissattainedA.S-NBRextrusionasrealso installeidnsomeregionosfthesegmentTsh.e Summary of Changes to AS-NBR Insulation insulatiolnay-upiscoverewdithareleasceloth, breathecrlothmateriaal,ndavacuumbag.The The following table lists the changes that have occurred segmenatrsecuredundevracuuminalargeautoclave to AS-NBR internal insulation. An approximate date is at100psiandtemperatuorfe290°F.Embedded listed for each change to establish the chronological thermocoupaleresmonitoretodensurtehatthe order of the changes. Selected changes will be discussed in further detail. Summary of Changes to AS-NBR Insulation Title of Change Date Description of Change New Mixer 1980s A new 500 lb capacity Banbury® type internal mixer was purchased by the AS-NBR manufacturer to replace the 400 lb capacity mixer as the primary mixer. The 400 Ib mixer was retained as a backup mixer. New Calender 1980s A new calender was purchased by the AS-NBR manufacturer. The old calender was retained as a backup. Altax® Accelerator 1987 The original manufacturer of Altax® accelerator discontinued making this accelerator. The distributor elected to continue to market Altax® accelerator under the same brand name, but from a different manufacturer. Kadox® 930C Zinc Oxide 1993 Kadox® 930C zinc oxide was selected to replace Protox® 166 zinc oxide, which was discontinued. Agerite Stalite S® 1993 Agerite Stalite S® was selected to replace Agerite White®, Antioxidant which was discontinued. HiSil® 233 Silicon 1993 The alkali source used in the manufacture of silica was changed Dioxide from caustic soda to soda ash. 1994 Due to environmental concerns associated with the use of soda ash, the silica manufacturer changed the alkali source from soda ash to caustic soda. 1996 The silica manufacturer constructed a second sodium silicate furnace. The new furnace uses soda ash as the alkali source. The old furnace was still using caustic soda as its alkali source. Silica from both furnaces could be blended. Harwick® F-1500 Stearic 1997 Harwick® F-1500 stearic acid was selected to replace Acid Hydrofol® 1800B stearic acid, which was discontinued. Picco® 6100 Resin 1997 A new manufacturing line was built for the production of Tackifier Picco® 6100 resin, which is used to increase the build tack of the uncured AS-NBR insulation. Sulfur Oil 1999 The sulfur manufacturer approved a new oil source. Oil is added to the powdered sulfur to prevent dust hazards, and to enhance dispersion durin_ mixin[_. Sulfur Masterbatch 1999 A refining step was added to the fabrication process of the sulfur Refining masterbatch to eliminate sulfur clumps. Sulfur Masterbatch 2000 Three 50-pound sulfur masterbatches are crossblended to Crossblending improve the overall uniformity of the masterbatch and to reduce the cost of analysis of the masterbatches. Previously each 50-pound sulfur masterbatch was processes and tested separately. 2 American Institute of Aeronautics and Astronautics TheAS-NBRmanufactuhrearssubmitteodthecrhange notificationinsdicatinagchangienthemanufactuorefr -Specifihceat arawmateriaTl.hesearefrequentdlyeterminetodbe -Thermaclonductivity onlyachangienownershoipfacompanoyrownership ofaproductiofancilityandnottruechangetostheraw Qualificatiotenstsareusedtoevaluatcehangebsu,t materiaIl.nordetrobetteurnderstaannddcontrothl ese maynotbesufficientot fullycharacteriazespecific typesofchangetsh,eAS-NBRmanufactucreurrrently changeT.heAS-NBRspecificatioanlsoallowsfor documen(tosntheirrawmateriaslpecificationthse) otheardditionatelstsasrequiretdoverifythatthe suppliearndthelocationwheretherawmateriaalsre materiaislsuitablfeortheenduse.Inmostsituations manufactureTdh.eAS-NBRsupplieprurchasmesany additiontaelstsareaddefdoramorecompletcehange rawingredienftrsommajorrubbecrhemicsaul ppliers evaluationT.heseadditiontaelstsmayincludebond (ordistributorso)n;lyafewrawmateriaalsrebought testss,ub-scahleotfiretestsa,ccelerataegding directlyfromthemanufactureDro.cumentatoioftnhe tensile/elongatteiosntsa,ndaccelerataegdingbond locatioonfmanufacturiinsgalsorequireodnraw testsD. ataforcomparisofonrtheseadditionatelsts materiasluppliecrertificationsT.hisdocumentation maybelimiteds,oacontrotlestistypicallyrun.Also changweasimplementaefdterarawmateriaslupplier lot-to-lovtariatioonfqualityconformandcaetarequires senstulfurthatwasmanufacturaetdadifferent theuseofacontroslamploenevaluatiotensts.The locationT.henewsulfurw, hichmetthesulfur controml ateriaislpreferabmlyixedatthesametimeas suppliers'specificatiorne,sulteidnclumpinogfthe theevaluatiomnateriaulsingallofthesamelotsofraw sulfudruringamasterbatmchixingoperationT.he materialesx,cepftortherawmateriableingchanged. sulfucrlumpdsidnotdispersdeuringthesubsequent Thecontroml ateriaislalsousedthroughotuhtetesting mixingprocessaensdresulteidnsmalhlardsulfur-rich tohelpverifythatspecimepnreparatioanndtest blackspotsinthecuredAS-NBRinsulator. proceduraerseproperlcyonducted. Test Methods Used to Evaluate Raw Material Changes Material Samples Used in Raw Material Change Evaluations The AS-NBR insulation specification requires that the following tests be conducted by the manufacturer on Changes are typically evaluated first on the new and old each lot of material as quality conformance inspection raw materials, particularly if the replacement raw tests: material is expected to be a drop-in replacement. This also depends on the tests that have been developed to - Shore A hardness characterize the particular raw material. These tests are - Tensile strength and elongation in the parallel and usually very specific and based on the type, form, and perpendicular-to-roll direction or predominant fiber function of the raw material. direction (//, 3_) - Specific gravity The raw material change is then evaluated in the - Mooney viscosity compounded or mixed AS-NBR material. Analytical - Initial scorch characteristics scale-up of rubber mixing is difficult, so full-scale 500 pound batches at the manufacturer are typically used. Because of their importance in characterizing the Small-scale (6-10 pound) mixing has been used to assist physical properties of the insulation these tests are in down-selecting new raw materials, but is always always run when evaluating raw material changes. followed with full-scale processing. These tests are also conducted on each production lot of AS-NBR; therefore a large production material AS-NBR insulation is mixed using a Banbury® type database is available for comparison. This database is internal mixer. The AS-NBR material is calendered also used to trend the effects of changes following into sheet stock of 0.05, 0.10, 0.13, or 0.20 inch implementation. thickness. Five different extrusions are also made using sheet stock as the feed material. For most evaluation The AS-NBR insulation specification identifies a set of efforts 0.100-inch thick sheet stock is ordered. One qualification tests that are typically conducted to configuration of extrusion may also be ordered if the evaluate all raw material changes. Qualification tests change could affect the ability to extrude the AS-NBR include all of the quality conformance tests listed above material. plus the following: American Institute of Aeronautics and Astronautics A change to the curative agent, accelerator, or activator Raw Material Change Evaluation Methodology is cause to conduct initial scorch and rheology tests. Additional physical properties tests are conducted to Changes to insulation raw materials generally fall under verify that the cross-link density of the cured insulation one of the following categories: has not changed significantly. Insulation erosion testing may also be conducted. 1) A process or ingredient change to the raw material that is not expected to change the properties of the raw Antioxidant changes require aging tests to ensure that material the insulation material is resilient to the effects of 2) An obsolescence issue that causes the raw material oxidation and ozone degradation. Bond tests, including to be replaced with a new raw material that isthe same aging, are required since many antioxidants migrate to chemically and isexpected to be a drop-in equivalent the surface of the material and could affect the bond replacement interface. 3) An obsolescence issue that causes the raw material to be replaced with a new raw material that is Tackifier changes require processing tests to verify that chemically different that may cause the insulation the material has adequate build tack. These tests can material to perform differently. initially be conducted as bench top tests, but are usually followed by a full-scale process simulation article. The category, as defined above, of a specific change will typically influence the number of lots of materials Plasticizer changes are evaluated using comparative ordered to evaluate the change and the number of tests sub-scale and full-scale mix testing. Mix temperatures, conducted. Other factors are considered when mix times, and mechanical loading on the mixer are evaluating raw material changes. The intended function observed. Mechanical properties are also measured to of the raw material being changed dictates which determine the effects of the plasticizer on the cured additional tests (other than the specification insulation. qualification tests) will be conducted to evaluate the change. AS-NBR raw materials fall under one of the following general classifications: Discussion of AS-NBR Raw Material Changes - Elastomer Descriptions of selected changes to RSRM AS-NBR -Filler insulation raw materials are documented in the -Curative agent remainder of this report. The changes that are -Cure accelerator discussed are those that have occurred most recently - Cure activator (since 1987). - Antioxidant - Tackifier - Plasticizer Altax® Accelerator Changes to the elastomer package require physical Altax® (benzothiazyl disulfide), an accelerator used in property tests to verify polymer structure and strength AS-NBR insulation, was manufactured domestically for and to verify that the cross-link density is comparable. 60 years. The original manufacturer decided to Mooney viscosity testing characterizes the flow discontinue production of this and other accelerators. characteristics of the uncured insulation material. The distributor who marketed these products elected to Initial scorch, and rheology tests are conducted to continue to supply the material, but from a new ensure that the elastomer and curative package are manufacturer. The new material used the same Altax® compatible and react at the desired rates and brand name and specification. 1 temperatures. Samples of the old and new Altax® were obtained Changes to the fillers generally require structural along with the supplier's test data for each sample. testing. Viscosity tests are also conducted to ensure Melting point, moisture content, and ash content tests that the material has the desired degree of flow during were repeated at Thiokol. The results indicated that all the cure process. Insulation erosion testing is parameters met specification except melting point. 2 conducted to verify that the thermal and ablative These results were communicated to the supplier who characteristics have not changed. acknowledged the shift in melt temperature and indicated that the Altax® specification would be American Institute of Aeronautics and Astronautics modifietdolistahighemr eltpoint.Thehighmelt Kadox® 930C Zinc Oxide pointwascausebdyaslightlyhighepruritylevel.This wasnotexpectetodhaveanysignificanetffecotnthe Protox®166, an American Process grade zinc oxide, performanocfetheAltax®. was replaced by Kadox® 930C French Process grade zinc oxide. The notification that manufacture of Twosmall-scableatcheosfamodetlesftormulawere Protox®166 had been discontinued was received from mixedusingoldandnewAltax®.Thismodeflormula the zinc oxide manufacturer in October 1989. The zinc wasverysimilatrotheAS-NBRformulae,xcept manufacturer recommended Kadox® 930C zinc oxide additionsaillicawassubstitutefodrtheasbestofibsers. as the replacement for Protox®-166 zinc oxide, stating Thesbeatchewserecompareudsingthefollowingtests: that particle size and treatment levels (surface coating) of both products were essentially the same and that they -ShoreAhardness would perform the same in most applications. Zinc -Tensilestrengtahndelongation oxide is used as a cure activator in the AS-NBR -Specifigcravity formula. Zinc oxide increases the vulcanization rate by -Moonevyiscosity activating the accelerator so that it performs more -Initialscorch effectively. 3 -Rheology -Tearstrength This change was evaluated in conjunction with the change to Agerite Stalite S®. The description of this Nosignificandtifferencewsereobservebdetweethne test effort is included in the "Agerite Stalite S® oldandnewAltax®batchesA.full-scalperoduction Antioxidant" section below. batchwasthenproducebdytheAS-NBRsupplieursing newAltax®.Thefollowingspecificatiotenstswere conducted: Agerite Stalite S® Antioxidant -ShoreAhardness Because of poor sales, the manufacturer of Agerite -Tensilsetrengtahndelongatio(/n/,.1_) White® (Di-beta-naphthyl-paraphenylene diamine), an -Specifigcravity antioxidant, discontinued producing this material. -Specifihceat Agerite Stalite S® (mixture of octylated -Thermaclonductivity diphenylamines) was selected as the replacement -Moonevyiscosity antioxidant. -Initialscorch Three potential replacement antioxidants were initially Thefollowingadditionmalateriaplropertiewserealso identified and tested by the AS-NBR supplier: Anchor tested: DNPD (a chemically identical product), Vanox MTI (chemically different from Agerite White®), and -Tearstrengt(h//,.1-) Agerite Stalite S® (from the same family of amine -Ashcontent antioxidants as Agerite White®). Small-scale mixing -Shrinkage was conducted by the AS-NBR supplier. The following -AS-NBR / liner bond tests tests were conducted on the test batches: -0 & 7 week aging at 77 °F and 150 °F - 180° peel -Shore A hardness - Tensile adhesion - Tensile strength and elongation - Lap shear -Mooney viscosity -AS-NBR/AS-NBR T-peel -Rheology - 180°peel - AS-NBR/metal -Tensile adhesion - AS-NBR/metal Shore A hardness, and tensile strength and elongation - 0,2, 4, 6, weeks aging at 75 °F and 135 °F were repeated on cured material that was aged for 24 -Thermogravametric analysis hours at 158 °F. The data showed no significant differences in these properties between the candidates. No significant differences were observed in AS-NBR Agerite Stalite S® was selected based on its batches mixed with the new Altax® when compared availability, chemical similarity, and the results from with AS-NBR mixed with old Altax®. the test batches. 5 American Institute of Aeronautics and Astronautics This antioxidant change was evaluated in conjunction Agerite Stalite S® antioxidant was the cause of the shift with the change to Kadox® 930C noted in the previous in scorch time. section. 4 Initially three full-scale 500-pound lots of AS-NBR were ordered, two evaluation lots and one Six months following initial receipt and testing of the control lot. The AS-NBR supplier manufactured all first evaluation lots, initial scorch was again tested to these lots during the same mix campaign. The evaluate aging effects of the uncured material. These following tests were conducted on the sheet stock tests showed a typical 1-minute drop in scorch values. material: Rheology was also conducted and produced the same results, minimal reduction in cure initiation values. -Shore A hardness - Aged 2, 4, 7, 14 days, 158 °F The shift in initial scorch time was also reflected in the -Tensile strength and elongation (//, _1_) Ts2 data from the rheology tests. The oscillating disk -Aged 2, 4, 7, 14 days, 158 °F rheometer essentially measures the stiffness of the rubber as the material cures. Ts2 is an indication of the - Specific gravity - Specific heat time required to initiate cure, similar to initial scorch. - Thermal conductivity The shift in scorch time did not affect any of the - Mooney viscosity mechanical or thermal/erosion properties of the cured - Initial scorch NBR. At the beginning of the RSRM insulated - Rheology segment cure cycle, the autoclave is held at 200-230°F - Tear strength (//, .1.) for approximately 2hours. This temperature is below - Witness panel bond tests the curing temperature of the AS-NBR and the step is - Aged 4, 16 weeks, 135 °F designed to provide time for all of the AS-NBR - Seventy-pound charge (SPC) insulation char motors material to reach a constant elevated temperature prior to increasing the autoclave temperature to begin cure. A notable drop in initial scorch time as observed during During this hold period the AS-NBR material has time to flow into the extremities of the mold tooling. the scorch testing of the first two evaluation lots. Initial scorch is an indication of how fast the material will Because of this hold period, the initial scorch begin to cross link (cure) at elevated temperatures. characteristics are less critical from a RSRM processing Two additional lots were made to evaluate the change application standpoint. Additional scorch tests were conducted at 200°F and 230°F for 2 hours to verify that to Agerite Stalite S® and Kadox® 903C. Each of these the material was not curing (at a notable rate) at these two lots was made using a different lot of Kadox® 930C. AS-NBR extrusions were also made from these temperatures. These tests indicated that the material did not cure and would flow at these temperatures. lots to determine if the drop in initial scorch time would affect the ability to extrude the AS-NBR. SPC motor, Initial scorch testing is retained in the AS-NBR _ging, and bond tests were not repeated on these lots. specification because it generally gives an indication of Again a reduction in initial scorch time was observed. the amount of heat history experienced by the material during mixing and processing at the manufacturer. One additional lot of AS-NBR was produced to Two RSRM igniter part cure cycles were modified to evaluate the effects of the Agerite Stalite S® change include the 200-230°F hold step. All RSRM only in an attempt to identify the cause of the shift in components were successfully fabricated following initial scorch. Initially itwas thought that the Kadox® 930C zinc oxide, which functions as a cure activator, implementation of the change to use Agerite Stalite S® was the cause. Testing of this lot of material again and Kadox® 930(2. The following figure illustrates the shift in scorch properties. showed short initial scorch times, indicating that the American Institute of Aeronautics and Astronautics ASNBR-InitialScorch Characteristics -Vendor Data SpecificationLimits5-30minutes 25 1o 5 Production History During this evaluation it was also noted that the Agerite source prior to 1983. No documentation of the previous Stalite S® caused the AS-NBR insulation to have a change from soda ash to caustic soda was found at the lighter color before and after cure. The Agerite Stalite AS-NBR supplier or at Thiokol. S® also eliminated discoloration or darkening of the cured AS-NBR caused by light exposure that had been This change affected the AS-NBR insulation and two silica filled EPDM materials used as external insulation observed prior to this change. materials for the RSRM. A test plan and test report HiSil® 233 Silicon Dioxide were written to evaluate this change to both the SF-EPDM and AS-NBR insulation materials. 5 In November 1992, the AS-NBR supplier was notified of a change in the production of Hi-Sil products The silica manufacturer provided physical and chemical including Hi-Sil 233, silicon dioxide, used in AS-NBR. properties data on the initial silica batches following the The alkali source used in the silica manufacturing alkali change along with historical data for comparison. process was changed from caustic soda to soda ash. This data included surface area, pH, percent weight loss This change was made to reduce the costs to produce at 105°C, and purity (percent SiO2). This data their silica products. confirmed the vendor's statement that the change to the alkali source would not affect the properties of the Hi-Sil 233. Silica products are derived from crystalline sand (SiOz). During the early stages of the process, the crystalline structure of the sand is broken down by converting it to One full-scale batch of AS-NBR was produced using high alkali glass at very high temperature. The alkali the new process Hi-Sil 233. Most of the batch was calendered to 0.100-inch thickness. Three AS-NBR source makes the crystalline sand easier to melt (lowers the melt temperature). The alkali source is strictly a extrusions were also made to determine if the change processing aid in this initial step that facilitates melting had any impact on the ability to extrude the AS-NBR. Both the sheet stock and extrusions were tested for the the sand in the furnace. During subsequent steps in the process, the alkali isconverted to salt and eventually following properties: discarded. The silica manufacturer stated that the end - Shore A hardness silica product would not be changed with a change to the alkali source. The silica manufacturer also - Tensile strength and elongation (//, 1) indicated that soda ash had been used as the alkali - Specific gravity 7 American Institute of Aeronautics and Astronautics -Specifihceat -Thermaclonductivity As part of the initial test effort, Thiokol obtained -Moonevyiscosity samples of both Harwick® F-1500 and Hydrofol® -Initialscorch 1800B stearic acid. The following tests were conducted to compare the two stearic acids: Allofthedatafromthesetestswerewithin specificatiolimnitsandthepreviouhsistoricadlatabase. - Initial and final melting point Nominatel srtesultwserealsoobtainefdromthetests - Ash content performeodntheSF-EPDM. - Acid number - Saponification value Notificatiownasreceiveind1994thatd, ueto - Titre (freezing point) environmenctoanl cerntsh,ealkalsiourcweasbeing - FT-IR analysis changeadgainb,acktocaustiscodaB. ecausoefthe conclusiodnrsawnfromthefirstevaluatiotnh,ischange The data from the above tests indicated that two stearic wasimplementiendtotheAS-NBRmateriawlithout acids were very similar, providing justification to conductinagspecifitcestplan.Thequality proceed with the full-scale batch mixing. The conformandcaetafromthesubsequepnrotductiolonts evaluation of AS-NBR made using Harwick® F-1500 weremonitoretodverifythattheimplementatoiofnthis stearic acid was conducted in conjunction with the changdeidnotaffecAt S-NBRproperties. evaluation of new process Picco® 6100 tackifier, and is discussed inthe following section of this report. In1996thesilicamanufactunreortifiedtheAS-NBR supplietrhataseconsdodiumsilicatefurnacweasbeing constructed. The new furnace would use soda ash as Picco® 6100 Resin Tackifier the alkali source. The original furnace would still use caustic soda. Sodium silicate from both furnaces would During the latter part of 1995, the manufacturer of be blended later in the silica manufacturing process. Picco® 6100 resin restructured their production facility, Again this change was implemented without additional which included shutting down old equipment and testing. The silica manufacturer also indicated that the replacing it with new equipment that was more cost original furnace would eventually be converted to use effective and environmentally compliant. As part of the soda ash. The history of these silica changes indicates restructuring, the resin neutralization process used to that the manufacturer will readily make changes to the make Picco® 6100 was changed from a wet alkali source based on market costs for these chemicals. neutralization process to a dry neutralization process. Fortunately all of the data gathered in conjunction with The manufacturer indicated that the new process changing alkali sources indicate that the alkali source Picco® 6100 resin would meet the previous has no detectable impact on the performance of specification and perform the same as the previous AS-NBR insulation. material. 6 Picco® 6100 resin is included in the AS-NBR Harwick® F-1500 Stearic Acid formulation primarily to provide increased green tack of the uncured material. This is a very important The production facility used to make Hydrofol® 1800B property of NBR in light of the RSRM ply-to-ply stearic acid (originally used in AS-NBR insulation) was insulation build process. It is also a property that is purchased by a company that already had a facility to difficult to measure quantitatively. produce stearic acid. The Hydrofol® 1800B facility was closed. The AS-NBR supplier selected Harwick® Samples of old process and new process Picco® 6100 F-1500 stearic acid as the replacement, based on were obtained and the following tests were conducted specification properties of the two stearic acids. to compare these two materials. Harwick® F 1500 had also been used successfully to replace Hydrofol® 1800B in other insulation materials Specific gravity produced for Thiokol. Ash content - Differential scanning calorimeter (DSC) Stearic acid functions as a cure activator in AS-NBR. - Thermomechanical Analyzer (TMA) During vulcanization, stearic acid and zinc oxide react - FT-IR with the sulfur to increase the rate and efficiency of the cross-linking reaction. American Institute of Aeronautics and Astronautics Allofthesetestsindicatetdhatthenewprocess sulfur manufacturer to prevent dusting and to improve materiawlouldperformsimilatrotheoldprocess dispersion of the sulfur during rubber mixing. Two Picco®6100resinT. hreefull-scaleevaluatiobnatches different sources of oil had been used by the sulfur weremixedtoevaluattehePicco®6100resinchange manufacturer. A new, third oil source was approved for andtheHarwick®F-1500steariaccidchangeT.hese use. The treatment oils used in Crystex® OT 20 sulfur threebatchewsereindividualclyalenderiendto are stored in a single holding'tank. Each order of oil is 0.100-incthhicksheesttocklots.Extrusionwserealso added to the existing supply in the holding tank, producefrdomoneoftheselotsofAS-NBRT.wo resulting in a varying combination of the three oils. additionbaal tchewseremixedo,netoevaluaotenlythe The source selected for each oil purchase is based on newprocesPsicco®6100resinchang(ewith price and availability. Hydrofol®1800Bsteariaccid)a,ndtheothetro evaluatoenlytheHarwick®F-1500chang(ewithold Crystex® OT 20 sulfur is mill-mixed with styrene procesPsicco®6100resin).Thesetwoadditionlaolts butadiene rubber (SBR) by the AS-NBR manufacturer to make asulfur masterbatch. The sulfur / SBR blend werenotfullytestedb,utwereorderesdoifashiftin somepropertwyasobservethdespecificcaus(estearic disperses much more readily in NBR than sulfur alone. acidorPicco®6100resinc)ouldbeidentified. The oil used to treat Crystex® sulfur makes up less than one quarter of one percent of the final AS-NBR TheAS-NBRsuppliearndThiokoclonductethde insulation. Due to the similarity of the various oils qualificatiotenstsonallevaluatiolonts.Thefollowing used, the small amount of oil used, the presence of additionmalateriaplropertietesstswereconducted: other hydrocarbon-derived constituents, and the presence of plasticizer, it was anticipated that the oil -Rheology change would not affect the properties and performance of the AS-NBR insulation. -Tearstrengt(h//,_1_) -AS-NBR/AS-NBTR-peel -AS-NBR One batch of AS-NBR was mixed using "new oil" / case witness panels (witness panels test Crystex® sulfur. A control lot made using the same both tensile and peel bond capability) lots of raw materials (except sulfur) was tested along - AS-NBR / CF-EPDM witness panels side the evaluation lot. Quality conformance tests were - AS-NBR / liner witness panels conducted by the AS-NBR supplier. Thiokol conducted - AS-NBR / carbon cloth phenolic witness panels all of the qualification tests along with rheology and - AS-NBR / glass cloth phenolic witness panels tear strength. Bond tests, including T-peel and - SPC insulation char motors AS-NBR to steel witness panels, were conducted by Thiokol. 7 Bench tests were also conducted to evaluate the tack of the uncured AS-NBR at the Chemlok® 233 The third oil source did not affect properties or vulcanization adhesive to AS-NBR interface and at the performance of the AS-NBR insulation. The sulfur AS-NBR to AS-NBR interface. These tests were manufacturer has recently indicated that an additional conducted using the evaluation lots and production lots oil source will be used in the near future. This new oil of AS-NBR for comparison. Both solvent (TCA) source will require another change evaluation. activated samples and non-activated samples of AS-NBR were roiled against a Chemlok® 233 coated plate and against another sheet of AS-NBR. A fish Sulfur Masterbatch Refining scale was used to measure the peel strength required to remove the samples. Qualitative observations were also In November 1998 hard black spots were observed on made of the tack tests. the visible surfaces of the cured AS-NBR insulation in RSRM segments. A limited number of black hard spots The above noted tests verified that AS-NBR made are allowed in the insulated segment finalization using Harwick® F-1500 stearic acid and new process inspection specification, but these segments had notably Picco® 6100 resin would perform the same as previous more than the specification allows. Analysis of AS-NBR material. extracted samples of these spots indicated that they were sulfur rich. Some of the hard spots had a yellow, pure sulfur center. Samples from the lots of the sulfur Sulfur Oil masterbatches used to make these AS-NBR lots revealed small hard Crystex® OT 20 clumps that had Crystex® OT 20 sulfur is used as the curative in been compressed into small hard particles. These sulfur AS-NBR insulation. Oil is added to the sulfur by the American Institute of Aeronautics and Astronautics