How to Control Porosity in Extruded EPDM Dense Pro Le

14 Rubber & Plastics News • March 22, 2021 www.rubbernews.com www.rubbernews.com Technical Technical

volatiles can vaporize. Once this filler surface moisture evapo- rates it allows more filler inter- How to control porosity in action with other ingredients such as PEG and other process aids. Desiccants like CaO are added late in the mixing cycle to extruded EPDM dense pro le prevent absorption of moisture. A two-roll mill below the mixer By Greg Li, Santosh Bawiskar The authors further can be used to complete the and Sharon Wu Executive summary mixing, optimize dispersion and let Dow Packaging & Specialty Plastics Greg Li is a research scien- volatiles escape by creating and re- Introduction The fully saturated hydrocarbon backbone of EPDM rubber results in outstanding weatherability, tist in North newing the surface. The roll speed EPDM dense profile and manu- ultraviolet stability and low/high temperature resistance. Therefore, EPDM rubber has been estab- America Pack- is adjusted so air is not trapped in facturing process lished as the primary polymer choice for automotive sealing applications (both dense and sponge aging & Spe- the compound, as this can result in The fully saturated hydrocar- weatherstrip). cialty Plastics porosity as well. Finishing ingredi- bon nature of EPDM rubbers re- A typical manufacturing process of automotive dense weatherstrip involves profile extrusion fol- Technical Ser- ents like slab dips must be appro- sults in outstanding weather- lowed by continuous vulcanization. Excessive porosity in extruded and fully cured dense profiles re- vice & Develop- priately selected as these can be ability, ultraviolet stability and mains a big challenge to many automotive weatherstrip tier suppliers. ment at Dow sources of volatiles. low/high temperature resistance. In this study, we systematically studied the mechanism of porosity formation in EPDM dense pro- Chemical Co. Therefore, EPDM rubber has file. The major factors for porosity in EPDM dense profile were summarized as compound formulation; His responsibil- Extrusion been established as the primary extrusion conditions; and vulcanization conditions. ities include the Li The extrusion step also can be polymer choice for automotive A porosity-free technical solution for EPDM dense profile also was presented. development used to control porosity. As the sealing applications. of Nordel-brand EPDM prod- compound is being conveyed ucts, formulations and applica- through the extruder, it imparts TECHNICAL NOTEBOOK • It reduces mechanical prop- ation and bubble growth has to result in porosity. tion and processing develop- additional mixing due to the mo- Edited by John Dick erties such as tensile, tear, ad- be mitigated by controlling the Calcium oxide can help bind ments. tion of the screw and the type of hesion, etc.; volatiles/air entrapment, or by the moisture by functioning as a Santosh Bawiskar is a fellow screw design. With a two-stage Automotive body sealing (both • It changes performance char- applying external pressure on desiccant. Further oils get ab- at Dow. He has more than 20 screw, with a devolatilization sec- dense and sponge weatherstrip) acteristics (e.g. sealing) as the the extrudate. sorbed on porous filler surfaces, years of experi- tion, it is possible to pull vacuum, represents one of the largest ap- stiffness and density are reduced which may or may not incorpo- ence in materi- which allows extraction of the vola- plications, accounting for about (in cases of high porosity); and Variables affecting porosity rate into the EPDM matrix and al development, tiles. The back pressure due to the 20 percent of the total worldwide • Customer specifications don’t The compound design (formu- can act as a source of volatiles. compounding die allows volatiles to escape from 1,2 consumption of EPDM. allow porosity even if perfor- lation) and the subsequent man- Low molecular weight oils also and processing the vent and proper screens/die A typical manufacturing pro- mance is unaffected. ufacturing steps can impact po- are more volatile and a source of of elastomers. design can be used to adjust this. cess of automotive dense weather- The mechanism of porosity or rosity of the cured profile parts. porosity. Many low molecular B a w i s k a r Generally, higher extrusion strip includes the following steps: bubble formation involves bubble The manufacture of an extruded weight ingredients like process graduated with temperatures and screw speeds • Compound formulating and nucleation followed by bubble dense profile broadly involves three aids and curatives at low concen- a doctorate in help devolatilization, although mixing; growth. During extrusion, nucle- steps: compound mixing; extrusion trations can have high volatility, polymer engi- Bawiskar there is an upper limit for the • Profile extrusion; and ation occurs when the rubber and shaping; and curing. which can cause porosity. neering from extrudate temperature consider- • Curing. material is supersaturated with Each of these steps can con- Purity of these ingredients also the University of Akron and an ing the possibility of scorch. A volatile materials and the vapor tribute to the formation of poros- is critical. Volatiles also can result MBA from Clarion University. good screw design will avoid Porosity in dense EPDM profile pressure of the volatiles exceeds ity in an extruded part. Con- from byproducts of the curing re- He serves on the Board of the dead spots, ensure mixing and Porosity is the unintentional the external pressure on the ex- versely, optimizing these steps action. For example, peroxide de- TPE Special Interest Group of surface renewal, allow a depres- formation of bubbles or voids in trudate. This is followed by diffu- can help prevent porosity. composition can result in volatiles the Society of Plastics Engineers. surized zone in a two-stage screw an extruded or molded dense sion of the volatile materials to like acetone being formed. Sharon Wu is a product develop- and result in adequate tempera- part. In the case of sponge or the nuclei, which results in bub- Compound design Besides the compound formula- ment leader who oversees the ture buildup. foamed parts, the bubbles or cells ble growth. An EPDM formulation consists tion, the choice of EPDM rubber Nordel EPDM product and In the case of hot feed extru- are intentionally created by us- Although porosity formation is of fillers, oils, process aids, cure also is critical. Typically, EPDM technology innovation pipeline, sion, the additional warming ing physical or chemical blowing mostly due to volatiles as trapped package and other ingredients. with low volatile organic compound and leads a global team to de- step on a two-roll mill also can agents. In the case of dense ex- air during mixing, milling or ex- Many of these ingredients are (VOC) and high Mooney viscosity is velop next-generation EPDM help reduce volatiles and mois- truded parts (for example weath- trusion also can cause this. polar and not easily wetted by preferred for compound design to with new, valu- ture, which may have been ab- erstripping, hose, profiles, etc.) Therefore, in order to control the non-polar EPDM. If not fully incorporate all the ingredients and able properties. sorbed during storage. the porosity is undesired because: porosity formation during dense wetted, the filler surface can act enable the compound to resist any Her career • It is difficult to control di- profile manufacturing process, as heterogeneous nucleation bubble formation and growth. Due with Dow be- Curing mensions of a porous part; the mechanism of bubble nucle- sites. This is especially true with to the inherent feature of Nor- gan in 2008, As the material exits the die, non-black fillers, which tend to del-brand EPDM manufacturing and she has led the external pressure drops to Table 1: List of dense compound formulations. be more polar. process, low VOC Nordel EPDM is multifunction- atmospheric levels and bubble Use of process aids like poly- a favorable polymer choice for an al global teams nucleation and growth may oc- ethylene glycol (PEG) helps filler EPDM-dense compound. toward the cur. This is especially true with wetting. Another issue with commercial- Wu lower viscosity or lower melt many non-black fillers (clay, etc.) Mixing ization of a se- strength feedstocks, which do is that they inherently have a Mixing is a critical step to en- ries of polyolefin elastomers for not resist bubble nucleation. high moisture content, which can sure good dispersion of all ingre- the transportation, infrastruc- Lowering extrudate temperature and packaging markets. Table 2: One-pass mixing procedures. ture can help if bubble formation She received her doctorate from occurs instantly after exiting the the Georgia Institute of Technolo- die. Curing also helps build com- gy, and her research has covered pound viscosity and prevent po- many aspects of polyolefin mate- rosity. Thus, the kinetics of bub- rials science, including structure/ ble formation must be slower property relationship, prod- than the kinetics of curing in or- uct-process development and der to prevent porosity. polyolefin characterization. The cure rate and cure set-up Wu’s research has resulted (hot air, microwave, salt bath, in 16 peer-reviewed journal autoclave, etc.) play a significant articles, 15 granted U.S. pat- role in controlling porosity. The ents and more than 26 patent autoclave process is most forgiv- applications. ing for porosity as external steam pressure can be applied to dients and can be used to elim- prevent porosity development. inate volatiles like moisture In the hot air cure and salt bath coming from fillers and other process, curing starts from the ingredients. Good dispersion surface and progresses inward, ensures that the filler surface allowing time for porosity develop- is not a source for heteroge- ment. In microwave curing, cure neous nucleation. Good mixing rate is more uniform throughout also ensures that the oil is well the cross-section, and using a incorporated into the EPDM shock oven can help form a skin phase rather than remaining layer quickly. In some cases, exter- absorbed on the filler surface. nal pressure can be applied even Further, as the compound during continuous curing. temperature is elevated during In this paper we critically exam- mixing, moisture and other ine some of the variables affecting

P014_P017_RPN_20210322.indd 14 3/17/21 5:35 PM www.rubbernews.com www.rubbernews.com Rubber & Plastics News • March 22, 2021 15 Technical Technical

volatiles can vaporize. Once this porosity and provide guidelines for gies Mooney viscometer following with a dilute solution of silicone. section. Tensile properties (tensile filler surface moisture evapo- manufacturing porosity-free ex- ASTM D1646. The measurement The samples were in a preheated strength and elongation) were rates it allows more filler inter- truded dense profiles using micro- conditions were 100oC for com- mold, taking care to place prop- measured at room temperature, action with other ingredients wave/hot air curing oven. pounds using large rotors at ML erly for mill direction. The plat- following the method ASTM D412. such as PEG and other process (1’ + 4’) conditions with a rotor ens were closed. The “normal” aids. Desiccants like CaO are Materials and experiments speed of 2 RPM. operating pressure was 100 tons, Shore A hardness properties added late in the mixing cycle to Formulations for EPDM dense or as shown on the gauge as Shore A hardness properties prevent absorption of moisture. compounds MDR 200,000 pounds. were measured using stacked A two-roll mill below the mixer There are a total of six different Compound cure kinetic profiles When cure time ended, the bot- three die-cut specimens. Three The authors further can be used to complete the formulations used in this study at 180oC were measured using a tom platen automatically opened. die-cut specimens were cut from mixing, optimize dispersion and let (Table 1). The compound formu- rotorless cure rheometer (MDR— The samples were removed, and the compression molded plaques, Greg Li is a research scien- volatiles escape by creating and re- lations were adjusted to achieve moving die rheometer, Alpha immediately placed in water to which were prepared as de- tist in North newing the surface. The roll speed different compound hardness Technologies MDR 2000) as spec- stop the curing. Samples were scribed under the compression America Pack- is adjusted so air is not trapped in targets, i.e. 60 Shore A, 70 Shore ified in standard test method conditioned for 24 hours at room molding section. Shore A hard- aging & Spe- the compound, as this can result in A and 80 Shore A, respectively. ASTM D5289. The test tempera- temperature prior to testing. ness properties were measured cialty Plastics porosity as well. Finishing ingredi- Also, two different cure packages ture was set at 180oC with a 0.5° To vulcanize the samples, the at room temperature, following Technical Ser- ents like slab dips must be appro- were employed in this study to arc. Maximum (S’, MH) and min- samples were under minimum the method ASTM D2240. vice & Develop- priately selected as these can be investigate the effect of a nitrosa- imum (S’, ML) torque values were compression pressure of 3.5 Mpa ment at Dow sources of volatiles. mine-free cure package on the fi- recorded for each sample. (500 psi) at 180°C using t95 data Physical properties after heat aging Chemical Co. nal compound properties. The time to reach 90 percent of plus 3 minutes for plaques and For heat-aged tensile proper- His responsibil- Extrusion maximum torque (t90) was re- using t95 data plus 15 minutes ties measurement, the test speci- ities include the Li The extrusion step also can be Compound mixing procedures corded and used for the curing of for compression set buttons. mens were first die-cut from the development used to control porosity. As the All of the compound mixing molded test plaques. cured plaque, as described above, of Nordel-brand EPDM prod- compound is being conveyed was carried out on an industrial Vulcanizates physical using the “dumbbell”-shaped ucts, formulations and applica- through the extruder, it imparts scale rubber internal mixer with Compression molded plaques properties tensile die. Those fabricated test tion and processing develop- additional mixing due to the mo- 135L net volume and intermesh- The physical properties of the Original tensile stress-strain specimens were then aged in an ments. tion of the screw and the type of ing rotor design and hydraulic formulations were measured from properties air ventilated oven at 70oC, at Santosh Bawiskar is a fellow screw design. With a two-stage ram control system. vulcanized sheets, cured in a com- Tensile properties were mea- the desired aging hours. at Dow. He has more than 20 screw, with a devolatilization sec- The following mixer settings pression molder (for tensile, com- sured using specimens that were The heat-aged physical proper- years of experi- tion, it is possible to pull vacuum, were utilized for one-pass mixing pression set testing, temperature die cut, using a “dumbbell”-shaped ties were then measured using ence in materi- which allows extraction of the vola- of the proposed formulations: retraction). Samples from the un- tensile die, having the dimensions those heat-aged test specimens. al development, tiles. The back pressure due to the • Fill factor = 0.74 for 60 Shore cured blankets were cut, heated described in ASTM D412. Three Tensile properties (tensile strength compounding die allows volatiles to escape from A compound formulation; and cured in a compression molder die-cut specimens were cut from and elongation at break) were and processing the vent and proper screens/die • Fill factor = 0.72 for 70 Shore to make test specimens in accor- the compression molded plaques, measured at room temperature, of elastomers. design can be used to adjust this. A compound formulation; and dance with ASTM D3182, using a which were prepared as described following the method ASTM D412. B a w i s k a r Generally, higher extrusion • Fill factor = 0.70 for 80 Shore PHI (100 ton press). under the compression molding See EPDM, page 16 graduated with temperatures and screw speeds A compound formulation. The desired mold (6 in. x 6 in., a doctorate in help devolatilization, although The detailed mixing procedures/ or compression buttons) was Table 4: List of dense compound formulations. polymer engi- Bawiskar there is an upper limit for the steps are illustrated in the Table 2. placed on a platen. The sample neering from extrudate temperature consider- (uncured blanket) was cut slight- the University of Akron and an ing the possibility of scorch. A Uncured compound testing ly smaller than the dimensions of MBA from Clarion University. good screw design will avoid Mooney viscosity the individual mold cavity. The He serves on the Board of the dead spots, ensure mixing and Mooney viscosity of mixed mill direction was marked and TPE Special Interest Group of surface renewal, allow a depres- EPDM compounds were mea- the sample was labeled. the Society of Plastics Engineers. surized zone in a two-stage screw sured using an Alpha Technolo- The mold was spray brushed Sharon Wu is a product develop- and result in adequate tempera- Fig. 1: An Omega testing profile die utilized for extrusion. ment leader who oversees the ture buildup. Nordel EPDM product and In the case of hot feed extru- technology innovation pipeline, sion, the additional warming and leads a global team to de- step on a two-roll mill also can velop next-generation EPDM help reduce volatiles and mois- with new, valu- ture, which may have been ab- able properties. sorbed during storage. Her career with Dow be- Curing gan in 2008, As the material exits the die, and she has led the external pressure drops to Table 5: Original and heat-aged physical properties of EPDM compounds. multifunction- atmospheric levels and bubble al global teams nucleation and growth may oc- toward the cur. This is especially true with commercial- Wu lower viscosity or lower melt ization of a se- strength feedstocks, which do ries of polyolefin elastomers for not resist bubble nucleation. Table 3: Extrusion conditions. the transportation, infrastruc- Lowering extrudate temperature and packaging markets. ture can help if bubble formation She received her doctorate from occurs instantly after exiting the the Georgia Institute of Technolo- die. Curing also helps build com- gy, and her research has covered pound viscosity and prevent po- many aspects of polyolefin mate- rosity. Thus, the kinetics of bub- rials science, including structure/ ble formation must be slower property relationship, prod- than the kinetics of curing in or- uct-process development and der to prevent porosity. polyolefin characterization. The cure rate and cure set-up Wu’s research has resulted (hot air, microwave, salt bath, in 16 peer-reviewed journal autoclave, etc.) play a significant articles, 15 granted U.S. pat- role in controlling porosity. The ents and more than 26 patent autoclave process is most forgiv- applications. ing for porosity as external Fig. 2: One-pass mixing curves. steam pressure can be applied to dients and can be used to elim- prevent porosity development. inate volatiles like moisture In the hot air cure and salt bath coming from fillers and other process, curing starts from the ingredients. Good dispersion surface and progresses inward, ensures that the filler surface allowing time for porosity develop- is not a source for heteroge- ment. In microwave curing, cure neous nucleation. Good mixing rate is more uniform throughout also ensures that the oil is well the cross-section, and using a incorporated into the EPDM shock oven can help form a skin phase rather than remaining layer quickly. In some cases, exter- absorbed on the filler surface. nal pressure can be applied even Further, as the compound during continuous curing. temperature is elevated during In this paper we critically exam- mixing, moisture and other ine some of the variables affecting

P014_P017_RPN_20210322.indd 15 3/17/21 5:36 PM 16 Rubber & Plastics News • March 22, 2021 www.rubbernews.com www.rubbernews.com Technical BKT budgets $257 million for plant expansions Tire Business tion (CV) line that had a combi- control and fast mixing cycles (<3 was designed for EPDM com- resistance; nation of multiple hot air ovens minutes) were achieved with the pounds to enable fast extrusion • Mechanical strength, includ- MAHARASHTRA, India—The board of di- and microwave ovens. proposed formulations and mixing and curing speed during the ing tensile and tear; and rectors of Balkrishna Industries Ltd. EPDM (BKT) has approved a capital investment In this study, the CV line con- procedures. Good mixing power vulcanization process. The com- • Long-term sealing capability Continued from page 15 sisted of a total of three 20-foot (250 kW) also was achieved, en- pound target cure speed, (i.e. ts2 and durability. plan valued at $257 million to increase Tensile test was conducted not ovens. The first and third ovens abling good filler dispersion. at 180°C) was approximately 0.7 The original and heat-aged capacity at plants in India, including its less than 16 hours nor more than are hot air ovens with adjustable As the compound hardness in- minutes. Due to the higher filler physical properties of all the large OTR factory in Bhuj and a new fac- 96 hours after specimens being belt speed, hot air temperature creases, the filler and oil incorpo- loading and less oil extension, cured EPDM compounds are tory being built in Waluj. removed from the hot oven. and air velocity. The second oven ration rates slow down. The ram the higher hardness compound is listed in Table 5. The board of directors also disclosed in a is a 20-foot microwave oven with did not reach the fully seated po- having higher compound Mooney In order to control the compound published document their intention to Dense profile extrusion and three adjustable microwave mag- sition until the later stage of the than the softer compound. hardness, a blending of semi-crys- “shelve” plans for a U.S. plant, which has vulcanization process netrons (max power 6kW in total, mixing process. Therefore, spe- OEMs set specifications and talline EPDM grade; adjusted fill- been under consideration since late 2018. All six dense compounds were 2kW for each zone) as well as ad- cial care was needed to optimize categorize the dense profiles by er loading; and adjusted oil content Those plans were suspended nine months extruded on a 3.5-inch sin- justable belt speed, hot air tem- the mixing process for the 80 the hardness group based on the were adopted in the formulation later, in August 2019, due to “business un- gle-screw rubber cold feed ex- perature and air velocity. Shore A compound with higher different needs for sealing of the optimization. certainties” related to difficult macroeco- truder with a 10:1 L/D ratio amount of filler and less oil. car body. There are several criti- The 80 Shore A compound has nomics and volatile climate conditions. screw design with a hollow Ome- Results and discussion cal property requirements that 50 phr of semi-crystalline EPDM ga shape die design (i.e. profile Mixing Compound properties need to be met, such as: grade (Nordel 4770), higher car- shape as shown in Fig. 1.) Mixing curves for all the differ- Uncured compound Mooney vis- • A defect/gel free smooth sur- bon black loading level and less Technical The extruded profile was con- ent hardness compounds are in- cosity and curing characteristics face; oil content. As the compound tinuously cured on a vulcaniza- cluded in Fig. 2. Good temperature Nordel-brand 6565 XFC grade • Excellent compression set hardness increases, the compound tensile strength increases Table 6: Samples with different formulations adjusted for hardness. Table 7: Samples with different curing conditions. as well. As the compound hard- EPDM ness increases, the compound Continued from page 16 compression set increases and tion for porosity. TR 10 increases as well. The cross-sections of those profiles are shown in Fig. 3. It is Porosity study of cured very noticeable that there are Fig. 3: Porosity of EPDM compounds with different hardnesss. Fig. 4: Porosity of EPDM compounds with different curing conditions. profile after extrusion and differences in terms of porosity vulcanization process among those samples. Effect of compound formulation Sample 1, with the lowest (compound hardness) on porosity compound hardness, had the In the first set of experiments, most porosity. Sample 3, with three different compounds were the highest compound hardness, extruded and cured at the same had the least amount of porosity. conditions (Table 6). The cured It is believed there were some profiles were collected at the exit volatiles generated inside the of the microwave curing oven and EPDM rubber compound during examined the profile cross-sec- the curing process, and the high See EPDM, page 17 compound viscosity would sup- press the bubble nucleation and bubble growth. Therefore, as the compound hardness (compound Mooney viscosity) increased, the bubble nucleation and growth were suppressed, and therefore

Table 8: Samples with different cure packages.

Fig. 5: Porosity of EPDM compounds with different cure packages.

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P014_P017_RPN_20210322.indd 16 3/17/21 5:36 PM www.rubbernews.com www.rubbernews.com Rubber & Plastics News • March 22, 2021 17 BKT budgets $257 million for plant expansions Tire Business resistance; The document’s use of the term “shelve” ment. Overall capacity would be expanded • Mechanical strength, includ- MAHARASHTRA, India—The board of di- leaves open the potential for the project to by 50,000 metric tons per year. ing tensile and tear; and rectors of Balkrishna Industries Ltd. be revived at some point, but for now the • $88 million to complete work on a car- • Long-term sealing capability (BKT) has approved a capital investment company said it is focusing on a strategy to bon black processing plant at the Bhuj factory and durability. plan valued at $257 million to increase “increase (its) share of business in U.S. complex and expand its capacity nearly 75 The original and heat-aged capacity at plants in India, including its markets by increasing supplies from India.” percent to 200,000 metric tons per year; and physical properties of all the large OTR factory in Bhuj and a new fac- The U.S. represents 15 percent of BKT’s • $60 million to carry out moderniza- cured EPDM compounds are tory being built in Waluj. global sales, according to the firm’s third tion, automation and technology upgrades listed in Table 5. The board of directors also disclosed in a quarter financial report. This equates to at the Bhuj and Rahasthan factories. In order to control the compound published document their intention to about $130 million on an annualized basis. In addition, BKT said work progresses on hardness, a blending of semi-crys- “shelve” plans for a U.S. plant, which has The newly approved investment pack- a farm/industrial/OTR tire plant being built talline EPDM grade; adjusted fill- been under consideration since late 2018. age calls for: in Waluj, Maharashtra, that will replace a er loading; and adjusted oil content Those plans were suspended nine months • $108 million to boost output of 51- 30-year-old facility nearby. BKT said it ex- were adopted in the formulation later, in August 2019, due to “business un- and 57-inch OTR tires at the factory in pects the new plant to be operational by the optimization. certainties” related to difficult macroeco- Bhuj, along with debottlenecking and the first quarter of 2022 with a start-up capacity BKT plans to invest $257 million to expand its The 80 Shore A compound has nomics and volatile climate conditions. installation of additional ancillary equip- of 30,000 metric tons per year. plants in Bhuj and Waluj, India. 50 phr of semi-crystalline EPDM grade (Nordel 4770), higher car- bon black loading level and less Technical oil content. As the compound there was less porosity caused by tion and a very smooth profile ventional cured profiles. Sample 9 curing time shorter, therefore re- hardness increases, the com- the volatiles in the high hardness surface as well. and Sample 10 are completely po- ducing the amount of any low boil- pound tensile strength increases EPDM and high Mooney compound It is believed that the excessive rosity-free structures. ing temperature nitrosamine gen- as well. As the compound hard- during heating and curing. heat (generated by the high-pow- It is believed that the by-prod- erated. It is believed the low boiling ness increases, the compound Continued from page 16 er microwave) generated more ucts produced by nitrosamine-free temperature nitrosamine causes compression set increases and tion for porosity. Effect of curing conditions (oven volatiles and reduced the com- accelerators have higher boiling the bubble nucleation and growth, TR 10 increases as well. The cross-sections of those temperature and microwave pow- pound viscosity. This also could temperatures. Therefore, the vol- and resulting in the porosity in the profiles are shown in Fig. 3. It is er) on porosity potentially limit the bubble atiles during curing were much cured compound. However, a faster Porosity study of cured very noticeable that there are In the second set of the study, growth and therefore increase less and no bubble nucleation and extrusion speed is not always fa- profile after extrusion and differences in terms of porosity the same compound formulation the porosity inside the compound. growth were formed by the nitro- vorable since it could potentially vulcanization process among those samples. -3 was extruded but cured at dif- On the other hand, lesser micro- samine-free cure system. cause under-cured products. Effect of compound formulation Sample 1, with the lowest ferent conditions (different mi- wave power wouldn’t raise the On the other hand, the tradi- (compound hardness) on porosity compound hardness, had the crowave power levels) (Table 7). profile temperature too high, tional sulfur-cure accelerators (i.e. Conclusions In the first set of experiments, most porosity. Sample 3, with The cured profiles were collected which prevents any volatile for- dithiocarbamates, sulfenamides, Excessive porosity in extruded three different compounds were the highest compound hardness, at the exit of the microwave cur- mation and therefore reduces the thiurams and some sulfur donor) and fully cured EPDM dense extruded and cured at the same had the least amount of porosity. ing oven and examined the pro- porosity inside the compound. tend to release lots of low boiling profiles remains a big challenge conditions (Table 6). The cured It is believed there were some file cross-section for porosity. temperature nitrosamines, which to many automotive weatherstrip profiles were collected at the exit volatiles generated inside the The cross-sections of those pro- Effect of curative package-type of caused the porosity the during the tier suppliers. of the microwave curing oven and EPDM rubber compound during files are shown in Fig. 4. accelerators on porosity extrusion and curing process.3 In this study, we systematical- examined the profile cross-sec- the curing process, and the high Sample 4, with highest micro- In the third set of the study, ly studied the mechanism of po- See EPDM, page 17 compound viscosity would sup- wave power setting, exhibited the difference between the cura- Effect of extrusion speed on porosity rosity formation in EPDM dense press the bubble nucleation and the most porosity and very rough tive packages were investigated. Another study was conducted profiles. It is believed the porosi- bubble growth. Therefore, as the profile surface among all the Conventional sulfur-cure sys- to extrude the same compound ty formation in EPDM-dense compound hardness (compound samples. On the other hand, tems (Samples 1-3) were com- formulation (i.e. -2) at two differ- profiles were caused by the low Mooney viscosity) increased, the Sample 7, with the lowest micro- pared with the nitrosamine-free ent speeds, and therefore cured boiling temperature nitrosamine bubble nucleation and growth wave power setting, exhibited an cure system (Samples 8-10). with different dwell times. The produced by rubber accelerators were suppressed, and therefore almost porosity-free cross-sec- The extrusion and curing con- samples and cross-sections are during the curing process. ditions for those compounds are shown in Table 9 and Fig. 6. Practical approaches to reduce Table 8: Samples with different cure packages. listed in Table 8. The cross-sec- It was observed that the higher the amount of nitrosamine vola- tions of those profiles are shown extrusion speed and shorter curing tiles during curing are very ef- in Fig. 5. time reduced the porosity in the fective to control the porosity in Even though the microwave compound. It is believed that the the cured compound. Therefore, power setting was higher for the higher extrusion speed will have it is highly recommended that compounds with the nitrosa- higher head pressure, therefore lower oven temperature; lower Fig. 5: Porosity of EPDM compounds with different cure packages. mine-free cure package (samples helping to get rid of any trapped air microwave power setting; short- 8-10), the profiles with the nitro- in the compound after extrusion. er curing time; and choice of ni- samine-free cure package showed Most importantly, the faster ex- trosamine-free accelerators are much less porosity than the con- trusion speed will make the rubber very effective to control the porosity in the dense compound. Table 9: Samples with different extrusion speeds. In addition, higher compound viscosity or higher compound June 1-3, 2021 • Virtual Edition hardness are beneficial to prevent bubble growth and porosity.

References 1. Li, G.; Li Pi Shan, C.; Wickham, R.; Featured Speaker Fig. 6: Porosity of EPDM compounds with different extrusion speeds. Nguyen, L.; Han, T.; and Laakso, R.; EPDM Product, Formulation and Process for Making Automotive Sponge Weather- strip, ACS Rubber Division 192nd Techni- cal Meeting, Paper #C27, Cleveland (2017). 2. Li, G.; Bawiskar, S.; Wickham, R.; Yang, W.; EPDM Formulation Develop- ment and Optimization for Dense Profile Application, ACS Rubber Division 193rd Bill Hyde Technical Meeting, Paper #26, Indianap- olis (2018). Our Sponsors 3. Bryan G. Willoughby; Keith W. Scott, Executive Director, Oleﬁns & Elastomers Nitrosamine Formation in Rubber II: Influence of Cure, Rubber Chemistry & IHS Markit Technology, (1998), 71(4): 766-777. Trends in Rubber and Feedstock Markets and the E ect on Automotive Independent Testing and Development for Oil and Gas Applications for Over 55 Years

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