Grantee Research Project Results

Final Report: Reduction or Replacement of 6PPD through Improved Ozonation-related Crack Resistance with MOLECULAR REBAR

EPA Contract Number: 68HERC24C0030
Title: Reduction or Replacement of 6PPD through Improved Ozonation-related Crack Resistance with MOLECULAR REBAR
Investigators: Swogger, Kurt
Small Business: Molecular Rebar Design, LLC
EPA Contact: Richards, April
Phase: I
Project Period: December 1, 2023 through May 30, 2024
Project Amount: $99,989
RFA: Small Business Innovation Research (SBIR) - Phase I (2024) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR)

Description:

Molecular Rebar Design, LLC (MRD) used a solutions-based approach to determine a multi-component composition to replacement of antiozonant 6PPD in tires. Enabling the removal of 6PPD from tires reduces tire-associated environmental contaminants causing damage to aquatic ecosystems, such as 6PPD-quinone causing salmonid deaths. MRD performed 5 tire rubber compound studies with over 35 individual formulations to select an optimum type and loading of the MOLECULAR REBAR® (MR) carbon nanotubes and to determine required modifications to the tire compound formulation to enable the removal of 6PPD. The MR carbon nanotubes have greatly improved impact on mechanical and physical properties and greatly reduced effects on animals, their tissues, cells, and chromosomes compared to normal as-made carbon nanotubes. Numerous tests relating to ozone resistance, characterization of rubber toughness both pre-/post-ozone, and general physical property measurements were conducted by MRD and its subcontractors in Ohio, ACE Laboratories and Akron Rubber Development Laboratory, to demonstrate technical feasibility for this combination of technologies to negate the need for 6PPD/PDs in tire rubber formulations. This was accomplished on time and within budget in six months, from December of 2023 to May of 2024.

Summary/Accomplishments (Outputs/Outcomes):

This project’s outcomes demonstrate that the use of MR reinforcing carbon nanotubes, in combination with antioxidants and protective agents that are classified as being safer for health and the environment than 6PPD/PPDs, can produce elastomeric tire compounds that have equivalent ozone resistance, and improved physical properties, as compared to incumbent, state-of-the-art, tire compounds utilizing 6PPD. The combination of technologies, namely the Molecular Rebar and additional loadings of polymerized 2,2,4-Trimethyl-1,2-Dihydroquinoline (TMQ- an antioxidant) and protective waxes, is very feasible for use given the commercial nature of all three constituents. MR is used commercially in rubber parts/goods, with ongoing commercialization efforts in various tire tread applications, while TMQ and waxes are used routinely at great scale in the rubber/tire industry. The use of these technologies to remove 6PPD entirely from the rubber compounds in tires would provide a rapidly-implementable solution to the environmental concerns regarding fish kill from 6PPD.

Conclusions:

In this project, MRD demonstrated that the use of MR with loadings of TMQ and protective waxes and no 6PPD perform the same, or better, than typical tire sidewall compounds with 6PPD & carbon black reinforcement based on standard tests specified by the rubber industry. Replacing a portion of the existing carbon black with a smaller quantity of the highly reinforcing MR, coupled with replacement of 6PPD with additional loadings of TMQ (polymerized 2,2,4-Trimethyl-1,2-Dihydroquinoline- an antioxidant) and petroleum waxes- microcrystalline & paraffinic, results in a tire compound with the same, or better characteristics, including ozone resistance, as a state-of-the-art compound using carbon black and 6PPD.

Evidence of improved reinforcement with the Molecular Rebar includes improved modulus, DIN abrasion resistance, improved rolling resistance, and improved intrinsic strength characteristics. The combination of Molecular Rebar and common antioxidants to replace 6PPD were demonstrated to have similar anti-ozone degradation characteristics, with supporting evidence being the Pass rating on ASTM D1149 B, B1, better Mini-DeMattia lifetime post-ozone aging than the control, and reduced number of crack formations post-ozone as measured by optical microscopy.

The use of these three compound ingredients (MR, TMQ, wax) have reduced detrimental environmental effects as compared to 6PPD/its derivatives. In this study, MRD demonstrated that the use of the carbon nanotubes themselves do not increase the dissolution of 6PPD into the environment. Previous research by MRD indicates that although Molecular Rebar are nanoparticles, it is not of high concern for the environment- the nanotubes remain embedded in the shed rubber particles, multiple in vitro studies demonstrate biocompatibility of the MR (discrete multi-wall carbo nanotubes), and it is expected that CNTs that do end up in the environment are oxidized and decomposed when exposed to UV light.

TMQ is classified by the State of Washington as BM-2 (Use but Search for Safer Substitutes), a level safer than most PPDs/PDs, while the waxes used (petroleum- paraffin & microcrystalline) are non-toxic and non-carcinogenic and are often even used for food-safe polymer components.

The combination of Molecular Rebar with typical antioxidants, TMQ and protective waxes, is a readily-implementable solution to removal of 6PPD from tire sidewall and tread compounds, creating rubber compounds for tires that are of lower concern for human health and the environment without sacrificing tire safety and performance.

MRD personnel participated in the George Washington University I-corps program. The skills & thought processes taught during the course seem valuable in verifying the market need, value, and future commercialization of any products developed during the course of this EPA award. Multiple customer and customer-adjacent research interviews have been conducted as a part of this course, one of which has resulted in MRD being added to the Washington State 6PPD Action Plan advisory committee. Valuable insights were gleaned from these meetings over a few months regarding the state’s proposed path forward, it & its stakeholders’ opinions on potential replacements for 6PPD, and expectations on timelines for potential 6PPD ban(s) and implementation of solutions.

MRD and Foresight (TABA vendor) finalized the report focusing on “Expert and End-User Identification; Identification of Potential Partners; Commercialization Plan Advisory” for this project. MRD plans to follow through with much of the advice regarding commercialization plan advisory for a Phase II application, and has already had some meetings with potential partners, supporters, and providers of services (testing/analysis) for future experimentation and commercialization. Multiple tire manufacturers and specialty chemical (antiozonant/antioxidant) manufacturers are interested in the outcome of this project and the potential for collaboration under a Phase II award. Other stakeholders that can influence commercialization have been supportive of MRD’s work, including rule-making bodies.

MRD intends to collaborate with all parties in the value chain, in addition to tangential rule-making bodies and academics with understanding of proper environmental risk testing, in the proposed Phase II work to speed up commercialization.