Tire Tread Silica Segmentation for Stiffness and Rolling Resistance
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Solution Overview
Problem
The hydrophilic nature of precipitated silica in rubber compositions leads to filler-filler interactions rather than filler-polymer interactions, resulting in inefficient mixing and reduced reinforcement, which challenges the enhancement of low strain stiffness in tire tread rubber compositions without compromising rolling resistance.
Innovation Solution
Incorporating a combination of pre-hydrophobated and hydrophilic precipitated silica, along with functionalized elastomers and optional silica coupling agents, to create a novel reinforcement network that promotes effective filler-polymer interaction, and potentially adding short fibers or in situ formed resins to enhance low strain stiffness while maintaining rolling resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If pre-hydrophobated precipitated silica is used to promote filler-polymer interaction, then reinforcement is improved, but low strain stiffness is reduced
Solution Approach 1:
The silica system is segmented into two distinct populations: pre-hydrophobated silica (30-70 phr) that provides reinforcement through filler-polymer interaction, and hydrophilic silica (0-70 phr) that maintains low strain stiffness through filler-filler interactions. This segmentation allows each silica type to fulfill its specific functional role without compromising the other property.
Solution Approach 2:
Different regions of the rubber composition exhibit different interaction mechanisms: areas with pre-hydrophobated silica show strong filler-polymer interaction for reinforcement, while areas with hydrophilic silica show filler-filler aggregation that maintains stiffness at low strains. This local quality differentiation resolves the contradiction between reinforcement and low strain stiffness.
2Strength
If functionalized elastomer is used to react with hydroxyl groups on precipitated silica, then filler-polymer interaction is promoted, but available hydroxyl groups are reduced
Solution Approach 1:
The pre-hydrophobated silica is pre-treated with silane coupling agents before incorporation into the rubber composition. This preliminary action creates a hydrophobic surface that promotes filler-polymer interaction through the functionalized elastomer's functional groups, while the remaining hydroxyl groups on hydrophilic silica maintain filler-filler interactions for stiffness.
Solution Approach 2:
The functionalized elastomer acts as an intermediary that bridges the hydrophobated silica surface and the rubber matrix. The functional groups on the elastomer (such as silane, hydroxyl, or carboxyl groups) react with the hydroxyl groups on pre-hydrophobated silica, creating a strong interface while allowing the bulk polymer to maintain its properties.
3Strength
If silica coupling agent is added to promote filler-polymer coupling, then reinforcement is improved, but mixing efficiency is reduced
Solution Approach 1:
The silane coupling agent is applied to the silica surface in advance during the pre-hydrophobation step, before the silica is incorporated into the rubber composition. This preliminary coupling reduces the need for additional coupling agents during mixing, thereby maintaining mixing efficiency while ensuring adequate filler-polymer coupling.
Solution Approach 2:
The pre-hydrophobated silica already contains grafted silane coupling agents from the pre-treatment step, allowing it to self-couple with the functionalized elastomer without requiring additional coupling agents during the rubber compounding process. This self-service approach maintains mixing efficiency while achieving reinforcement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly increases low strain stiffness and improves wet and dry handling performance of tire treads while maintaining or reducing rolling resistance, as demonstrated by various experimental rubber compositions.
Implementation Method 1
functional groups reactive with hydroxyl groups on the precipitated silica to promote its coupling to the diene-based functionalized elastomer(s)
Implementation Method 2
a silica coupler, or silica coupling agent, having a moiety, such as for example an alkoxysilane component, reactive with hydroxyl groups (e.g. silanol groups) on the precipitated silica
Implementation Method 3
pre-hydrophobating the hydrophilic precipitated silica by pre-treating the precipitated silica prior to its addition to the rubber composition
Data Source
AI summary
The invention relates to a rubber composition and tire with tread thereof containing a functionalized elastomer and reinforcement comprised of rubber reinforcing carbon black and a combination of pre-hydrophobated precipitated silica and at least one of hydrophilic precipitated silica together with at least one of short fibers and resin product of methylene acceptor and methylene donor or hydrophilic precipitated silica having been hydrophobated in situ within the rubber composition by a silica coupling agent, optionally together with at least one of reinforcement additive comprised of short fibers and reinforcement additive comprised of resin product of methylene acceptor and methylene donor.