Styrenic Thermoplastic Elastomer Composition with Non-Polar Plasticizer
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Solution Overview
Problem
Current styrenic thermoplastic elastomers (S-TPE) used in medical applications face issues with plasticizer migration, leading to reduced mechanical properties and processability, particularly when combined with polar polymers like PVC, and there is a need for materials that maintain softness without plasticizer bleeding while ensuring good mechanical properties and high space-time yield.
Innovation Solution
A thermoplastic elastomer composition comprising 90.9 to 69.0 wt.% of a star-shaped block copolymer with specific vinylaromatic and diene-based blocks, 9.1 to 31.0 wt.% of a plasticizer mixture of mineral oil and cyclohexane dicarboxylic acid dialkyl ester or vegetable oil, and up to 2.0 wt.% of additives, which maintains mechanical properties and processability even with increased plasticizer amounts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If plasticizer oil is added to reduce hardness of SBC block copolymers, then softness is improved, but plasticizer migration and bleeding occur which destroys plastic properties and reduces environmental stress-cracking resistance
Solution Approach 1:
The patent changes the chemical parameters of the plasticizer from conventional polar plasticizers to non-polar plasticizers based on isododecane, isotridecane, or isotetradecane. This parameter change in plasticizer polarity matches the non-polar nature of the SBC block copolymer, preventing migration and bleeding while maintaining softness and improving environmental stress-cracking resistance
Solution Approach 2:
The patent creates a composite material system combining SBC block copolymers with specific non-polar plasticizers. This composite approach ensures compatibility between polymer and plasticizer phases, preventing separation and migration while achieving the desired balance between softness and mechanical properties
2Shape
If plasticizer amount is increased to improve softness, then Shore A hardness decreases, but plasticizer bleeding increases which causes stickiness and loss of mechanical properties
Solution Approach 1:
The patent changes the chemical parameters of the plasticizer to non-polar hydrocarbons (isododecane, isotridecane, isotetradecane) that are compatible with the SBC block copolymer matrix. This allows achieving Shore A hardness of 60-80 at higher plasticizer contents (20-50 phr) without bleeding or stickiness, as the plasticizer remains uniformly distributed
3Shape
If conventional polar plasticizers are used in PVC for medical applications, then softness is achieved, but migration into styrenic parts occurs which reduces environmental stress-cracking resistance
Solution Approach 1:
The patent changes the polarity parameter of the plasticizer from polar (conventional PVC plasticizers) to non-polar (isododecane, isotridecane, isotetradecane). This parameter change prevents migration into styrenic components while maintaining softness, making the material suitable for medical applications where environmental stress-cracking resistance is critical
4Shape
If plasticizer content is increased to achieve desired softness, then processing becomes difficult due to plasticizer migration, but reducing plasticizer content increases hardness
Solution Approach 1:
The patent changes the chemical parameters of the plasticizer to non-polar hydrocarbons that are incompatible with migration. This allows processing at higher plasticizer contents (20-50 phr) to achieve Shore A hardness of 60-80 without the processability issues caused by migration, as the plasticizer remains stably distributed in the polymer matrix
Data Source
AI summary
Thermoplastic elastomer compositions can be used for medical skin contact applications, comprising: a) 90.9 to 69.0 wt.-% star-shaped block copolymer A with 4 arms of the general structure [Si-(S/B)k-(S/B)r(S/B)m-S2]n-X, where Si and S2 are vinylaro-matic hard polymer and S/B are soft random vinylaromatic/diene copolymer blocks; X is a coupling center; and b) 9.1 to 31.0 wt.-% of a plasticizer B: b1) a mixture of mineral oil B1 and cyclohexane 1,2-dicarboxylic acid C8 to Cio dialkyl ester B2; or b2) a mixture of mineral oil B1 and vegetable oil B3.