Mimicking the velcro system from the nature for an alternative rubber/silica coupling system

Bands from unsaturated carbon-carbon chain: 993 cm-1_{, 909 cm}-1

Mimicking the velcro system from nature for an alternative rubber/silica coupling system

Rafal Anyszka

_{, Wilma Dierkes}

_{, Dariusz M. Bielinski}

_{, Essi Sarlin}

_{, Karolina Beton}

_{, Anke Blume}

1

_{University of Twente, Faculty of Engineering Technology, Department of Mechanics of Solids, Surfaces & Systems (MS3),}

Chair of Elastomer Technology & Engineering, Enschede, The Netherlands – r.p.anyszka@utwente.nl

2

_{Lodz University of Technology, Faculty of Chemistry, Institute of Polymer and Dye Technology, Lodz, Poland – rafal.anyszka@p.lodz.pl}

_{Tampere University of Technology, Department of Materials Science, Tampere, Finland}

Supramolecular velcro

recovery of their cohesive (single-component system) or adhesive (two-component system) strength at room temperature by means of supramolecular interactions.

Supramolecular velcro mechanism

Oligomer brushes/elastomer matrix entanglements

1. Reaction between isocyanate silane and mono-functional

telechelic butadiene oligomer with high amount of vinyl groups _{2. Grafting of the reaction product onto the silica} surface by silanol/alcoxyl groups condensation

3. Branching the oligomer backbone with different thiols reactive towards vinyl groups

4. Hydrogenation of the remaining unsaturated bonds4

References:

1. Van Krevelen D. W. (1997) Properties of Polymers 3rd _{Edition, Chapter 7: Cohesive Properties and Solubility:}

189-225.

2. Gutsmann T., Hassenkam T., Cutroni J. A., Hansma P. K. (2005) Sacrificial Bonds in Polymer Brushes from Rat Tail Tendon Functioning as Nanoscale Velcro, Biophysical Journal, 89(1): 536-542.

3. O’Connor K. P., McLeish T. C. B. (1993) „Molecular Velcro”: Dynamics of a Constrained Chain into an Elastomer Network. Macromolecules, 26: 7322-7325.

4. Lin F., Wu C., Cui D. (2017) Synthesis and Characterization of Crystalline Styrene-b-(Ethylene-co-Butylene)-b-Styrene Triblock Copolymers, Journal of Polymer Science, Part A: Polymer Chemistry, 55: 1243-1249.

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Figure 1: Scheme of the supramolecular velco mechanism on silica filler/elastomer matrix interphase. Long oligomer hooks attached to the silica surface form anchor-like connections with cross-linked

elastomer loops by good mutual miscibility, velcro entanglements and stearic hindrance (A). The interphase undergoes disconnection under external stress (B). After the stress relaxation (C) the interphase is able to full recovery into original structure by re-entanglement of mutually miscible hooks-and-loops (D).

Chemical pathway of the oligomer brush (molecular hooks) synthesis on silica surface

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Beside carbon black, silica becomes the most important filler for high-performance rubber products. However, unlike carbon black its surface properties are not favorable for providing satisfactory rubber/filler interactions. A significant amount of silanol groups present on the silica surface results in a considerably polar character, whereas most of rubbers exhibit a non-polar or relatively low-polar character. Because of this, various approaches towards different surface treatments of silica were made.

The aim of this research is to introduce an alternative type of rubber/silica coupling inspired by the velcro system existing in nature. The bio-mimicking mechanism is based on physical entanglements and steric hindrance between mutually soluble (based on calculated solubility parameters1_{): cross-linked and entangled rubber}

macromolecules – acting as molecular loops - and oligomer brushes grafted onto the silica surface – acting as molecular hooks. This results in the formation of supramolecular hooks-and-loops, a rubber/silica interphase fastener exhibiting reconnectable performance (Figure 1).

Introduction:

Solubility parameter– 16.42 J1/2_/cm3/2 Solubility parameter– 17.00 J1/2/cm3/2

Solubility parameter– 16.50 J1/2_/cm3/2

isocyanate

urethane

Figure 2: Progress of the reaction between the

isocyanate silane and butadiene oligomer.

Figure 4: TGA analysis of the silicas modified with

the oligomer brushes.

Figure 3: FTIR spectra of the silica before and

after grafting the oligomer backbone.

Rubber type Solubility parameter (J1/2_/cm3/2₎

BR (100 % vinyl) 15.83 BR (100 % cis/trans) 15.67

IR 18.12

s-SBR (Buna SL 4525-0) 16.23

Table 1: Calculated solubility parameters1_for

various rubbers

Summary and conclusions:



system from nature, a synthesis for supramolecular hooks was developed by grafting long branched-oligomer molecules at the silica surface, which exhibit high chemical affinity to commonly used non-polar rubber acting as a loops.



implementation of alternative filler/elastomer coupling featuring reconnectable interphase interactions.

A

B

C

D

Oligomer brushes (hooks)

Cross-linked elastomer matrix (loops)

Cross-links

The differences and similarities between microscopic and supramolecular velcro systems

Microscopic velcro

Supramolecular velcro

Superior fatigue resistence

Superior reconnectability performance Good mechanical properties

Good ageing resistance

Hooks and loops materials chemical compatibility Not relevant Very relevant