Polymer-Solid Interface Connectivity and Adhesion: Design of a Bio-Based Pressure Sensitive Adhesive

Abstract

Abstract:Adhesion at polymer-solid interfaces was explored for a new bio-based pressure sensitive adhesive (PSA) in terms of sticker groups φ X on the polymer phase, receptor groups φ Y on the solid surface and the bond strength of the sticker-receptor X-Y acid-base interaction, χ. The polymer-solid interface restructuring models of Gong and Lee et al were extended with new percolation models of entanglements and interface strength to determine the optimal sticker group concentration φ* X . For the general case where φ Y and χ are constant, it is predicted that when φ X < φ* X , that the critical peel energy behaves as G 1c ~ φ X /φ* X and the locus of failure is adhesive between the polymer and the solid.However, when φ X > φ* X , failure occurs cohesively in a polymer-polymer interface adjacent to the solid and the strength decreases as G 1c ~ φ* X /φ X . The switch from adhesive to cohesive failure can be understood in terms of the changes in the chain conformations of the adhered chains and their decreasing interpenetration X i with the bulk chains, via X i ~ 1/r, where r = χφ X φ Y . The optimal value of φ X which maximizes the adhesion and determines the mode of failure is given by φ* X ≈0.129/C ∝ , and for typical values of the characteristic ratio C ∝ in the range 7-20, φ* X ≈ 1% mole fraction, corresponding to about 2 sticker groups per entanglement molecular weight M e . This result was verified for a biobased pressure sensitive adhesive synthesized from an acrylated high oleic fatty acid, which was copolymerized with maleic anhydride as the sticker group. The observed behavior is counterintuitive to the current wisdom for the effect of acid-based interactions on adhesion, where the strength is expected to increase with the number of X-Y contacts. The surprisingly low value of φ* X ≈ 1% sticker groups which maximizes the adhesion strength can now be readily calculated using the percolation model of entanglements and fracture.

Self-healing materials: a review

“…In a seminal study, Kausch and co-workers [13][14][15] showed that single cracks that were formed at room temperature in fracture mechanics specimens of PMMA could be completely rehealed when the surfaces were rejoined and welded above the glass transition temperature T g . Much work has been done by our group [16][17][18][19][20][21][22][23][24][25] and others to understand the concept of strength development at polymer-polymer interfaces and polymer-solid interfaces [69][70][71][72][73][74][75] in terms of the fundamental dynamics of entangled polymers. Using DeGennes' reptation dynamics and the entanglement percolation model, 17,76 we derived a unified theory for the strength development of polymer-polymer interfaces.…”

“…When a mole fraction of sticker groups f(X) is used to bond the polymer to the surface, an optimal sticker group concentration f*(X) is needed to maximize adhesion while minimizing cohesive failure in the boundary layer adjacent to the solid. [69][70][71][72][73][74][75] When f < f*, adhesive failure dominates, the fracture energy G 1c $ f and the solid separates cleanly from the polymer. When f > f*, cohesive failure occurs in a polymer layer adjacent to the surface and G 1c $ 1/f.…”

“…Since C f is of order 7-20 for many polymers, then f* $ 1%, as observed. [69][70][71][72][73][74][75] Thus, in the presence of a healing fluid, surface restructuring would produce a new value of f* which is considerably less than the original. The resulting restructuring could result in a very weak polymer-solid interface since the weak cohesive failure mode would be favored.…”

Flame-Retardant Pressure-Sensitive Adhesives Derived from Epoxidized Soybean Oil and Phosphorus-Containing Dicarboxylic Acids

“…Pressure-sensitive adhesives (PSAs) are special types of adhesives that form a bond when external pressure is applied to make the adhesive cling to the adherend. Because of their soft nature and liquid viscoelasticity, they can form a contact with rough and nonwetting surfaces. − According to the required technical specifications, such as permanent or removable applications, PSAs must bond materials efficiently in a fast and safe way. − Except for natural rubbers, PSA categories are still based on petroleum. − Polymers derived from renewable resources have recently experienced a remarkable resurgence because of long-term environmental and availability concerns associated with petroleum derivatives. , Among the different kinds of renewable raw materials, plant oils are currently one of the most abundant, most biodegradable, least toxic, and cheapest renewable raw materials, which have been widely used as promising monomers of thermosetting composites in various applications such as foams, elastomers, coatings, and paints. − In addition, the long aliphatic chains of the fatty acids impart unique properties to the resulting polymeric materials such as elasticity, flexibility, hydrolytic stability, hydrophobicity, and low glass transition temperatures ( T g ), making them suitable for PSAs. − Li and co-workers , obtained PSAs by reacting ESO with at least one dibasic acid (e.g., sebacic acid) or anhydride at molar ratios ranging from 3:1 to 1:3. The subsequent curing led to a tacky coating that had good adhesive properties for various substrates.…”

Recent synthetic approaches and emerging bio‐inspired strategies for the development of sustainable pressure‐sensitive adhesives derived from renewable building blocks

“…In a different approach, Wool and Bunker reported PSA compositions containing acrylated methyl oleate (AMO; Figure ), a fatty biobased monomer obtained by the acrylation of the epoxidized form of methyl oleate, the later compound being prepared by transesterification of plant oils such as high‐oleic soybean oil. This monomer proved to be suitable for solvent‐free waterborne latex processes and to have comparable adhesive properties as petroleum‐based polymers . Another family of UV‐polymerizable adhesive compositions containing acrylated monounsaturated fatty acid alkyl esters was also reported and included monomers such as acrylated methyl margaroleate (margaroleic acid is a C 17 :1 fatty acid), acrylated methyl palmitoleate (C 16 :1), acrylated methyl myristoleate (C 14 :1), acrylated methyl gadoleate (C 20 :1), and acrylated methyl eruceate (C 22 :1) .…”