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Introduction to Waterborne Polyurethanes
Published in Ram K. Gupta, Ajay Kumar Mishra, Eco-Friendly Waterborne Polyurethanes, 2022
Felipe M. de Souza, Prashant Kote, Ram K. Gupta
To find an alternative, researchers developed an approach that used soybean oil for the synthesis of WPU [5]. The synthesis consisted of performing a ring-opening reaction of epoxidized soybean oil with adipic and pimelic acid, separately, to introduce a carboxylic acid as an ionic segment. The synthesized WPU was used as a pressure-sensitive adhesive. Shear strength of about 1 h to more than 100 h, a tack of 1.78–5.66 N, and peel strength of 1.23–2.77 N/mm were observed for this adhesive. Castor oil was used as a natural polyol source and provided a total bio content of about 77% in the WPU. Also, castor oil demonstrated good compatibility with the bio-derived ionic segments. The results demonstrated that the WPU obtained through the emulsification process had effective thermal stability that presented the max thermal decomposition temperature (~383°C) along with good adhesive characteristics. These properties, accompanied by renewable sources of materials, show potential for large-scale applications.
Principles of Adhesive Rheology
Published in Nicholas P. Cheremisinoff, Elastomer Technology Handbook, 2020
Rubber also helps to establish effective intermolecular diffusion friction force at the interface. Adhesive bond formation to the substrate can be assisted by combining the rubber with other components such as tackifiers and plasticizers. These substances help to increase the compliance of this type of adhesive. Pressure-sensitive adhesive creeps under applied stresses. Once this occurs, the rubber component engages in effective molecular mutual entanglement at the interface. In Section ILA, we mentioned that molecular entanglement of high molecular weight polymers at the interface provides ideal molecular link functionality. Because of such entanglements, the mechanical forces can be effectively transferred across the interface. It is interesting to note that typical rubbers have molecular weights in the range 105 to 106, which is several orders of magnitude higher than the other components of the adhesive.
Polymers-Based Devices for Dermal and Transdermal Delivery
Published in Severian Dumitriu, Valentin Popa, Polymeric Biomaterials, 2020
Donatella Paolino, Margherita Vono, Felisa Cilurzo
Polyisobutylene, produced by low-temperature cationic polymerization, is a polymer with no asymmetric carbons (Figure 28.8). In its unstrained state, the polymer is in an amorphous state, and its Tg is ∼70°C (Wood 1976). Its physical state changes at the increase of molecular weight. Low molecular weight polymers are viscous liquids, and at the increase of molecular weight, they become more viscous to reach elastomeric solids. Un-crosslinked polymers exhibit a high degree of self-adhesion and for this reason they have been largely used as pressure-sensitive adhesive. (Qvist et al. 2002, Schulz et al. 2010).
On stickiness of multiscale randomly rough surfaces
Published in The Journal of Adhesion, 2021
G. Violano, L. Afferrante, A. Papangelo, M. Ciavarella
Contact mechanics with roughness has made tremendous progress in recent years (for two recent reviews, see Refs. [1,2]), and adhesion has become increasingly relevant with the interest on soft materials,[3] nano-systems[4,5] and the analysis of bio-attachments.[6,7] Contact between solids occurs via large van der Waals forces, usually represented, for example, by the well-known Lennard–Jones force-separation law. These forces give rise to a theoretical strength much higher than the typical values to break bulk materials apart. Hence, the “adhesion paradox”[8] states that all objects in the Universe should stick to each other. This does not happen due to inevitable surface roughness at the interface, and Nature has developed different strategies to achieve stickiness, including contact splitting and hierarchical structures.[9–11] At macroscale and for nominally flat bulk solids, it appears that the only solution to maintain stickiness is to reduce the elastic modulus. This is well known in the world of pressure-sensitive adhesives (PSA), soft polymers showing instantaneous adhesion on most surfaces, upon application of just a light pressure.[12,13] Dahlquist[14,15] proposed that to achieve a universal stickiness, the elastic Young modulus should be smaller than about 1 MPa (at 1 Hz, as adhesives are strongly viscoelastic, their modulus depends on frequency). This criterion has no scientific validation but appears to be largely used in the world of adhesives.