Pressure-sensitive Adhesives Research Articles

Synthesis and reactivity of novel cinnamonitrile derivatives as reactive UV stabilizers for enhanced light protection and performance of coatings

Ultraviolet (UV) light is generally harmful to human health and organic compounds (for example, plastics) as it deteriorates the long-term stability via photodegradation. Thus, an efficient strategy for reducing light-induced damage is the key to maximizing the operation lifetime or durability of materials. The most common means of preventing UV light-induced damage is by adding compounds that possess excellent UV absorbing capability. In this study, novel cinnamonitrile derivatives were designed and synthesized for their application as UV absorbers in pressure-sensitive adhesives. Absorption wavelengths were finely tuned by simple structural modification, and better molar absorptivity was obtained. The hydroxyhexyl functional group affixed into the cinnamonitrile core granted superior solubility (>10 wt%) in common organic solvents and acrylic monomers/resins, instigating enhanced UV blocking and visible light transparency. Further, to enhance the solubility and long-term stability of UV absorbers within a network, hydroxyhexyl-functionalized cinnamonitrile UV absorber was incorporated into urethane-based crosslinkers. Covalently attached reactive UV absorbers improved the adhesion property even at a high loading of UV absorber and remarkable physical persistence within the network.

Two-functional phase-change pressure-sensitive adhesives based on polyisobutylene matrix filled with paraffin wax

Paraffin wax was used to impart the function of heat accumulation to pressure sensitive adhesives based on polyisobutylene (PIB) and simultaneously to suppress their cold flow. Laser microinterferometry showed 6% solubility of paraffin wax in PIB at 25 °C with achieving complete miscibility of PIB and wax at temperatures above 46 °C. The thermophysical and rheological properties of mixtures containing from 10% to 60% paraffin wax were investigated. According to calorimetry data, wax reduces the glass transition temperature of PIB, which in turn affects the apparent degree of wax crystallinity, shifting it in different directions. Paraffin wax significantly reduces the effective viscosity of the PIB melt and lowers the values of its storage and loss moduli. This simplifies the processing of adhesives and allows them to be used as easily flowable liquids. Nevertheless, the wax crystallizes during cooling, which leads to a multiple increase in the viscosity of adhesives to a level comparable or even greater than the viscosity of filler-free PIB. In this process, the heat is released in relatively larger quantities than during crystallization of pure wax, as additional heat is produced owing to the loss of solubility of wax in the PIB matrix. With an increase in the wax content, the durability of adhesive joints with steel firstly passes through a minimum, which is associated with the plasticizing effect of paraffin wax. However, the addition of 60% paraffin wax makes it possible to increase the durability of adhesive joints by 20 times, simultaneously reducing the melt viscosity of the adhesive by 4 decimal orders of magnitude. A key fact is that the resulting easy-to-process adhesive allows storing heat, i.e. to play two roles at the same time – a reinforced pressure-sensitive adhesive and a phase-change material.

UV curable, flame retardant, and pressure-sensitive adhesives with two-way shape memory effect

Novel UV curable acrylic pressure-sensitive adhesives (PSAs) with exceptional flame retardancy and promising two-way shape memory effect have been developed using a commercial diethyl phosphoramidate as multifunctional tackifier for the first time. The abundant hydrogen bonds and high viscosity of the resultant networks contribute to the low temperature and repeatable adhesions. The PSA with 5 wt % tackifier exhibited the best overall adhesion at both 25 °C and 0 °C, especially with the relatively high peak adhesive stress and the highest work of adhesion. Owing to the synergistic effect with nitrogen containing acylate monomer, the 15 wt% diethyl phosphoramidate endowed the PSA sample with self-extinguishing ability. Moreover, the higher viscoelasticity makes the tackified PSAs with better two-way shape memory property. In particular, the elongation upon cooling and contraction upon heating are 57.2% and 55.9%, respectively. • A multifunctional tackifier for acrylic pressure-sensitive adhesives is reported. • The PSAs integrate UV curability, flame retardancy, and two-way shape memory effect. • A condensed phase flame retardant mechanism of phosphoramidate is proposed. • The higher viscoelasticity suggests better two-way shape memory property. • Two-way shape memory effect in cyclic freezing and thawing scenario is demonstrated.

Laser-induced graphene composite adhesive tape with electro-photo-thermal heating and antimicrobial capabilities

Laser-induced graphene (LIG) and its composites have been demonstrated to be useful in broad-reaching applications such as water and air filtration and sensors. A main advantage of LIG is the embedding of conformal graphene foam in any design into polymeric substrates. However, embedded LIG must be detached from the substrate for a composite nanomaterial, and delamination of LIG has been demonstrated. Here, we incorporated LIG as a composite into a double-sided tape using pressure-sensitive adhesives and delamination from the substrate, and demonstrated its use for electro-photo-thermal applications, including bacterial inactivation. LIG was transferred onto thermally conductive pressure-sensitive adhesive containing carbon black, and a double-sided sticky tape was prepared by sandwiching perforated tissue adhesive between two LIG layers, giving enhanced electrical conductivity in the x, y, and z directions compared to commercial carbon tape. The LIG composite tape showed excellent electrothermal properties with a maximum temperature >120 °C at 10 V and a temperature rise >70 °C under 120 mW/cm2 solar irradiation. The same electrothermal activity was observed after 50 heating and cooling cycles and reached a temperature of ∼111 °C. Bacterial inactivation was observed on the surface of the LIG composite tape at ∼3.5 V, and electro- and photothermal effects caused sterilization of the surfaces up to 99.99%. These electrically conductive LIG composite adhesive tapes might be used in electronic applications for heating surfaces at low voltages (<9 V) or to prevent surface biofilm or microbial growth.

Tuning adhesion performance of an acrylic pressure‐sensitive adhesive using polysilsesquioxane‐acrylic core‐shell nanoparticles

AbstractSurface migration of unmodified inorganic or polymer core‐inorganic shell nanoparticles has limited their application for improvement of pressure‐sensitive adhesives (PSAs) properties. The efficiency of utilization of modified inorganic nanoparticles with sticky polymer brushes was investigated to overcome this problem. For this purpose, polymethacryloxypropylsilsesquioxane‐acrylic core‐shell (CS) nanoparticles were synthesized and added to poly(methyl methacrylate‐co‐butyl acrylate) (MBC) acrylic PSA through latex blending. Using CS nanoparticles, a concomitant increase in the peel and shear strengths of the acrylic PSA was achieved, and also the limitation of surface migration of nanoparticles at high volume fractions was overcome. Moreover, CS nanoparticles acted as a compatibilizer for MBC chains, rich in methyl methacrylate (MMA) or butyl acrylate (BA). These MMA‐rich and BA‐rich chains were formed during the synthesis of MBC latex through batch emulsion copolymerization method, due to the difference in the reactivity ratio of BA and MMA radicals. The compatibility of CS nanoparticles with each of the components of MBC was systematically investigated in terms of grafting density, swelling ratio, and thermodynamic affinity and was correlated to the final properties.

Characterization of different types of lignin and their potential use in green adhesives

Lignin is the second most abundant component of lignocellulosic biomass after cellulose. This aromatic polymer has an immense potential for applications in composite materials, organic synthesis and pharmaceutical industries. In this study, different types of lignin (Kraft and three organosolv lignins from different processes) were characterized and incorporated into a pressure sensitive adhesive (PSA) aqueous formulation based on polycarboxylate polyether (PCE), which was selected for its low ecotoxicity. All lignin samples were evaluated and compared using various characterization methods, such as GPC, 13C NMR and 31P NMR spectroscopy. Thermal properties were investigated using TGA and DSC techniques. Based on these analyses, organosolv lignin samples presented lower molecular weight (Mw), lower polydispersity and higher amounts of phenolic OH groups. Optimizing molecular weight and hydroxyl contents were found to be the main factors affecting PSA properties. One of our formulations (5-OL-B2), which incorporated the organosolv lignin of lowest molecular weight (Mw ≈ 1270 g/mol) and highest OH content (~7.08 mmolOH/glignin), leads to an adhesive performance similar to that the commercial PSA, such as low peel-off losses and lower distance traveled by the ball (higher tackiness).

Effect of silane acrylate on the surface properties, adhesive performance, and rheological behavior of acrylic pressure sensitive adhesives for flexible displays

In this study, novel silane acrylates, urethane silane acrylate (USA) and urethane silane linear acrylate (USLA), comprised of urethane and silane groups were designed and synthesized, and their effect on the surface properties, adhesion, and rheological behavior of acrylic PSA was evaluated. The introduction of the synthesized USA and USLA affected the chain arrangement, and at least 3 wt% of the silane acrylates was required to alter the surface properties (roughness and wettability). Compared to a commercial silane acrylate (SA), USA and USLA showed improved cohesion of the acrylic PSA aided by the urethane bond; however, the length of the terminal silane groups produced some variations. USA improved the cohesive properties of acrylic PSA due to its short chain, which further increased the peel strength of the acrylic PSA as compared to USLA (USA: 1363 ± 173 gf/25 mm, USLA: 1258 ± 132 gf//25 mm, based on 1 wt% content). However, at 3 wt% or more, excessive cohesion led to a decrease in the interaction with the substrate, thereby decreasing the peel strength. On the other hand, SA gradually increased the peel strength of the acrylic PSA, but cohesive failure occurred due to the insufficient increase in the cohesion. With respect to the flexibility of the acrylic PSAs, SA slightly improved the modulus of the high-temperature region aided by the silane group, and the recovery properties were increased from 10.8% to a maximum of 31% at 100% strain. In addition, the low cohesive properties resulted in very high stress relaxation properties (>99%). The effects of USA and USLA on flexibility were similar, but the high cohesive force further improved the elastic properties, resulting in better recovery than those imparted by SA (USA: 87 ∼ 89.4%, USLA: 56.6 ∼ 91.7%). Comparing the two urethane-based silane acrylates, the stress relaxation property of USA was lower than that of USLA, which is related to the cohesive property of the acrylic PSA. In addition, all of the synthesized acrylic PSAs showed excellent optical properties with transmittance >98.1% and haze <2.23%, indicating their potential for application in flexible displays.

RheoTack—An approach to investigate retraction rate dependent detaching behavior of pressure sensitive adhesives

Characterization methods of pressure sensitive adhesives (PSA) originate from technical bonding and do not cover relevant data for the development and quality assurance of medical applications, where PSA with flexible backing layers are adopted to human skin. In this study, a new method called RheoTack is developed to determine (mechanically and optically) an adhesion and detaching behavior of flexible and transparent PSA based patches. Transdermal therapeutic systems (TTS) consisting of silicone-based PSAs on a flexible and transparent backing layer were tested on a rotational rheometer with an 8 mm plate as a probe rod at retraction speeds of 0.01, 0.1, and 1 mm/s with respect to their adhesion and detaching behavior in terms of force-retraction displacement curves. The curves consist of a compression phase to affirm wetting; a tensile deformation phase intercepting stretching, cavity, and fibril formation; and a failure phase with detaching. Their analysis provides values for stiffness, force, and displacement of the beginning of fibril formation, force and displacement of the beginning of a failure due to fibril breakage and detaching, as well as corresponding activation energies. All these parameters exhibit the pronounced dependency on the retraction speed. The force-retraction displacement curves together with the simultaneous video recordings of the TTS deformation from three different angles (three cameras) provide deeper insight into the deformation processes and allow for interpreting the properties’ characteristics for PSA applications.

Influence of modified attapulgite on silicone pressure-sensitive adhesives properties

Influence of modified attapulgite on silicone pressure-sensitive adhesives properties

Sustainable terpene triblock copolymers with tuneable properties for pressure sensitive adhesive applications

A series of triblock copolymers in a hard-soft-hard block configuration with varying hard block α-pinene methacrylate content and molecular weight and butyl acrylate soft segment have been synthesised and investigated for viability in pressure sensitive adhesive (PSA) applications. The morphologies vary from pockets of hard phase distributed within a continuous soft matrix, through to lamellar with co-continuous phases, and finally continuous hard phase with pockets of soft phase dispersed. Uniaxial tensile properties, probe adhesion performance and cyclic adhesive behaviour are presented for seven compositions including four short chain and three long chain copolymers, alongside a commercial benchmark PSA. Structure-property relationships for the novel elastomers are evaluated, establishing that short chain materials with 20–25 wt% poly(α-pinene methacrylate) offer similar tensile and adhesion performance to the commercial elastomer. Raising the hard phase concentration has been observed to provide a considerable increase in ultimate tensile strength, stiffness and peak tack force, but at the expense of significant reductions in ultimate tensile strain, adhesive bond displacement and vibrational dissipation. The results suggest that the performance of these sustainable materials can be tuned to produce viable PSAs with a range of useful properties.

Rational Design of Waterborne Polyurethane Pressure Sensitive Adhesives for Different Working Temperatures.

The appropriate pressure sensitive adhesion performances at working temperature are vital for the applications of waterborne polyurethane (WPU). Understanding the relationship among rheological behaviors, macromolecular structures and adhesive performances can be very useful to the rational design of waterborne polyurethane pressure sensitive adhesives (WPU-PSAs) for different operating temperatures, as well as other kinds of adhesives. In this study, four kinds of WPU-PSAs were prepared by reacting polypropylene glycol (PPG), hydrogenated hydroxyl-terminated polybutadiene (HHTPB), dimethyl alcohol propionic acid (DMPA), 1,6-hexamethylene diisocyanate (HDI) and four kinds of chain extenders. Gel permeation chromatography (GPC), swelling and rheology tests were used in parallel with an analysis of adhesive performances of the dried films of the adhesives. Results showed that, in addition to the nature of chain extenders playing a role on the rheological behaviors and adhesive performances of polymer, the gel content could be used to adjust the macromolecular structure and molecular weight distribution of polymer, thus distinctly affected the adhesive performances of PSA. The relationship among rheological behaviors, macromolecular structure and adhesive performances was investigated, and the rational design of WPU was achieved with appropriate pressure sensitive adhesion properties for different working temperatures of 25 and 60 °C.

Influence of cleaned granite dust on the properties of silicone pressure-sensitive adhesives

The influence of addition cleaned granite dust on self-adhesive products, such as self-adhesive tapes based on silicone pressure-sensitive adhesives was presented. The new way of waste management, is a very important issue in the modern world. The obtained self-adhesive materials were tested both in terms of the properties of adhesive compositions (pot-life test) as well as the influence on the operational parameters of the obtained self-adhesive tapes, such as adhesion, cohesion, stickiness or shrinkage. The obtained results are presented in the paper below.

Influence of Acrylonitrile Content on the Adhesive Properties of Water-Based Acrylic Pressure-Sensitive Adhesives.

A series of pressure-sensitive adhesives (PSA) were prepared by emulsion polymerization in order to obtain a PSA that meet with the current label market requirements. For it, the effect of the incorporation of acrylonitrile (ACN) as hard monomer was investigated in a n-butyl acrylate (n-BA) and acrylic acid (AA) system. Great differences were found in the adhesive performance according to the ACN weight ratio. Its increased resulted in a considerable rise in the average sol molecular weight and in the glass transition temperature. This was reflected in a decrease of adhesion forces (peel resistance and tack) and an increase of the cohesion forces (shear resistance). Moreover, the incorporation of the minimum amount of ACN studied showed a great change in the elastic modulus determined by dynamic shear resistance with respect to the based formulation that did not contain ACN. Finally, the ice bucket test was carried out to check the adhesive performance in cold and wet environments.

Carboxyethyl acrylate incorporated optically clear adhesives with outstanding adhesion strength and immediate strain recoverability for stretchable electronics

Since the development of the 5G network, wireless and user-oriented electronics are rapidly emerging. In response to demands for wearable devices, which are curved, bendable and/or stretchable, all components of electronics are required to be flexible. Moreover, the assembly of these components is challenging issue, because the conventional adhesives used in displays are typically rigid unsuitable for flexible electronics. Therefore, developing elastic pressure-sensitive adhesives (PSAs) is critical for the commercialization of flexible electronics. In this study, UV curable acrylate-based PSAs are synthesized using 2-carboxyethyl acrylate (CEA) as a functional monomer, and exhibit exceptionally strong peel adhesion and good flexibility. The synthesized film also exhibits adequate transmittance (>95%) to be used as an optically clear adhesive. The stress-relaxation and strain-recovery behavior of the PSAs at various conditions is evaluated and analyzed in detail. To induce elastic characteristics in the PSAs, a pre-straining strategy is implemented, which triggers a purely elastic characteristic with instantaneous strain recovery. The pre-strained PSAs were able to withstand 5000 cycles of repetitive stretching and bending tests; thus, the synthesized PSAs can provide wide range of applications, including stretchable displays and epidermal devices.

Influence of Adhesive Tapes as Thermal Interface Materials on the Thermal Load of a Compact Electrical Machine

In this article, a novel form of thermal interface material (TIM), represented by three industrially manufactured pressure-sensitive adhesive (PSA) tapes with electrical insulating properties, is characterized regarding its applicability in an electric motor with air-gap winding. Firstly, the adhesion performances, in terms of the winding process, were investigated experimentally. Here, every TIM shows sufficient shear strength for the wire–TIM joints, as well as peel adhesion to the laminated iron core. Secondly, the thermal–physical properties of the TIMs are inspected experimentally via laser flash analysis (LFA) and differential scanning calorimetry (DSC). For every TIM, the value of the thermal resistance can double if the relatively smooth surface (Ra = 0.2 μm) of the adjacent layers is interchanged with a rougher one (Ra = 2.0–3.7 μm). Additionally, the TIM’s performance at the system level is examined. Therefore, a flat test section, according to the specifications of the original motor, is studied experimentally and numerically utilizing infrared (IR) thermography and the finite element method (FEM). The focus is set on the heat flow and temperature distribution in the test section under varying thermal loads, mass flow, and variety of TIMs.

Acrylic pressure-sensitive adhesives based on ethylene glycol acrylate for flexible display application: Highly elastic and recoverable properties

New acrylic PSAs with a high flexibility were synthesized using 2-(2-ethoxyethoxy)ethyl acrylate (EEA), an ethylene glycol-based acrylate. Compared to acrylic PSAs based on 2-ethylhexyl acrylate (EHA) and octyl acrylate (OA), acrylic PSA based on EEA was found to form physical crosslinking due to improved chain entanglement and increased secondary bonding by the ethylene glycol and hydroxyl groups. These properties showed behaviors similar to those caused by crosslinking, which improved the elasticity of acrylic PSA and resulted in a fast recovery rate and high recovery characteristics of more than 70%. In addition, it was confirmed that the physical crosslinking supplemented the cohesive strength of the acrylic PSA, which showed relatively excellent adhesion properties compared to EHA and OA despite a low modulus of less than 106 Pa. The properties of EEA-based acrylic PSA were controlled by the photoinitiator (PI) and chain transfer agent (CTA), and the effect of reaction conditions on EEA-based acrylic PSA was analyzed based on this. The PI did not affect the molecular weight of the acrylic PSA, and only the reaction rate was controlled by the radical content. On the other hand, the CTA showed sufficient control over the molecular weight and molecular weight distribution of acrylic PSAs. The viscoelastic properties of the acrylic PSA also showed no significant change in response condition control, indicating excellent elasticity, regardless of the conditions. The PI influenced the creep and recovery characteristics of the acrylic PSA through plasticization, and excellent stress relaxation characteristics were confirmed by the controlled glass transition temperature.

Roles of molecular interaction and mobility on loading capacity and release rate of drug-ionic liquid in long-acting controlled release transdermal patch

This study aimed to develop long-acting controlled release transdermal patches containing ionic liquids (ILs) of weak acid drugs and investigate effects of pressure sensitive adhesives (PSAs) on drug-ILs loading and release. Here, ketoprofen, flurbiprofen and loxoprofen were chosen as model drugs, and triethylamine was selected as model counterion. Three types of PSAs containing carboxyl (PSA-COOH), hydroxyl (PSA-OH) and non-functional group (PSA-none) were respectively synthesized. Microscopy results showed that the solubility of drug-ILs in PSA-COOH was enhanced up to 4.50 times compared with that in other PSAs. Drug release results showed that the average release percentage of drug-ILs in PSA-COOH (70.97%) had no significant difference with that in PSA-OH (73.22%) and PSA-none (73.47%). While drug skin penetration performances demonstrated that the average skin flux of drug-ILs in PSA-COOH (23.73 μg/(cm2 h)) was much higher than that in PSA-OH (6.75 μg/(cm2 h)) and PSA-none (4.32 μg/(cm2 h)). As illustrated by FTIR, Raman and DSC analysis, ionic hydrogen bonding determined drug-ILs loadings, and interaction strength between drug-ILs and PSA-COOH was the strongest owing to the deprotonated PSA-COO–. Rheology study revealed that decreased storage modulus and increased phase shift angle of PSA-COOH determined drug-ILs release owing to strong plasticization at high drug-ILs loading. Remarkably, the long-acting controlled release patches were successfully developed and molecular mechanisms were revealed.

Use of pressure sensitive adhesives to create flexible ballistic composite laminates from UHMWPE fabric

Fiber reinforced composites (FRC) have been widely used for ballistic resistance where hot resin melt is infused into the fabric layers and cured to form the composite. Here, we explore the use of pressure-sensitive adhesive (PSA) and its cold lamination as a simple, rapid and inexpensive method to integrate plain-weave UHMWPE and demonstrate that these composites have attractive ballistic performance. Simple compression lamination of 22 layers of fabric with interlay of PSA, for 1 min at 4 or 8 MPa, was able to confer the ability to stop 9 mm bullets shot at ∼357 m/s. Increasing the processing pressure results in an increase of inter-ply bonding strength significantly while only affecting the bending stiffness slightly. It also results in an increase in energy absorption of laminate which leads to smaller backface signature and volume and better ballistic performance. They are also more flexible, thinner and lightweight compared with hot melt FRC.

Crosslinking of Pressure-Sensitive Adhesives with Polymer-Grafted Nanoparticles.

Nanocomposite filler particles provide multiple routes to mechanically reinforce pressure-sensitive adhesives (PSAs), as their large surface area to volume ratios provide a means of effectively crosslinking multiple polymer chains. A major advancement could therefore be enabled by the design of a particle architecture that forms multiple physical and chemical interactions with the surrounding polymer matrix, while simultaneously ensuring particle dispersion and preventing particle aggregation. Understanding how such multivalent interactions between a nanoparticle crosslinking point and the PSA polymer affect material mechanical performance would provide both useful scientific knowledge on the mechanical structure-property relationships in polymer composites, as well as a new route to synthesizing useful PSA materials. Herein, we report the use of polymer-grafted nanoparticles (PGNPs) composed of poly(n-butyl acrylate-co-acrylic acid) chains grafted to SiO2 nanoparticle (NP) surfaces to cohesively reinforce PSA films against shear stress without compromising their adhesive properties. The use of acrylic acid-decorated PGNPs allows for ionic crosslinking via metal salt coordination to be used in conjunction with physical entanglement, yielding 33% greater shear resistance and up to 3-fold longer holding times under static load. In addition, the effects of material parameters such as PGNP/crosslinker loading, polymer graft length, and core nanoparticle size on mechanical properties are also explored, providing insights into the use of PGNPs for the rational design of polymer composite-based PSAs.

Dibutyl Itaconate and Lauryl Methacrylate Copolymers by Emulsion Polymerization for Development of Sustainable Pressure-Sensitive Adhesives.

Renewable polymers possess the potential to replace monomers from petrochemical sources. The design and development of polymeric materials from sustainable materials are a technological challenge. The main objectives of this study were to study the microstructure of copolymers based on itaconic acid (IA), di-n-butyl itaconate (DBI), and lauryl methacrylate (LMA); and to explore and to evaluate these copolymers as pressure-sensitive adhesives (PSA). The copolymer synthesis was carried out through batch emulsion radical polymerization, an environmentally friendly process. IA was used in a small fixed amount as a functional comonomer, and LMA was selected due to low glass transition temperature (Tg). The structure of synthesized copolymers was studied by FTIR, 1H-NMR, Soxhlet extraction, and molecular weight analyses by GPC. Furthermore, the viscoelastic and thermal properties of copolymer films were characterized by DMA, DSC, and TGA. The single Tg displayed by the poly(DBI-LMA-IA) terpolymers indicates that statistical random composition copolymers were obtained. Moreover, FTIR and NMR spectra confirm the chemical structure and composition. It was found that a cross-linked microstructure and higher molecular weight are observed with an increase of LMA in the feed led. The Tg and modulus (G′) of the copolymers film can be tuned with the ratio of DBI:LMA providing a platform for a wide range of applications as a biobased alternative to produce waterborne PSA.