Pressure-sensitive Adhesives Research Articles

Exploiting the lower disorder-to-order temperature in polystyrene-b-poly(n-butyl acrylate)-b-polystyrene triblock copolymers to increase their flow resistance at high temperature

This work focuses on the temperature-dependent structural and rheological characterization of polystyrene-b-poly(n-butyl acrylate)-b-polystyrene triblock copolymers (PS-b-PnBA-b-PS) in the melt and, in particular, on their ability to show a lower disorder-to-order temperature (LDOT). To this aim, copolymers of varying block lengths, but keeping the PnBA block as a major component, were synthesized. Small-angle x-ray scattering revealed that the copolymers with short PS blocks (∼10 kg/mol) approach an LDOT but do not cross it. At room temperature, these copolymers exhibit higher moduli compared to a PnBA homopolymer due to the reinforcing effect of the PS but are flowing at temperatures above the glass transition of the PS. Increasing the PS and PnBA block length, to keep the same PS fraction, induces more profound changes in the structural and viscoelastic behaviors. Such a copolymer crosses the LDOT, leading to a microphase-separated and ordered state at high temperature. Contrary to the copolymers with short PS blocks, the flow regime was not reached, even at temperatures well above the glass transition of the PS. Instead, a low-frequency plateau was observed in rheology, showing the increased lifetime of the microphase-separated PS domains. ABA triblock copolymers exhibiting an LDOT behavior could, thus, be of interest for the design of thermoplastic elastomers or pressure-sensitive adhesives that can resist the flow at high temperatures.

Tailoring the linear viscoelastic response of industrial double dynamics networks through the interplay of associations

We investigate the linear viscoelastic properties of industrial pressure sensitive adhesives comprising double networks with an entangled acrylate-based polymer and two types of intermolecular associations (crosslinking), permanent (epoxide) and reversible (metal-chelate), having different compositions. A combination of shear rheometry and an appropriately modified version of the Time Marching Algorithm (TMA) allows to probe and analyze the behavior of the different double dynamic networks, in particular, the effects of the type and amount of crosslinks on their linear viscoelastic spectra. To this end, the dynamics of the double networks are compared with the respective individual responses of the polymeric component without crosslinks and the single networks (possessing only physical or only chemical crosslinks), in order to quantify their contributions to the relaxation mechanisms, particularly the interplay between disentanglement and bond association/dissociation processes. With the help of the TMA model, we also examine the respective roles of the lifetime of stickers, polydispersity, and molar mass. Triggered by the good comparison between predictions and experimental data, we propose a framework to tune material parameters in order to obtain a desired viscoelastic behavior.

Precise control of thermal deprotection behavior and dismantlable adhesion property of the acrylate copolymers containing BOC-protected hydroxy group

The acrylate copolymers consisting of 4-hydroxybutyl acrylate (HBA), 2-(tert-butoxy-carbonyloxy)ethyl acrylate (BHEA) or 4-(tert-butoxycarbonyloxy)butyl acrylate (BHBA), and 2-ethylhexyl acrylate (2EHA) as the repeating units were synthesized by radical copolymerization. The performance as the pressure-sensitive adhesives (PSAs) used for a dismantlable adhesion system was investigated. The glass transition temperatures and the adhesive properties were precisely controlled by the comonomer composition of the copolymers. It was confirmed that the deprotection of the tert-butoxycarbonyl (BOC) group rapidly proceeded for the BOC-containing acrylate copolymers as the PSAs. It resulted in the decrease of the adhesion strength during a debonding process by heating. The thermal stability during use and the quick response for on-demand debonding were simultaneously achieved by the use of alkyl p-toluenesulfonates as the thermally latent acids (TLAs).

Natural rubber-based pressure sensitive adhesive as a drug carrier

Natural rubber (NR) has been utilized in several products from its interesting unique properties. This study aimed to develop the pressure-sensitive adhesives (PSA) as the transdermal patches from NR by two-roll mill kneading technique. Hydroxyethyl cellulose (HEC) was blended as a tackifier agent. The propranolol HCl and ibuprofen at different parts per hundred of rubber (phr) were loaded into this developed PSA. The appearance, thickness, crystallinity, contact angle, water sorption and erosion, adhesion, and in vitro drug permeation of these patches were evaluated. The thickness of all patches was in the range of 0.46–1.07 mm. The drug-loaded patches showed diverse unique topographies depended on both type and amount of drug incorporation. From powder X-ray diffraction analysis, the plain NR-PSA showed the amorphous structure, while the halo pattern inserted with sharp drug peaks were observed on drug-loaded PSA. The contact angle of all samples was in the range of 80–90° indicating their hydrophobic surface. However, they displayed an increased % water sorption with the time of soaking. The 2–4 N adhesion force was evident for all fabricated drug-loaded PSAs. The propranolol HCl permeated from PSA notably lower than ibuprofen. The residual of the drugs in patches was about 85–90 %. These results provided the basic physicochemical properties for the further development of PSA as the transdermal patch.[copyright information to be updated in production process]

Influence of Nanoclay on the Thermo-Mechanical Properties of Silicone Pressure-Sensitive Adhesives.

This research was carried on newly obtained innovative materials-self-adhesive one-sided tapes based on silicone pressure-sensitive adhesives. In order to obtain tapes, the stable adhesive composition was subjected to physical modification by incorporating into it various amounts of selected silicon fillers. The produced pressure-sensitive adhesives were tested for viscosity and thermogravimetric analysis, as well as the manufactured tapes; i.e., peel adhesion, tack, cohesion at room and elevated temperature, SAFT test (shear adhesive failure temperature), and shrinkage. The prepared self-adhesive tapes retained their self-adhesive properties at a level close to the initial level while increasing the thermal resistance by 70-75 °C, reaching the level of 220-225 °C. The new self-adhesive materials have application potential and can be used as a material for special applications in the field of electrical engineering and heavy industry.

Formulation and Evaluation of a Drug-in-Adhesive Patch for Transdermal Delivery of Colchicine.

Gout is one of the most prevalent rheumatic diseases, globally. Colchicine (COL) is the first-line drug used for the treatment of acute gout. However, the oral administration of COL is restricted, owing to serious adverse reactions. Therefore, this study aimed to develop a drug-in-adhesive (DIA) patch to achieve transdermal delivery of COL. We investigated the solubility of COL in different pressure-sensitive adhesives (PSAs) using slide crystallization studies. The COL-DIA patches were optimized based on in vitro skin penetration studies and evaluated by in vivo pharmacokinetics and pharmacodynamics. The results showed that the optimized COL-DIA patch contained 10% COL, Duro-Tak 87-2516 as PSA, 5% oleic acid (OA) and 5% propylene glycol (PG) as permeation enhancer, exhibiting the highest in vitro cumulative penetration amount of COL (235.14 ± 14.47 μg∙cm−2 over 48 h). Pharmacokinetic studies demonstrated that the maximum plasma drug concentration (Cmax) was 2.65 ± 0.26 ng/L and the mean retention time (MRT) was 37.47 ± 7.64 h of the COL-DIA patch, effectively reducing the drug side effects and prolonging drug activity. In addition, pharmacodynamic studies showed the patch significantly decreased the expression levels of inflammatory factors of gouty rats and reduced pathological damage in the ankle joint of rats, making it an attractive alternative to the administration of COL for the treatment of gout.

Development and evaluation of a drug-in-adhesive transdermal delivery system for delivery of olanzapine

ABSTRACT Objectives Olanzapine (OZP) is a safe and effective atypical antipsychotic drug used in treating schizophrenia and bipolar disorders. The dosage forms currently on the market for OZP are administered via oral or intramuscular routes. However, there are many problems associated with oral and intramuscular routes of drug administration. Thus, our aim was to develop a drug-in-adhesive transdermal delivery system (TDS) that can deliver OZP for 3 days. Methods We determined passive permeation, effect of oleic acid as chemical enhancer, and delivery of OZP across different skin types. Based on preliminary studies and saturation solubility of OZP in different pressure-sensitive adhesives (PSAs), we formulated and characterized solution-based TDS in acrylate PSA and suspension-based TDS in silicone and PIB PSA, with oleic acid as chemical enhancer. Results Acrylate solution-based TDS, silicone, and PIB suspension-based TDS delivered 58.97 ± 6.59 µg/sq.cm, 129.34 ± 16.59 µg/sq.cm, and 245.00 ± 2.51 µg/sq.cm, respectively, using in vitro permeation testing. PIB PSA suspension-based TDS met the 3 days desired target delivery. Skin irritation testing using In vitro EpiDermTM skin irritation test (EPI-200-SIT) kit found PIB TDS to be nonirritant. Conclusion The PIB PSA suspension-based TDS could serve as a potentially effective transdermal delivery system for olanzapine.

Hot-Melt and Pressure-Sensitive Adhesives Based on Styrene-Isoprene-Styrene Triblock Copolymer, Asphaltene/Resin Blend and Naphthenic Oil.

Asphaltene/resin blend (ARB) extracted from heavy crude oil was used to modify poly(styrene-block-isoprene-block-styrene) (SIS) to make it an adhesive. There were prepared double and triple mixtures containing 10–60% SIS, 10–40% ARB, and 10–50% naphthenic oil used as an additional plasticizer. The viscoelasticity of the mixtures at 25 °C and 120 °C was studied, their flow curves were obtained, and the temperature dependences of the loss tangent and the components of the complex modulus were measured. In addition, the mixtures were used as hot-melt adhesives (HMAs) and pressure-sensitive adhesives (PSAs) in the shear, peel, and pull-off tests of the adhesive bonds that they formed with steel. Both naphthenic oil and ARB act as plasticizers for SIS and make it sticky. However, only the combined use of ARB and the oil allows for achieving the best set of adhesive properties of the SIS-based mixture. High-quality HMA requires low oil content (optimal SIS/ARB/oil ratio is 50/40/10, pull-off adhesion strength (τt) of 1990 kPa), whereas a lot of the oil is needed to give SIS characteristics of a PSA (SIS/ARB/oil is 20/40/40, τt of 100 kPa). At the same time, the resulting PSA can be used as a hot-melt pressure-sensitive adhesive (HMPSA) that has many times lower viscosity than HMA (13.9 Pa·s versus 2640 Pa·s at 120 °C and 1 s−1) but provides a less strong adhesive bond (τt of 960 kPa).

The determination of fractal dimensions of blast-cleaned steel substrates by means of comparative cross-section image analysis and contact stylus instrument measurements

Morphological parameters of substrate surfaces determine the adhesion of coatings and pressure-sensitive adhesives. This paper is concerned with the assessment of fractal parameters by means of cross-section images and contact stylus instrument measurements of blast-cleaned substrates. Mild steel samples were prepared with different abrasive materials. Images were taken from a total of 12 surface configurations with an optical microscope. From each of the cross-section, a 2D profile of the steel surface was derived using the ImageJ image manipulation software. The fractal dimensions of these profiles were estimated by means of the box-counting method and then compared fractal values for 2D profiles taken from contact stylus measurements. Design of Experiment (DoE) was applied to statistically analyze the relationships. The factors considered included abrasive type, surface preparation grade, surface roughness, and most importantly for this paper, the surface profile evaluation method. The profile evaluation methods included cross-section analysis and contact stylus instrument measurements. Regardless of the method used to determine the surface profile, identical relative trends resulted for both measurement variants, with normalised values approximately twice as high for the cross-section profiles compared to the ones from contact stylus data.

Mechanistic Study of Release Characteristics of Two Active Ingredients in Transdermal Patch Containing Lidocaine-Flurbiprofen Ionic Liquid.

Ionic liquids (ILs) have been proven to be an efficient technology for enhancing drug skin permeability. However, the question of whether the two components of ILs are released synchronously in transdermal preparations has remained unclear. Thus, this study aimed to investigate the release characteristics of two components of ILs and their underlying molecular mechanism. The ILs containing flurbiprofen (FLU) and lidocaine (LID) were synthesized and characterized. The four typical acrylates pressure sensitive adhesives (PSAs) with different functional groups were synthesized and characterized. The effects of PSAs on the release characteristics of two components of ILs were investigated by drug release tests and verified by skin permeation experiments. The action mechanisms were revealed by FTIR, Raman, dielectric spectrum, and molecular docking. The results showed that the average release amount of FLU (0.29 μmol/cm2) and LID (0.11 μmol/cm2) of ILs in the four PSAs was significantly different (p < 0.05), which illustrated that the two components did not release synchronously. The PSA−none and PSA−OH with low permittivity (7.37, 9.82) interacted with drugs mainly by dipole-dipole interactions and hydrogen bonds. The PSA−COOH and PSA−CONH2 with high permittivity (11.19, 15.32) interacted with drugs mainly by ionic bonds and ionic hydrogen bonds. Thus, this study provides scientific guidance for the application of ILs in transdermal preparations.

How Particle Deformability Influences the Surfactant Distribution in Colloidal Polymer Films.

The distribution of surfactants in waterborne colloidal polymer films is of significant interest for scientific understanding and defining surface properties in applications including pressure-sensitive adhesives and coatings. Because of negative effects on appearance, wetting, and adhesion, it is desirable to prevent surfactant accumulation at film surfaces. The effect of particle deformation on surfactant migration during film formation was previously investigated by Gromer et al. through simulations, but experimental investigations are lacking. Here, we study deuterium-labeled sodium dodecyl sulfate surfactant in a poly(butyl acrylate) latex model system. The particle deformability was varied via cross-linking of the intraparticle polymer chains by differing extents. The cross-linker concentration varied from 0 to 35 mol % in the copolymer, leading to a transition from viscoelastic to elastic. Ion beam analysis was used to probe the dry films and provide information on the near-surface depth distribution of surfactant. Films of nondeformable particles, containing the highest concentration of cross-linker, show no surfactant accumulation at the top surface. Films from particles partially deformed by capillary action show a distinct surfactant surface layer (ca. 150 nm thick). Films of coalesced particles, containing little or no cross-linker, show a very small amount of surfactant on the surface (ca. 20 nm thick). The observed results are explained by considering the effect of cross-linking on rubber elasticity and applying the viscous particle deformation model by Gromer et al. to elastically deformed particles. We find that partially deformed particles allow surfactant transport to the surface during film formation, whereas there is far less transport when skin formation acts as a barrier. With elastic particles, the surfactant is carried in the water phase as it falls beneath the surface of packed particles. The ability to exert control over surfactant distribution in waterborne colloidal films will aid in the design of new high-performance adhesives and coatings.

Implications of styrenic triblock copolymer gel mechanics on midblock bridging fraction

Triblock copolymer gels have garnered considerable scientific interest over the past few decades and are used in a variety of applications including consumer cushioning, pressure-sensitive adhesives, and ballistics gels. While many of their applications rely upon understanding mechanical properties, mechanical studies of block copolymer gels are relatively disjointed with each focusing on specific copolymers, which inherently have a fixed molecular weight and composition. The present study examines the quasistatic mechanical response of styrenic triblock copolymer gels composed of seven unique triblock copolymers at various concentrations. Resultant stress-extension data is fitted with the slip-tube network (STN) theory that describes gel mechanics based upon crosslinked network (Gc) and chain entanglement (Ge) modulus contributions. Collectively, modulus contributions imply that midblock bridging is independent of copolymer identity (i.e., molecular weight and block fraction) and dependent on triblock copolymer concentration via Fb ∝ φABA0.91±0.39 over the concentration range examined (φABA = 0.05–0.39). Gels composed of a complementary diblock-triblock copolymer pair were subsequently analyzed to explore the influence of interlocking loop-loop and loop-bridge pairs within the effective midblock bridging population. These results point to the presence of a physically significant quantity of interlocked loops, but quantitative analysis was inconclusive.

Topologically designed cross-linking network for stretchable and recoverable pressure-sensitive adhesives with exceptional softness

There is an increasing demand for soft-electronic devices. Such devices require adhesives that demonstrate appropriate stretching and recovery to support the assembly of various parts. The adhesives need to avoid plastic deformation and adhesion failure under repeated stretching. However, stretchable adhesives with covalent cross-linked polymer network and inorganic fillers have limitations in softness and adhesion performance, which is due to the hinder of chain mobility. Thus, providing elasticity without the compensation of chain mobility is strongly required. In this study, we introduced slide-blocking units to movable cross-linked polymers to improve the elasticity. The topologically designed cross-linking network causes a strain stiffening effect in the adhesives, showing outstanding softness, adhesion performance, and mechanical properties. Furthermore, the adhesives with the unique cross-linking network exhibited excellent stretching and recovery properties.

Research advances in vegetable-oil-based pressure-sensitive adhesives

Pressure-sensitive adhesive (PSA) is a kind of viscoelastic material with the viscous properties of liquids and the elastic properties of solids that can adhere to the surfaces of various substrates only under light pressure without phase change. PSAs derived from petroleum-based materials are generally non-biodegradable and disposable; therefore, a large amount of waste is generated from PSA products. Preparation of PSAs using renewable vegetable oil as raw material is an effective way to reduce dependence on petrochemical resources and environmental pollution. This paper summarizes the recent progress on vegetable-oil-based PSAs. Vegetable-oil-based PSAs mainly include epoxy resin, acrylic resin, fatty acid derivatives, polyester and polyurethane according to the chemical structures of vegetable-oil-based polymers. The design ideas and modification methods of vegetable-oil-based PSAs are introduced, including the development of functional vegetable oil monomers and the optimization of the polymer structure, so as to provide theory and reference for the design and development of new bio-based PSAs.

Adhesion Improvement of Solvent-Free Pressure-Sensitive Adhesives by Semi-IPN Using Polyurethanes and Acrylic Polymers.

To improve the peel strength and holding time of polypropylene glycol (PPG)-based pressure-sensitive adhesives (PSAs), a semi-interpenetrating polymer network (semi-IPN) was prepared using acrylic polymers. In addition, to prevent air pollution due to volatile organic compound emissions and avoid the degradation of physical properties due to a residual solvent, the PPG-based semi-IPN PSAs were fabricated by an eco-friendly solvent-free method using an acrylic monomer instead of an organic solvent. PPG-based semi-IPN PSAs with different hard segment contents (2.9–17.2%) were synthesized; their holding time was found to depend on the hard segment contents. The peel strength was improved because of the formation of the semi-IPN structure. Moreover, the high degree of hard domain formation in the semi-IPN PSA, derived from the increase in the hard segment content using a chain extender, resulted in a holding time improvement. We believe that the as-prepared PSAs can be used in various applications that require high creep resistance.

A pressure-sensitive adhesive made from macca carbon for medical use

Macca carbon (MC), derived from high-temperature carbonized macadamia nut-in-shell wastes from macadamia nut processing, exhibits a high surface area, high number of electrons, and high efficiency in emitting far-infrared (FIR) radiation at wavelengths between 4 and 20 μm. Numerous inventions have demonstrated promising results in health improvement applications, such as increased blood circulation, less inflammation, and enhanced life expectancy. In this study, MC and a pressure-sensitive adhesive (PSA) were coupled to form a new bandage called an MC cohesive bandage. It was manufactured by combining various quantities of MC powder with PSA and applying it to a spandex fabric tape. The peeling test, water permeability, and skin irritation were examined. The quantity of FIR radiation between 6 and 14 μm and the thermal properties of MC cohesive bandages were investigated. The FIR penetration effectiveness was determined by measuring the temperature rises from the streaky pig skin covered with MC cohesive bandages at various depths.

Adjusting the stickiness of concentrated pea protein – apple pectin systems via the biopolymer mixing ratio

Stickiness is the combination of adhesion and cohesion and key characteristic for binders in foods to combine particulates into a coherent mass. We investigated the influence of mixing ratio of pea protein and apple pectin powders (w/w) at pH 6 on stickiness by assessing textural, rheological, and binding properties of a concentrated suspension (25 wt% powder concentration). The elastic but soft texture of a pea protein suspension alone showed cohesive failure with low stickiness in line with limited viscous properties. A pectin suspension also showed low stickiness, but with an adhesive failure, which was due to the hard and stiff nature of the matrix preventing sufficient adhesive interactions. However, mixtures of pea proteins and apple pectin with multiphase morphologies displayed a balanced combination of viscous and elastic properties, which was beneficial for stickiness. In particular, the mixture with 67% pea proteins and 33% apple pectin showed a distinct frequency dependence in their rheological moduli. Viscous properties dominated at low frequencies improving bond formation (adhesion), while elastic properties became more important at high frequencies opposing stress acting against the bond (cohesion). This study highlights the importance of a characteristic viscoelasticity for stickiness of pressure-sensitive adhesives and how it can be tailored through biopolymer mixing.

Thermally stable and soft pressure-sensitive adhesive for foldable electronics

Soft pressure-sensitive adhesives (PSAs) are widely adopted in foldable electronics to integrate devices and to form multiple neutral planes (MNPs), that protect brittle films in the devices during folding. The mechanical properties and reliability of PSAs at the operating temperature of foldable devices are key factors for their practical application. Herein, we synthesize a thermally stable, yet soft PSA via initiated chemical vapor deposition (iCVD). The molecular network of the soft PSA is composed of a copolymer film of 2-ethylhexyl acrylate (EHA) and 2-hydroxyethylacrylate (HEA) monomers, whose composition is controlled systematically by tuning the input flow rate of each monomer during iCVD. As a result, the storage modulus of the synthesized PSA is lower than 1 MPa from −35 to 85 ℃ without any flow. The hard-coated laminate integrated by the synthesized PSA can be protected during bending at −35 ℃ by the MNPs, as the inserted PSA is still soft at such a low temperature. Moreover, the shear strength of the synthesized PSA does not degrade even after exposure to temperatures of −40 ℃ and 85℃ for 7 days. The extraordinary mechanical reliability and the durability against delamination is further confirmed through a folding fatigue test and a static folding test (holding fold state) under various operating temperatures (-40 ℃, 25 ℃, and 85 ℃).

Fe(III)-coordinated N-[tris(hydroxymethyl)methyl]acrylamide-modified acrylic pressure-sensitive adhesives with enhanced adhesion and cohesion for efficient transdermal application

Pressure-sensitive adhesives are critical to the product's safety, efficacy, and quality in transdermal drug delivery systems. However, many defects of transdermal patches (e.g., insufficient adhesion, patch displacement, and “dark ring” phenomenon) remain. Herein, the N-[tris(hydroxymethyl)methyl]acrylamide (NAT)-modified acrylic pressure-sensitive adhesive coordinated with Fe(III) (AA-NAT/Fe3+) was creatively proposed. Results demonstrated that the adhesiveness and cohesiveness of the optimized AA-NAT/Fe3+ were higher by 1.8- and 9.7-fold, respectively, than those of commercially available DURO-TAK® 87-4098 due to the hydrogen bonding interaction of NAT-skin interface and coordination of NAT-Fe3+. Moreover, compared with that of DURO-TAK® 87-4098, the adhesion time of AA-NAT/Fe3+ on the human forearm was remarkably prolonged, and no “dark ring” phenomenon was observed for AA-NAT/Fe3+ after removal. After clonidine (CLO) was loaded into AA-NAT/Fe3+, controlled drug release and a drug transdermal behavior were endowed for CLO@AA-NAT/Fe3+in vitro and in vivo. AA-NAT/Fe3+ still maintained superiority in adhesion and cohesion properties after CLO loading. These observations would contribute to the development of pressure-sensitive adhesives with outstanding adhesion and cohesion for transdermal patches. Statement of significanceThis N-[tris(hydroxymethyl)methyl]acrylamide-modified acrylic pressure-sensitive adhesive coordinated with Fe(III) has enhanced adhesion and cohesion properties, which provide a simple but effective strategy to solve the problems (e.g., insufficient adhesion, patch displacement, and “dark ring” phenomenon) in existing transdermal patches.

A rate-dependent cohesive zone model for adhesive damage considering fibrillation

The pressure-sensitive adhesive (PSA) has been widely utilized in engineering and biomedicine fields. It is known the fibrillation process of PSA can considerably increase the adhesive energy, which significantly affects its adhesive behavior. Since the classical bilinear cohesive zone model (CZM) did not account for the fibril evolution, this paper aims to propose a rate-dependent CZM based on the physical mechanism of fibrillation to describe the cohesive failure of PSA. The multilinear traction-separation law (TSL) was established accordingly, including homogeneous deformation, cavity nucleation and dilatation, and fibril evolution. After being implemented into the FE software using a user-subroutine UMAT, the proposed CZM was validated by experimental data from probe-tack tests and then was utilized to investigate the effect of loading rate on PSA's adhesive performance of the peeling test. By examining the fibril's strain rate distribution using the proposed CZM, it is possible to correlate the PSA's adhesive performance under 90° peeling tests and the probe-tack test, thereby compensating for the theoretical prediction's inaccuracy due to the assumption of constant strain rate. It demonstrates the proposed CZM is a promising approach to investigating the rate-dependent cohesive failure of PSA considering fibrillation.