Pressure-sensitive Adhesive Films Research Articles

The Effect of Cellulose Nanocrystal Reassembly on Latex-Based Pressure-Sensitive Adhesive Performance.

Different cellulose nanocrystal (CNC) forms (dried vs never-dried) can lead to different degrees of CNC reassembly, the formation of nanofibril-like structures, in nanocomposite latex-based pressure-sensitive adhesive (PSA) formulations. CNC reassembly is also affected by CNC sonication and loading as well as the protocol used for CNC addition to the polymerization. In this study, carboxylated CNCs (cCNCs) were incorporated into a seeded, semibatch, 2-ethylhexyl acrylate/methyl methacrylate/styrene emulsion polymerization and cast as pressure-sensitive adhesive (PSA) films. The addition of CNCs led to a simultaneous increase in tack strength, peel strength, and shear adhesion, avoiding the typical trade-off between the adhesive and cohesive strength. Increased CNC reassembly resulted from the use of dried, redispersed, and sonicated cCNCs, along with increased cCNC loading and addition of the cCNCs at the seed stage of the polymerization. The increased degree of CNC reassembly was shown to significantly increase the shear adhesion by enhancing the elastic modulus of the PSA films.

Adhesion and Contact Aging of Acrylic Pressure-Sensitive Adhesives to Swollen Elastomers.

Fluid-infused (or swollen) elastomers are known for their antiadhesive properties. The presence of excess fluid at their surface is the main contributor to limiting contact formation and minimizing adhesion. Despite their potential, the mechanisms for adhesion and contact aging to fluid-infused elastomers are poorly understood beyond contact with a few materials (ice, biofilms, glass). This study reports on adhesion to a model fluid-infused elastomer, poly(dimethylsiloxane) (PDMS), swollen with silicone oil. The effects of oil saturation, contact time, and the opposing surface are investigated. Specifically, adhesion to two different adherents with comparable surface energies but drastically different mechanical properties is investigated: a glass surface and a soft viscoelastic acrylic pressure-sensitive adhesive film (PSA, modulus ∼25 kPa). Adhesion between the PSA and swollen PDMS [with 23% (w/w) silicone oil] retains up to 60% of its value compared to contact with unswollen (dry) PDMS. In contrast, adhesion to glass nearly vanishes in contact with the same swollen elastomer. Adhesion to the PSA also displays stronger contact aging than adhesion to glass. Contact aging with the PSA is comparable for dry and unsaturated PDMS. Moreover, load relaxation when the PSA is in contact with the PDMS does not correlate with contact aging for contact with the dry or unsaturated elastomer, suggesting that contact aging is likely caused by chain interpenetration and polymer reorganization within the contact region. Closer to full saturation of the PDMS with oil, adhesion to the PSA decreases significantly and shows a delay in the onset of contact aging that is weakly correlated to the poroelastic relaxation of the elastomer. Additional confocal imaging suggests that the presence of a layer of fluid trapped at the interface between the two solids could explain the delayed (and limited) contact aging to the oil-saturated PDMS.

Liquid and Pressure-Sensitive Adhesives Based on Cassava Starch and Gelatin Capsule Residue: Green Alternatives for the Packaging Industry

Natural polymer-based adhesives are green alternatives, necessary to reduce the problems impacted by synthetic adhesives. Starch and gelatin have extraordinary potential for the synthesis of biobased adhesives. Citric acid (CA), a natural acid, induces the crosslinking and hydrolyzing of both gelatin and starch. In this sense, this work deals with the use of gelatin capsule residues as a promising material to produce biobased adhesives in combination with cassava starch in the presence of different CA concentrations characterizing their mechanical, physicochemical and microstructural properties. Depending on CA concentration, formulations adjusted to different applications can be obtained such as liquid and pressure-sensitive adhesive films. The inclusion of CA allows us not only to improve the applicability of the system since it modifies the flowability of the adhesives as evidenced by the observed changes in the viscosity (from 158.3 to 90.3 for formulations with 20 and 80% CA, respectively). In addition, mechanical profiles showed that the inclusion of CA increased the adhesive bond strength (from 2230.7 to 2638.7 for formulations with 20 and 80% CA, respectively). Structural modifications induced by CA in adhesive formulations were highlighted by ATR-FTIR analysis.

Fabrication and peeling behavior of thermally conductive pressure-sensitive adhesive films with embedded graphite composite patterns

Thermal interface materials (TIMs) have been widely employed to address the thermal issues arising in electronics. Given that heat generated at heat sources is dissipated into heat sinks through TIMs, the softer they are, the more efficient the heat transfer is. In this paper, a thermally conductive pressure-sensitive adhesive (PSA) film (gr-PSA film) in which graphite composite patterns were embedded was fabricated and its thermal conductivity and peeling behavior were investigated. Because of its low storage modulus (2.4 × 104 Pa), a mixture of soft polyurethane acrylate, butyl acrylate, and 2-ethylhexyl acrylate was used to fabricate a PSA. The in-plane and through-plane thermal conductivity of the gr-PSA film were measured as 1.56 (±0.37) Wm−1K−1 and 0.25 (±0.03) Wm−1K−1, respectively. The peeling behavior of the gr-PSA tape was investigated by a 90° peel test and the results were compared with simulation results obtained by cohesive zone modeling implemented in the finite element method. Both results show that the peel force oscillated when the gr-PSA tape was peeled. Because the gr-PSA tape comprises alternating stiff and compliant segments, more force is needed peeling when bending the stiff segments.

Effect of drying conditions on adhesion strength of a pressure-sensitive adhesive

ABSTRACT Regular surface roughness could be created on the surface of a pressure-sensitive adhesive (PSA) film through Marangoni flow during the drying process. Therefore, tailoring of both surface and bulk characteristics of the PSA and consequently its adhesion strength could be expected by controlling the drying conditions. Herein, surface and bulk properties of a water-based PSA dried at various temperatures and humidities were scrutinized. Increase in the drying temperature improved the adhesion strength of the PSA to poly(ethylene terephthalate) due to enhanced surface nanoroughness of its film. At constant humidity, the higher the Péclet number, the higher the Marangoni number and the rougher the PSA film surface. Drying humidity rise, however, improved the adhesion strength due to more uniform distribution of copolymers constituting the PSA, better interdiffusion of chains through the interface of polymer particles in a prolonged drying process, and increased surface free energy of the film. The adhesion strength of the PSA, similar to the here-defined viscoelastic dissipation ability, demonstrated a power dependence on the film surface nanoroughness. This newly-defined parameter considers taking advantage of the real viscoelastic dissipation of the PSA regarding its potentiality through thorough wetting of the substrate surface with the PSA.

Variation in adhesion properties and film morphologies of waterborne pressure‐sensitive adhesives containing an acid‐rich diblock copolymer additive

AbstractOne challenge for waterborne pressure‐sensitive adhesives (PSA)s is the typical tradeoff between cohesion and adhesion. Others have shown that waterborne PSA films with thin, hard boundaries formed from short poly(acid) segments surrounding soft particles can have simultaneous improvements in adhesion and cohesion. To study this approach in commercial‐type acrylic waterborne PSAs, a diblock copolymer (BCP) composed of poly(acrylic acid)‐block‐(n‐butyl acrylate) (PAA‐b‐PBA) is added at 1–5 wt% to PSAs composed of 100% PBA (PSA (0% acid)) or 99% BA/1% AA (PSA (1% acid)). Films of these blends prepared using industrially relevant conditions reveal complex nanodomains in atomic force microscopy (AFM) images. PSA performance tests showed that 1–2 wt% BCP additive nearly tripled adhesion to stainless steel for PSA (0% acid) while improving cohesion. Nonetheless, AFM images of PSA (0% acid) with 1–2 wt% BCP display ill‐defined morphologies, with clear percolated structures apparent primarily in films with 5% BCP. This indicates that film morphologies which enhance adhesion may not correlate with AFM features. Moreover, the balance of adhesion and cohesion of PSA (1% acid) without BCP exceeds that of any of the BCP blends, demonstrating the challenge of using designed microstructures to improve upon conventional PSAs containing copolymerized acids.

Macromol. React. Eng. 3/2022

Macromolecular Reaction EngineeringVolume 16, Issue 3 2270005 Cover PictureFree Access Macromol. React. Eng. 3/2022 First published: 16 June 2022 https://doi.org/10.1002/mren.202270005AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract Front Cover: Carboxylated cellulose nanocrystals (cCNCs) are used to enhance latex-based pressure-sensitive adhesive (PSA) properties. AFM imaging reveals that cCNCs interact with latex particles and each other; thus, omitting ultrasonication at the preparation stage preserves these interactions and leads to greater property enhancements. The research demonstrates how cCNCs provide superior, fibril-like reinforcements to PSA films without the technical challenges associated with producing composites with nanofibrils. This is reported by Marc A. Dubé and co-workers in article number 2100051. Volume16, Issue3Special Issue: Green Macromolecular Reaction EngineeringJune 20222270005 RelatedInformation

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.

Graphene as effective anti-fading agent for the protection of artworks

Since all art materials in time are prone to degradation due to environmental conditions, a solution is needed to delay or even to prevent such an interference. Graphene, the pioneer of 2D materials, seems to pave the way to this end either as a protective layer on artworks or as an inclusion in paints, dyes, pigments acting as protective additive, respectively. Regarding the former, the proposed invention provides a method for applying a protective graphene coating onto a surface, such a two- or three-dimensional artwork or other coloured surface. The steps followed within this method are: Deposition of Chemical Vapor Deposition (CVD) produced graphene onto a supporting substrate in order to produce a graphene/substrate composite; Removal the graphene membrane from the supporting substrate; and Deposition the graphene membrane onto the surface of interest All the pre-mentioned steps are performed following the roll-to-roll method (Choi et al., 2015), with the assistance of a tailor-made laminator. However, the direct deposition of graphene onto artworks may not be straightforward due to the wet transfer and hot lamination conditions that can be catastrophic for fragile painted substrates. The novel strategy designed exploits the high-quality CVD monolayer graphene and uses a pressure-sensitive adhesive film (PSAF) in the transfer process that has been demonstrated to enable graphene wetting on the final target-substrate (Kim et al., 2015), thus maximizing the contact area and van der Waals interactions. The low work of adhesion between graphene and the PSAF, compared to the corresponding between graphene and the destination surface, promotes the transfer that can be performed at mild pressure and temperature conditions, without using a surface modifier or adhesives (Martins et al. 2013). Additionally, the proposed roll-to-roll method does not affect the mechanical integrity of the typical paper substrates used in graphic arts. As for the protective additive case, graphene is employed in the form of an aqueous dispersion in media such as paints, dyes, inks, pigments and/or varnishes used for artistic purposes in order to create indelible colours to capable to prevent degradation, attributed to UV radiation, moisture and oxidizing agents. The method presents a new approach for obtaining aqueous dispersions for the hydrophobic graphene and thus, protecting artworks and painted indoor/outdoor wall surfaces taking advantage of the optical and barrier properties of graphene.

Incorporation of Polymer-Grafted Cellulose Nanocrystals into Latex-Based Pressure-Sensitive Adhesives.

While the improvement of water-based adhesives with renewable additives is important as industry shifts toward more sustainable practices, a complete understanding of how the compatibility between additives and polymers affects adhesive performance is currently lacking. To elucidate these links, cellulose nanocrystals (CNCs) were first functionalized via surface-initiated atom-transfer radical polymerization with the hydrophobic polymers poly(butyl acrylate) (PBA) and poly(methyl methacrylate) (PMMA) to facilitate their incorporation into latex-based pressure-sensitive adhesives (PSAs). Next, PBA latexes were synthesized using seeded semibatch emulsion polymerization with unmodified or polymer-grafted CNCs added in situ at a loading of 0.5 or 1 phm (parts per hundred parts of monomer). Viscosity and electron microscopy suggested that the polymer-grafted CNCs were incorporated inside or on the latex particles. PSAs containing any CNC type had one or more improved properties (compared to the no-CNC "base case"); CNCs with a low degree of polymerization (DP) grafts exhibited improved tack (up to 2.5-fold higher) and peel strength (up to 6-fold higher) relative to PSAs with unmodified CNCs. The best performing PSA contained the low DP PMMA-grafted CNCs, which is attributed to the higher glass transition temperature and the higher wettability of the PMMA grafts compared to PBA, and the more uniform dispersion of polymer-grafted CNCs throughout the PSA film. In contrast, PSAs containing CNCs with high DP grafts resulted in reduced tack and peel strength (compared to low DP grafts) due to enhanced CNC aggregation. Unfortunately, all PSAs containing polymer-grafted CNCs exhibited inferior shear strength relative to PSAs with unmodified CNCs (and comparable shear strength to the no-CNC "base case"). Collectively, these results provide guidelines for future optimization of more sustainable latex-based PSAs.

Study of UV-initiated polymerization and UV crosslinking of acrylic monomers mixture for the production of solvent-free pressure-sensitive adhesive films

UV-polymerizable and UV-crosslinkable pressure-sensitive adhesive acrylic compositions are widely applied for high-quality carrier-free films, one-sided or double-sided self-adhesive tapes. Comprehensive studies of the properties of novel acrylic PSAs for carrier-free films or adhesive tapes were carried out. Solvent-free acrylic pressure-sensitive adhesive layers were UV-crosslinked using various photoreactive crosslinking agents. Polymer content during UV-polymerization, prepolymers viscosity, temperature changes of prepolymer during UV-initiated polymerization process were investigated. The chemical structure of prepolymer and polymerized acrylic film were examined using FTIR spectroscopy. Prepolymer mixtures were transferred on the transparent carriers to form 1 mm thick polymer films, and then UV-crosslinked after the addition of the selected acrylic crosslinker. Final adhesive films were then tested to evaluate their functional properties as the tack, peel adhesion, and shear strength at 20 °C and 70 °C. From the results reveal that both concentrations of acrylic acid in the prepolymer, and cross-linking agent in the final polymer layer, have a significant influence on the functional properties of the produced PSA films.

High-Resolution and Facile Patterning of Silver Nanowire Electrodes by Solvent-Free Photolithographic Technique Using UV-Curable Pressure Sensitive Adhesive Film.

Patterning of silver nanowires (AgNWs) used in fabricating flexible and transparent electrodes (FTEs) is essential for constructing a variety of optoelectronic devices. However, patterning AgNW electrodes using a simple, inexpensive, high-resolution, designable, and scalable process remains a challenge. Therefore, herein a novel solvent-free photolithographic technique using a UV-curable pressure sensitive adhesive (PSA) film for patterning AgNWs is introduced. The UV-curable PSA film can be selectively patterned by photopolymerization under UV exposure through a photomask. The AgNWs embedded in the non-photocured adhesive areas of the film are firmly held by a crosslinked network of photocurable resin when the patterned film is attached to the AgNW-coated substrate and additionally irradiated by UV light. After peeling off the film, the positive pattern of AgNW electrodes remains on the substrate, while the negative pattern is transferred to the film. This solvent-free photolithographic technique, which does not use toxic solvents, provides superior pattern features, such as fine line widths and spacings, sharp line edges, and low roughness. Therefore, the developed technique could be successfully applied in the development of flexible and transparent optoelectronic devices, such as a self-cleaning electro-wetting-on-dielectric (EWOD) devices, transparent heaters, and FTEs.

Preparation and characterization of polyacrylate emulsion pressure-sensitive adhesives with various lengths of fluorinated side chains

A series of fluorinated polyacrylate emulsion pressure-sensitive adhesives (PSA) with various lengths fluorinated side chains were synthesized by using n-butyl acrylate (nBA), acrylic acid (AA), 2-hydroxyethyl acrylate (HEA) together with three kinds of fluorine monomers trifluoroethyl methacrylate (TFEMA), hexafluorobutyl methacrylate (HFBMA) and dodecafluoroheptyl methacrylate (DFHMA). The influences of fluorocarbon chains’ length on the particle size of the latex, as well as on thermostability (DSC, TG) and surface properties (XPS, CA, AFM) of the PSA films were investigated. The results showed that T g and thermal stability of the PSA were both increased with the introduction of F-monomers with various lengths of fluorinated side chains, and the shorter the side chain, the more the T g and thermal stability increased. The XPS results indicated that the surface atom percentage of F element of film increased with the escalation of the length of fluorocarbon lateral chain, which results in the water contact angle and surface roughness increment of the PSA films. Finally, effects of fluorocarbon chains’ length on the adhesive properties (i.e. loop tack, peel strength and shear strength) of the fluorinated latex PSA were also evaluated.

Relationship between large amplitude oscillatory shear (LAOS) experiments and commercial pressure sensitive adhesives applications testing

Abstract Historically, analytical test methods on pressure sensitive adhesives (PSAs) have shown modest correlation to applications test results. Since applications tests such as peel strength and shear strength involve large deformations of the adhesive, large amplitude oscillatory shear (LAOS) experiments may correlate more strongly to the applications test results than typical linear viscoelastic measurements. Here we report some of the earliest LAOS measurements on commercial PSA films and compare them to the measured peel strength and shear strength. The parameters, G’M, Q, and e3/e1, showed a strong correlation to the peel and shear results while the parameters, S, T, and v3/v1, demonstrated weaker dependencies. While detailed molecular level interpretation of the LAOS results is not possible, these results indicate LAOS testing may provide a better indication of applications performance in a more efficient way than existing applications test protocols.

Enhanced Heat Resistance of Acrylic Pressure-Sensitive Adhesive by Incorporating Silicone Blocks Using Silicone-Based Macro-Azo-Initiator

To improve the heat resistance of acrylic-based pressure-sensitive adhesive (PSA), silicone-block-containing acrylic PSAs (SPSAs) were synthesized using a polydimethylsiloxane (PDMS)-based macro-azo-initiator (MAI). To evaluate the heat resistance of the PSA films, the probe tack and 90° peel strength were measured at different temperatures. The acrylic PSA showed that its tack curves changed from balanced debonding at 25 °C to cohesive debonding at 50 °C and exhibited a sharp decrease. However, in the case of SPSA containing 20 wt% MAI (MAI20), the balanced debonding was maintained at 75 °C, and its tack value hardly changed with temperature. As the MAI content increased, the peel strength at 25 °C decreased due to the microphase separation between PDMS- and acryl-blocks in SPSA, but the shear adhesion failure temperature (SAFT) increased almost linearly from 41.3 to 122.8 °C. Unlike stainless steel substrate, SPSA showed improved peel strength on a polypropylene substrate due to its low surface energy caused by PDMS block. Owing to the addition of 20 wt% silicone-urethane dimethacrylate oligomer and 200 mJ/cm2 UV irradiation dose, MAI20 showed significantly increased 90° peel strength at 25 °C (548.3 vs. 322.4 gf/25 mm for pristine MAI20). Its heat resistance under shear stress assessed by shear adhesion failure test (SAFT) exhibited raising in failure temperature to 177.3 °C when compared to non-irradiated sample.

Cellulose Nanocrystal (CNC)-Latex Nanocomposites: Effect of CNC Hydrophilicity and Charge on Rheological, Mechanical, and Adhesive Properties.

Cellulose nanocrystals (CNCs), a sustainable nanomaterial, are in situ incorporated into emulsion-based pressure-sensitive adhesives (PSAs). Commercially available CNCs with different surface hydrophilicity and surface charge (CNC101 and CNC103 from CelluForce) are used to explore their role in PSA property modification. Viscosity measurements and atomic force microscopy reveal differences in degree of association between the CNCs and the latex particles depending on the surface properties of the CNCs. The more hydrophilic and higher surface charge CNCs (CNC101) show less association with the latex particles. Dynamic strain sweep tests are used to analyze the strain-softening of the nanocomposites based on CNC type and loading. The CNC101 nanocomposites soften at lower strains than their CNC103 counterparts. This behavior is confirmed via dynamic frequency tests and modeling of the nanocomposites' storage moduli, which suggest the formation of CNC aggregates of, on average, 3.8 CNC101 and 1.3 CNC103 nanoparticles. Finally, PSA properties, i.e., tack, peel strength, and shear strength, simultaneously increase upon addition of both CNC types, although to different extents. The relationship between the PSA properties and CNC surface properties confirms that the less hydrophilic CNCs lead to improved CNC dispersion in the PSA films and therefore, enhance PSA properties.

Change of Characterization and Film Morphology Based on Acrylic Pressure Sensitive Adhesives by Hydrophilic Derivative Ratio.

Hydrophilic acrylic pressure-sensitive adhesives (PSAs) were synthesized by controlling the contents of 2-ethylhexyl acrylate (EHA), isobornyl acrylate (IBOA), and 2-hydroxyethyl acrylate (HEA); especially, the characteristic change of the HEA content was analyzed. Surface contact angle of acrylic PSA film decreased from 77.87° to 70.23° in the case of Acryl-2 to Acryl-8 (below HEA 10 wt %). However, the surface contact angle of Acryl-10 to Acryl-40 (HEA 10 wt % to 40 wt %) increased up to 92.29°, indicating hydrophobicity. All acrylic PSA films showed high adhesive force above 1800 gf/25 mm. According to X-ray diffraction (XRD) measurement, hydrophilic acrylic PSAs exhibited amorphous property and it was confirmed that the morphology of acrylic PSA film was significantly affected by the flexibility of the polymer chain and the strength of hydrogen bonding. The affinity with hydrophilic materials for acrylic PSA films was evaluated by T-type peel test, confirming that the affinity with hydrophilic materials is determined by the hydrophilicity of the acrylic PSA film. The synthesized acrylic PSA film is non-toxic regardless of the hydrophilicity.

Effect of dodecafluoroheptyl methacrylate (DFMA) on the comprehensive properties of acrylate emulsion pressure sensitive adhesives

Fluorinated acrylate emulsion pressure sensitive adhesives (PSA) based on butyl acrylate (BA), fluorine monomer dodecafluoroheptyl methacrylate (DFMA), acrylic acid (AA) and 2-hydroxyethyl acrylate (HEA) were synthesized via a monomer-starved seeded semi-continuous emulsion polymerization process. The influences of DFMA on the resultant latex and PSA properties were comprehensively investigated. FTIR analysis indicated that DFMA could be successfully introduced into the latex PSA copolymer through emulsion polymerization. DSC and TG analyses showed that Tg and thermal stability of the PSA were both improved as DFMA content increased. XPS analysis indicated that fluoroalkyl groups had a tendency to enrich on the surface of the film, and the more DFMA added the more F content on the film surface. Moreover, the surface roughness and contact angle of the acrylate latex PSA film were both increased with the introduction of DFMA. Dynamic mechanical analysis (DMA) and adhesive property tests showed that the storage modulus (Gʹ) and shear holding power were improved with DFMA content while at the sacrifice of loop tack. Finally, 180° peel strength of fluorinated acrylate latex PSAs on different substrates (PP, SS) as a function of DFMA content was evaluated.

The use of lignin in emulsion-based pressure-sensitive adhesives

Pressure sensitive adhesive (PSA) films were produced by in situ seeded semi-batch emulsion polymerization of butyl acrylate (BA) and methyl methacrylate (MMA) in the presence of varying amounts of lignin. Two types of Kraft lignin, water-soluble and non-water soluble, were used in this study. Lignin was modified using acrylation (methacryloyl chloride), maleation (maleic anhydride) and acetylation (acetyl bromide and acetic acid) to promote its miscibility with the BA and MMA monomers and encourage its incorporation into the polymer matrix. For the case of the maleated lignin, maximum incorporation of 10 wt% was achieved whereas, for the acrylated lignin case, a maximum of 5 wt% was attained. Lignin was shown to decrease latex viscosity in all cases. At a lignin loading of 1 wt% (relative to the amount of monomer) a tack and shear strength of the PSA films increased significantly while the peel strength remained constant. Thus, maleated lignin was shown to be an effective, renewable modifier for emulsion-based PSA properties.

Shock absorption of semi-interpenetrating network acrylic pressure-sensitive adhesive for mobile display impact resistance

With the development of mobile display shapes from flat to flexible, the conventional glass cover window must be replaced by a film-type window. However, film-type cover windows have low impact resistance owing to their poor shock absorption. Therefore, to realize their application to flexible displays, it is essential to characterize and improve the shock-absorbing characteristics of the display film. In this study, a semi-interpenetrating network (semi-IPN) acrylic pressure-sensitive adhesive (PSA) consisting of a crosslinked network structure with a linear acrylic polymer chain was developed. The influence of the multi-functional monomer content and UV dose on the properties of the semi-IPN PSA was studied. The peel strength of the semi-IPN PSA was higher than 10 N/25 mm, which is generally considered as the PSA standard for mobile displays. With an increase in crosslink density, the storage modulus increased, but the damping factor decreased. To evaluate shock absorption, a falling ball impact tester was used to estimate the shock absorption ratio (ΔF) of the film. The semi-IPN PSA incorporating 30 phr of the multi-functional monomer exhibited higher ΔF (31.2%) than that of a conventional UV-curable PSA film (24.6%). This shows that even with the relatively low damping factor of the semi-IPN PSA, its structure could improve shock absorption. Moreover, we suggested two mechanisms for shock absorption of the semi-IPN PSA, energy dissipation into the PSA layer and extended contact time.