High Peel Strength Research Articles

High thermal stability and low impedance polypropylene separator coated with aluminum phosphate

Separators with low ionic impedances and high thermal/electrochemical stability are desirable for high-performance Li-ion batteries. Herein, a composite layer consisting of AlPO4, poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) and polymethyl methacrylate (PMMA) is coated on the polypropylene (PP) separator matrix. The coated PP exhibits an electrolyte uptake of 2.28%, leading to improved ionic conductivity and Li-ion diffusion coefficient. In addition, this separator has a wide electrochemical stability window, high peeling strength of 111.2 N m−1 and superior thermal stability at 170 °C. By applying this coated separator in the cell with LiNi0.5Co0.2Mn0.3O2 cathode, excellent cycling stability and rate performance can be also obtained. The improved electrochemical performances can be attributed to that AlPO4 in the coating layer exhibits high electrolyte uptake and firmly combines with the PP matrix.

Investigation of the effect of green laser pre-treatment of aluminum alloys through a design-of-experiments approach

The present study aims to investigate a surface treatment process performed by a pulsed Ytterbium green fiber laser on aluminum 2024 coupons. An evaluation of the process parameters effect as well as a statistical optimization of the process is attempted with the aim to improve the mechanical performance of adhesively bonded joints. The process parameters under investigation are the scanning speed, the pulse frequency and the hatching distance whereas the targeted objectives to be optimized are the surface wettability as well as the quality of adhesion as characterized by the Sessile Drop Technique and the Floating Roller Peel Test respectively. A design of experiments approach is implemented to search as effectively as possible the process parameters space. A Box-Behnken three-level factorial design was used to define the minimum number of experimental trials and build an appropriate test matrix. Finally, Analysis of Variance was implemented to assess the influential parameters. The set of parameters that optimize the objective of high peel strength and surface (super)hydrophilicity were identified following a response surface methodology. In order to understand and evaluate the experimental results and the underlying mechanisms, scanning electron microscopy (SEM) and chemical analysis with X-ray photoelectron microscopy (XPS) of the laser-treated surfaces were performed. In conclusion, it has been demonstrated that the laser surface treatment of aluminum alloy is an extremely promising dry treatment method, capable of improving the performance of adhesive bonding.

Effect of hexagonal boron nitride on the thermal and dielectric properties of polyphenylene ether resin for high-frequency copper clad laminates

As the base material of the printed circuit boards (PCBs), copper clad laminates (CCLs) with high thermal conductivity, low dielectric loss and high peel strength have been greatly desired especially for the upcoming 5G age. In this study, hexagonal boron nitride (hBN) was firstly introduced into the polymer insulating filler (Polyphenylene ether resin, PPER) of copper clad laminates for high frequency applications. The as-obtained CCLs exhibited a high thermal conductivity up to 1W/m·K and a low dielectric loss of ~4×10−3. Meanwhile, the interface tailoring of hBN was also tried by SiO2 coating, which enhanced the peel strength to a maximum value of 1.1N/mm, but changed the thermal conductivity behavior of the CCLs from the Agari's linear model to the modified quadratic model due to the interfacial thermal resistance effect of SiO2 coating on hBN. Moreover, the flexural strength and water absorption were also tested. The results revealed that, comparing with the related composite materials reported in literature and commercial products, the CCLs obtained in this paper have outstanding advantages in thermal and dielectric properties, validating the high potential of the present CCLs for use in high frequency PCBs.

Investigation of a pulsed laser ablation process for bonded repair purposes of CFRP composites via peel testing and a design-of-experiments approach

The present study aims to investigate an automatic material ablation process performed by a pulsed Ytterbium green fiber laser for bonded repair purposes of carbon fibre reinforced composites. The investigated process parameters are the scanning speed, the pulse frequency, the hatching distance and the hatching pattern whereas the targeted objectives are the material removal rate as well as the quality of adhesion as characterized by a novel composite peel test. The use of a green laser, if properly implemented and optimized, turns out to offer a series of advantages. Not only it allows the precise, controllable and automatic -without human intervention-material ablation but it can change the morphology of the CFRP surface through micro-machining effects such as the creation of novel highly regular micro-structural formations that significantly enhance bonding. We provide with experimental evidence that this is not always the case but happens only for specific levels of the process parameters. A design of experiments approach is implemented to search as effectively as possible the process parameters space. We utilize a Box-Behnken four-level factorial design to define the minimum number of experimental trials and build an appropriate test matrix. Analysis of variance is finally implemented to assess the influential parameters. Finally, the set of parameters that optimize the objective of simultaneously high peel strength and material removal rate are identified following a response surface methodology.

Fabrication and Fatigue Behavior of Aluminum Foam Sandwich Panel via Liquid Diffusion Welding Method

Aluminum Foam Sandwich panels were fabricated via liquid diffusion welding and glue adhesive methods. The Microstructure of the Aluminum Foam Sandwich joints were analyzed by Optical Microscopy, Scanning Electron Microscopy, and Energy Dispersive Spectroscopy. The metallurgical joints of Aluminum Foam Sandwich panels are compact, uniform and the chemical compositions in the diffusion transitional zone are continuous, so well metallurgy bonding between Aluminum face sheet and foam core was obtained. The joining strength of an Aluminum Foam Sandwich was evaluated by standard peel strength test and the metallurgical joint Aluminum Foam Sandwich panels had a higher peel strength. Moreover, a three-point bending fatigue test was conducted to study the flexural fatigue behavior of Aluminum Foam Sandwich panels. The metallurgical joint panels have a higher fatigue limit than the adhesive joining sandwich. Their fatigue fracture mode are completely different, the failure mode of the metallurgical joint is faced fatigue; the failure mode for the adhesive joint is debonding. Therefore, the higher joining strength leads to a longer fatigue life.

Preparation of high peel strength and high anti-aging epoxy adhesive that used for bonding aluminum alloy without surface treatment

In the case of bonding of aluminum alloy, surface pretreatment have been widely adopted for adherends so as to achieve superior adhesive performance. However, the strict surface treatment of the aluminum alloy cannot be implemented without special equipment and the mechanical properties, corrosion resistance and aging resistance of the common adhesives cannot meet the demand without surface treatment. Here, acrylic oligomer modified by carboxyl terminated organosilicon and nano alumina were used to modify an epoxy formulation based on a classical DGEBA monomer to produce a high peel strength epoxy adhesive that can be used without surface pretreatment. The peel strength and the shear strength of the adhesive could reach 7.18 N/cm and 18.75 MPa, respectively, and could be well maintained under −70 °C and 100 °C. The novel adhesive also has good heat aging resistance, water resistance and artificial seawater resistance. SEM and XPS were used to investigate mechanism of aging resistance of modified adhesives without surface treatment.

Single and dual adhesive bond strength analysis of single lap joint between dissimilar adherends

The emerging trends for joining of aircraft structural parts made up of different materials are essential for structural optimization. Adhesively bonded joints are widely used in the aircraft structural constructions for joining of the similar and dissimilar materials. The bond strength mainly depends on the type of adhesive and its properties. Dual adhesive bonded single lap joint concept is preferred where there is large difference in properties of the two dissimilar adherends and demanding environmental conditions. In this work, Araldite-2015 ductile and AV138 brittle adhesives have been used separately between the dissimilar adherends such as, CFRP and aluminium adherends. In the dual adhesive case, the ductile adhesive Araldite-2015 has been used at the ends of the overlap because of high shear and peel strength, whereas in the middle of the bonded region the brittle adhesive AV138 has been used at different dimensions. The bond strength and corresponding failure patterns have been evaluated. The Digital Image Correlation (DIC) method has been used to monitor the relative displacements between the dissimilar adherends. Finite element analysis (FEA) has been carried-out using ABAQUS software. The variation of peel and shear stresses along the single and dual adhesive bond length have been captured. Comparison of experimental and numerical studies have been carried-out and the results of numerical values are closely matching with the experimental values. From the studies it is found that, the use of dual adhesive helps in increasing the bond strength.

Structural engineering of SnS2/Graphene nanocomposite for high-performance K-ion battery anode

K-ion batteries (KIBs) are drawing increasing research interest as a promising supplement of Li-ion batteries due to the natural abundance of K resource. However, due to the large size of K+, high-capacity anodes are challenged by the structural stability of the active materials which are susceptible to large volumetric deformation after incorporating with a sufficient number of K+. Herein, using SnS2/graphene as an example, we demonstrated that high-performance KIBs anode could be achieved through collaborative efforts targeting on both the active material and the prepared electrode film. The electrochemically-active species of SnS2 were controlled into small nanoparticles with their size below 5 nm to provide sufficient reactive sites for K+ storage. Meanwhile, highly-resilient electrode film based on the prepared SnS2/graphene nanocomposite was built on aluminum (Al) current collector rather than the widely-used copper foil, forming a strong anode film with high peel strength to endure the potassiation/depotassiation process. In this way, the active species was able to deliver an extraordinary reversible capacity of 610 mAh g−1 with unprecedented high-rate capability (around 290 mAh g−1 at 2A g−1) and promising cycling stability. This contribution sheds light on the rational design of high-performance electrode for KIBs and beyond.

Property modification of a silicone acrylic pressure-sensitive adhesive with oligomeric silicone urethane methacrylate

A silicone acrylic pressure-sensitive adhesive (SPSA) was synthesized using a silicone macro-azo-initiator as an adhesive for low surface energy substrates. The SPSA had a high peel strength value on an SUS (steel use stainless) substrate due to its low surface energy; however, it had very low peel strength values on low surface energy substrates such as PP and PE. In this study, a silicone urethane dimethacrylate (SiUDMA) oligomer was synthesized as a modifier for the SPSA. The SiUDMA had a much lower viscosity and a slightly higher surface energy than the SPSA. The addition of SiUDMA increased the peel strength of the SPSA regardless of the substrate. In the case of the PP and PE substrates, the increase of peel strength with SiUDMA addition was remarkably large when compared to the SUS substrate because SiUDMA significantly reduced SPSA viscosity and improved its fluidity, consequently facilitating the wetting of the rough surfaces of PP and PE. The rough surfaces of PP and PE could also aid the spreading of SiUDMA-modified SPSA and enlarge the interfacial area. On the other hand, UV curing of SiUDMA and the SiUDMA-modified SPSA resulted in a serious decrease in the peel strength on the PP and PE substrates due to the decrease in the fluidity of the SPSA material, but the SAFT of SPSA increased with UV irradiation.

Isophorone Diisocyanate (IPDI) Microencapsulation for Mono-Component Adhesives: Effect of the Active H and NCO Sources.

Polyurea/polyurethane (PUa/PU) shell microcapsules (MCs), containing high loadings of isophorone diisocyanate (IPDI) in the core, were developed to enable the production of mono-component, eco-friendly and safer adhesive formulations for the footwear industry. IPDI microencapsulation was obtained via oil–in–water (O/W) microemulsion combined with interfacial polymerization. A methylene diphenyl diisocyanate (MDI) compound (a commercial blend of monomeric and polymeric species), with higher reactivity than IPDI and low viscosity, was added to the O phase to competitively contribute to the shell formation, improving its quality. Four different active H sources were tested, aimed at achieving a high encapsulation yield. The successful encapsulation of IPDI was confirmed by Fourier transformed infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), while the MCs’ morphology and size distribution were assessed by scanning electron microscopy (SEM). The incorporation of a multifunctional isocyanate silane in the O phase, as “latent” active H source, led to the formation of impermeable PUa/PU-silica hybrid shell MCs with more than 60 wt.% of pure encapsulated IPDI. A proof-of-concept study shows high peeling strength and a structural type of failure of the adhesive joint, revealing an effective IPDI release. These new engineered MCs are found to be promising crosslinkers for mono-component adhesives for high demanding applications.

Finely balanced high heat conductivity, peel strength and breakdown voltage in polymer composites with binary hybrid inorganic fillers

Nowadays, the demand of polymer based composites with high thermal conductance is rapidly increasing. Thermal conductive acrylate pressure sensitive adhesives are widely studied due to their excellent ageing resistance, light resistance, water resistance, oil resistance and broad application field. In this work, thermal conductive pressure sensitive adhesives with excellent comprehensive performances have been prepared from acrylate pressure-sensitive adhesive (matrix) and aluminum oxide/aluminum nitride particles (fillers). The influences of the class, loading content and grain size of fillers on heat conductivity, electric insulation and mechanical features of composites were deeply researched. High dispersion of fillers in matrix could be obtained by surface modification of fillers using silane coupling agent and polymethyl methacrylate. Heat conductivity of composites was improved with increasing of filler content and sharply elevated at a critical filler content. As filler content was increased, electric insulation trait was reduced but still kept at a relatively high level. High filler content was harmful to mechanical property. Fortunately, the composites with hybrid fillers of varied grain sizes were found to have significantly promoted thermal conducting, electric insulating and mechanical performances in comparison with single filler of one size. That might be ascribed to synergistic effect of both fillers with varied grain sizes. Finely balanced comprehensive features were achieved at a weight ratio of 3:7 (small size filler/large one). High heat conductivity (∼0.83 W m−1K−1), breakdown voltage (∼1.9 kV) and 180° peel strength (∼8.3 kN m−1) were obtained. This work might open the door to the large-scale fabrication of high-performance thermal conductive acrylic pressure sensitive adhesives based on size effect of hybrid fillers.

Acetyl-protected cytosine and guanine containing acrylics as supramolecular adhesives

ABSTRACTHydrogen bonding among nucleobase pairs serves as an efficient noncovalent interaction for designing supramolecular polymers with desired properties for pressure sensitive adhesives. Michael addition yielded acetyl-protected cytosine/guanine containing acrylic monomers with flexible spacers between the hydrogen bonding units and the acrylic backbone. Free radical polymerization of nucleobase-containing monomers afforded acetyl-protected cytosine/guanine homopolymers and random copolymers with n-butyl acrylate. Nucleobase incorporation significantly affected thermal, thermomechanical, rheological, morphological properties, and adhesive performance of polyacrylates. Guanine/cytosine-containing copolymers each exhibited a single glass transition (Tg) that increased with increasing nucleobase content. Self-association of acetyl cytosine and acetyl guanine units converted low Tg polyacrylates to physically crosslinked networks with mechanical integrity. Solution casting acetyl guanine-containing copolymers with 8 mol% or higher guanine content yielded free-standing films with microphase-separated morphologies. Acetyl cytosine-containing copolymers with 15 mol% or more cytosine formed free-standing films with less microphase-separation compared to the guanine copolymers. 1H NMR titration experiments established a 1:1 binding stoichiometry between acetyl cytosine and acetyl guanine monomers in CDCl3, similar to guanine-cytosine association. However, the acetyl protecting group hindered the formation of triple hydrogen bonding, resulting in double hydrogen bonding between acetyl cytosine and acetyl guanine with an intermediate binding strength comparable to their self-associations. Acetyl guanine-containing copolymers with 3 mol% acetyl guanine exhibited higher peel strength on stainless steel and higher extended service frequency range compared to cytosine-containing copolymers and various pressure sensitive adhesive controls.

Synthesized amino-functionalized porous clay heterostructure as an effective thickener in waterborne polyurethane hybrid adhesives for lamination processes

The use of waterborne polyurethane (WPU) adhesives with non-volatile organic compounds (non-VOCs) has essentially expanded in laminating adhesive applications due to stringent environmental regulations, including on the release of VOCs. To function well, the inferior properties of WPUs should be overcome with good adhesion and cohesion mechanisms. High-performance WPU adhesive was synthesized by incorporating an amino-functionalized porous clay heterostructure (APCH) into the WPU to increase its internal strength via formation of urea linkages between fillers and the polymer matrix, to yield an organic/inorganic hybrid adhesive with greater cohesion. Urea linkages, as characterized by Fourier-self deconvolution of the C=O stretching vibration region (1600−1800cm−1), increased with increasing APCH content. In addition, APCH significantly enhanced the adhesion properties of bonded joints together with an improved thermal stability of the adhesive, affirmed by the DSC analysis and higher viscosity observed by a Brookfield viscometer. The highest peel strength (126N/m) was achieved with a WPU hybrid adhesive containing 2.0wt% APCH, which can be used for application in untreated oriented polypropylene (OPP) lamination.

Direct bonding of copper and liquid crystal polymer

Copper (Cu) film bonded with polymer substrates offers better dimensional stability than that of deposited Cu especially in humid environment. However, poor adhesion is an issue in both cases. In this paper, we demonstrate a two-step, low temperature direct bonding technique for liquid crystal polymer (LCP) and copper (Cu) using oxygen plasma. The bonded interface showed high peel strength. This strong adhesion is due to the interdiffusion of Cu and carbon atoms into LCP and Cu film respectively. These phenomena resulted in three-dimensional metal clusters of Cu atoms and islands at the LCP/Cu interface, which gradually diffuse into the LCP. Interfacial elemental analysis reveals an intermediate oxide layer formation due to Cu2O and CO.

Characterization and mechanical testing of polydopamine-adhered electroless copper films

Self-assembling polydopamine has shown great versatility as a multifunctional surface coating. This study investigates the adhesive properties of polydopamine used to bind electroless copper films to several polymer substrates widely used for commercial applications, including polyethylene (PE), polycarbonate (PC), poly(methyl methacrylate) (PMMA), and nylon 6,6. Each substrate was coated in a similar manner resulting in continuous copper films of 52±12nm in thickness. Transmission electron microscopy revealed a non-preferential polycrystalline microstructure of copper grains averaging 53±17nm in diameter with a range of 21nm to 123nm, indicating there is some overlap of grains in the film. Peel testing, tensile tests, and tribological oscillating wear tests were used to characterize the mechanical performance of the adhered copper films. The nylon substrate had the highest peel strength, 49±5mN/mm, while the remaining substrates ranged from 5 to 13mN/mm on average. Coated substrates were strained up to 20% tensile strain to investigate film delamination, buckling, and rupture. Transverse buckling of the films relative to the direction of strain was observed due to Poisson's effect during tension. Films on nylon substrates resisted buckling and rupture up to 20% strain, whereas buckling, delamination, and rupture was observed in the other substrates below 20% strain. Tribological testing revealed that the coefficient of friction was governed by the polymer substrate and was not dependent upon the polydopamine or copper films. As a demonstration of the robust nature of this method, a nylon suture was coated with polydopamine-adhered copper film and tied in a knot to show a large complex deformation state without showing signs of delamination.

Joining sheet aluminum AA6061-T4 to cast magnesium AM60B by vaporizing foil actuator welding: Input energy, interface, and strength

Dissimilar joining of sheet aluminum AA6061-T4 to cast magnesium AM60B was achieved by vaporizing foil actuator welding (VFAW). Three input energy levels were used (6, 8, and 10kJ), and as a trend, higher input energies resulted in progressively higher flyer velocities, more pronounced interfacial wavy features, larger weld zones, higher peel strengths, and higher peel energies. In all cases, weld cross section revealed a soundly bonded interface characterized by well-developed wavy features and lack of voids and continuous layers of intermetallic compounds (IMCs). At 10kJ input energy, flyer speed of 820m/s, peel strength of 22.4N/mm, and peel energy of 5.2J were obtained. In lap-shear, failure occurred in AA6061-T4 flyer at 97% of the base material’s peak tensile load. Peel samples failed along the weld interface, and the AM60B-side of the fracture surface showed thin, evenly-spaced lines of Al residuals which had been torn out of the base AA6061-T4 in a ductile fashion and transferred over to the AM60B side, indicating very strong AA6061-T4/AM60B bond in these areas. This work demonstrates VFAW’s capability in joining dissimilar lightweight metals such as Al/Mg, which is expected to be a great enabler in the ongoing push for vehicle weight reduction.

Mixed Rigid and Flexible Component Design for High-Performance Polyimide Films.

To develop the polyimide (PI) which is closely matched to the coefficient of the thermal expansion (CTE) of copper, a series of PIs are prepared from 5,4′-diamino-2-phenyl benzimidazole (DAPBI), 4,4′-diaminodiphenyl ether (ODA), and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) using a sequential copolymerization, blade coating, and thermal imidization process. The physical properties of the PIs are effectively regulated and optimized by adjusting the ratio of the rigid DAPBI and flexible ODA components. By increasing the DAPBI content, thermal stability, dimensional stability, and mechanical properties, the resultant polymer is enhanced. PI-80 exhibits an excellent comprehensive performance, a glass transition temperature of 370 °C, and a tensile strength of 210 MPa. Furthermore, the CTE as calculated in the range 50–250 °C is ca. 19 ppm/K, which is equal to that of copper. A highly dimensionally stable, curl-free, and high T-style peel strength (6.4 N/cm) of copper/PI laminate was obtained by casting the polyamic acid onto copper foil (13 μm) and thermally curing at 360 °C, which indicates that it has the potential to be applied as an electronic film for flexible displays and flexible printed circuit boards. A structural rationalization for these remarkable properties is also presented.

Preparation of pressure-sensitive adhesives from tung oil via Diels-Alder reaction

In this study, tung oil was polymerized with a dimaleimide (4,4’-methylene-bis(N-phenylmaleimide) (MPMI) and two diacrylates (poly(propylene glycol) diacrylate (PPGDA) and bisphenol A glycerolate diacrylate (BPAGDA) via Diels-Alder reaction (DA reaction) to prepare pressure-sensitive adhesives (PSAs). On the one hand, the polymer of tung oil and MPMI was readily prepared however it was too rigid to serve as a PSA. On the other hand, the polymerization of tung oil with PPGDA or BPAGDA resulted in PSAs with peel strengths ranging from 0.1 to 0.2Ncm−1 and loop tacks ranging from 0.4 to 0.5N. Nevertheless, tung oil reacted readily with acrylic acid to form adducts (TOAA) with lower content of conjugated diene groups than those of tung oil. The use of TOAAs instead of tung oil to polymerize PPGDA failed to increase the peel strength of the resulting PSAs. However, polymerizations of TOAAs with BPAGDA resulted in PSAs with much higher peel strengths and much higher loop tacks than the polymerization of tung oil with BPAGDA. In addition, the introduction of a small amount of MPMI in the polymerization of TOAA and PPGDA significantly shortened the curing time.

Laser assisted additive manufacturing of continuous fiber reinforced thermoplastic composites

Herein, we proposed a novel laser assisted additive manufacturing (AM) methodology that utilizes prepreg composites (glass fiber-polypropylene) with continuous fiber reinforcement to fabricate 3D objects by implementing laser assisted bonding and laser cutting. The microstructure analysis demonstrated no visible void content and excellent interfacial bonding. The bonding strength of the proposed method was evaluated through lap shear strength and peel strength testing; resulting in 50% higher peel strength than hot compaction method, with lap shear strength up to 96% of compression molding benchmark data. Tensile properties of components printed by our method were superior to those of fused deposition modeling (FDM) printed short fiber composites with 300% and 150% of increase in tensile strength and modulus, respectively. Tensile strength of our printed components was comparable to compression molding and stamping, however, tensile modulus was 50% lower in average. Flexural strength of the laser assisted AM parts was also in the range of stamping and compression molding methods, with flexural modulus up to 100% higher than these methods. Overall, our proposed new technique offers an alternative direction in AM of continuous fiber reinforced thermoplastic polymer composites to solve the issues associated with current techniques.

Effect of the type of plasma on the polydimethylsiloxane/collagen composites adhesive properties

Polydimethylsiloxane (PDMS) films were treated with either oxygen (O2), nitrogen (N2) or argon (Ar) plasma between 40W and 120W for 5–15min and their surface properties studied by contact angle measurements, infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Lower contact angles and increases in surface roughness, assessed by SEM and AFM, were observed for all used gases when plasma power and time increased, with argon treatment being the one that showed the most significant change in roughness.PDMS/collagen type I composites obtained after treating PDMS with oxygen at 80W for 13min or nitrogen and argon at 80W for 14min showed a peel strength of 0.1N/mm (oxygen plasma), 0.08 N/mm (nitrogen plasma) and 0.09 N/mm (argon plasma). In all cases, peel strength was higher than that measured for the untreated bilayer composite. An increase in adhesion strength, after oxygen and nitrogen plasma, was mostly attributed to chemical interaction between functional groups introduced on the PDMS surface and the functional groups on collagen as detected by FTIR. In contrast, the high peel strength observed on PDMS treated with argon plasma was attributed to its increased roughness which in turn increased mechanical interlocking. The properties of these composites render them suitable for adhesive free skin substitutes.