Hydrophobic or Hydrophilic Fumed Silica as Filler of Polyurethane Adhesives

Two hydrophilic and two hydrophobic fumed silicas of different characteristics were added to solvent-based polyurethane adhesives (PU). IR spectroscopy, contact angle measurements and rheology (viscosity measurements, determination of viscoelastic properties) were used to monitor the variation of properties of PU adhesives produced by addition of silica. Immediate (green) adhesion was determined by T-peel testing of halogenated synthetic rubber/PU adhesive/halogenated synthetic rubber joints. Silica addition produced a noticeable increase in the PU adhesive viscosity which can be related to the variation of viscoelastic properties. Viscosity of PU adhesives containing hydrophilic silica slightly increased with time after preparation; the increase was less significant in PU adhesives with hydrophilic silica. In the rheological studies, silica imparted shear thinning and negative thixotropy to PU adhesives due to a better dispersion of the silica in the polyurethane during shearing. The addition of silica produces an increase in the storage modulus (G') of PU adhesives, the values obtained being independent of the hydrophilic or hydrophobic nature of the fumed silica. The increase of G' and the changes in tan δ of PU adhesives containing silica corresponded to an improvement in the green adhesion properties of chlorinated rubber/PU adhesive/chlorinated rubber joints. In general, in disagreement with previous results,¹ the presence of silica did affect the properties of solvent-based PU adhesives, but these properties were not dependent on the type of silica (hydrophobic or hydrophilic) used in this study.     

Recent Advances in Boron Nitride Based Hybrid Polymer Nanocomposites

Boron nitride (BN) is an eminent inorganic compound having many interesting characteristics such as improved oxidation resistance, mechanical strength, good thermal conductivity (TC), higher bandgap, high chemical stability, thermal stability, high hydrophobicity, and electrical insulation. The use of BN as a filler in polymers is a well-established strategy to tailor the properties of polymer composites. Recent studies depict an interesting urge to reap the synergistic effect of various nanofillers with BN in the form of hybrids. Hence the consolidation of the works on BN based hybrid fillers would definitely attract researchers so that these new filler systems could be transformed into useful polymer nanocomposites in future. This review article focuses on the synthesis and characterization of various boron nitride based hybrids in detail. Moreover, the review also throws light on different BN hybrid reinforced polymer nanocomposites (PNCs) and their thermal, electrical, electronic as well as biomedical applications in a detailed manner. Thus the review anticipates serving as a tool toward understanding the recent trends in the field of boron nitride hybrid based ternary polymer composites.     

Preparation and characterization of thermally conductive thermoplastic polyurethane/h‐BN nanocomposites

Polyurethane nanocomposites are versatile engineering polymers with unique properties. In this study, nano hexagonal boron nitride containing thermoplastic polyurethane elastomers were prepared via melt blending and hot‐pressing techniques. The nanocomposites were characterized using Fourier transform infrared, differential scanning calorimetry, thermal gravimetric analysis, tensile tests, and thermal conductivity measurements. The surface morphology of the TPU/h‐BN composites was characterized by scanning electron microscopy. The optical properties of the composites were determined by UV transmittance measurements and as the amount of h‐BN increased, optical transparencies decreased dramatically. Nanocomposites displayed higher E‐modulus values and lower elongation at break values than the pure TPU elastomer. Char yields of TPUs increased with increasing h‐BN percentage. Moreover, thermal conductivity of the composite materials improved with the incorporation of h‐BN. POLYM. COMPOS., 35:530–538, 2014. © 2013 Society of Plastics Engineers     

Nano boron nitride laminated poly(ethyl methacrylate)/poly(vinyl alcohol) composite films imprinted with silver nanoparticles as gas barrier and bacteria resistant packaging materials

Herein, nano boron nitride (BN) laminated poly(ethyl methacrylate) (PEMA)/poly(vinyl alcohol) (PVA) nanocomposite films are fabricated by using a simple in situ polymerization technique with incorporation of silver nanoparticles (Ag NPs). Structural investigations of PEMA/PVA/Ag@BN nanocomposite thin films are carried out by Fourier-transform infrared spectroscopy, dynamic light scattering, X-ray diffraction analysis, ¹H nuclear magnetic resonance, ¹³C nuclear magnetic resonance, and mass spectrometry. The change in morphology of PEMA/PVA matrix due to the reinforcement of BN platelets are identified by electron microscopic studies. The unique tortuous paths are achieved by the dispersion of BN platelets by which gas penetration is restricted with enhancing the barrier properties of the material by 6.5 folds at 5 wt% BN content as compared with neat PEMA/PVA. Acid and alkali resistant along with biodegradability behavior of as-synthesized nanocomposites are studied. From limiting oxygen index (LOI) results, it is found that the prepared materials are fire retardant in nature owing to effective reinforcement of BN layers. Antibacterial activities of PEMA/PVA/Ag@BN nanocomposite are studied by Xanthomonas citri or axonopodis pv. Citri, Escherichia coli, and Xanthomonas oryzae pv. Oryzae because of Ag NPs reinforcement. The substantial improvements in gas barrier, fire retardant, and antibacterial properties enable the materials for packaging application.     

聚氨酯胶粘剂的研究进展

综述了聚氨酯胶粘剂的合成、特性和种类。概述了近年来国内外聚氨酯胶粘剂的研究和应用进展,重点介绍了聚氨酯胶粘剂的发展动态和几类主要的聚氨酯胶粘剂,并对其进行了分析,结合实际情况对今后聚氨酯胶粘剂的发展方向作出了展望。     

Preparation and Characterization of Electroconductive Adhesives of NanoG/Polyurethane-Epoxy IPNs

Polyurethanes (PU) based on toluene diisocyanate (TDI) and polypropylene glycol 2000 (PPG) were reacted with an epoxy resin (EP) to prepare interpenetrating polymer networks (IPNs). Three kinds of electroconductive adhesives were prepared by dispersing nano-graphite (NanoG) into different matrices, i.e., pure PU, crosslinked PU/EP, and pure EP. The effects of epoxy content on morphological structure, conducting properties, thermal stability, and adhesive properties of the electroconductive adhesives were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, standard digital multimeter, dynamic mechanical thermal analysis, and lapshear tests. The results indicate that epoxy in the polyurethane-epoxy IPN adhesives plays an important role in clanging the morphological structure and improving conductivity properties, thermal stability, and adhesive properties of the electroconductive adhesives of PU.     

Underwater polyurethane adhesive with enhanced cohesion by postcrosslinking of glycerol monomethacrylate

Polyurethane (PU) has been widely used as a glue in various areas. However, adhesion in the presence of water is greatly impeded and results in most synthetic adhesive failure. In this study, we designed and synthesized a novel PU construction; underwater PU adhesives were created by the incorporation of synthetic glycerol monomethacrylate (GMA). Furthermore, the urethane structure helped the adhesive eliminate the interfacial water barrier through interactions that were stronger than hydrogen bonding, and GMA as a crosslinking agent was used to generate post‐covalent‐crosslinking networks through radical polymerization. This enhanced the cohesion so the diffusion of water molecules could be overcome. Fourier transform infrared spectroscopy, thermogravimetric analysis, underwater adhesion measurements, and tensile tests were used to characterize the chemical and mechanical properties of the as‐obtained adhesive. This led to an adhesive with a better mechanical strength and interfacial adhesion in water, and the results show that the mechanical properties (tensile strength, Young's modulus, and tensile elongation) of the GMA–PU adhesive were higher than those of the pure PU. As for the 4% GMA, the tensile strength was enhanced by 24.3% and the elongation was enhanced by 125.23% over those of the pure PU. This confirmed that the incorporation of GMA into the PU matrix indeed induced increasing cohesion, and the sample's adhesive strength was 21.19 ± 3.9 MPa; this indicated a superior adhesive strength over that of the pure PU. In addition, we can foresee that underwater adhesion will play an important role in prospective surgery and engineering areas. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46579.     

Study of the correlation between flexible food packaging peeling resistance and surface composition for aluminum-metallized BOPP films aged at 60°C

ABSTRACT

This study investigated the correlation between surface composition and peeling resistance in food packaging films by studying the heat aging of fabricated films over varying periods of time. The films consisted of a layer of aluminum (Al) metallized, biaxially oriented polypropylene (BOPP) bonded with a polyurethane (PU) adhesive onto another polymeric layer of low-density polyethylene (LDPE). The Al metallized films were prepared by physical vapor deposition (PVD) and aged at 60°C for either 5 or 15 days. The resulting aluminum surfaces were analyzed using X-ray photoelectron spectroscopy (XPS) and found to contain aluminum oxide (Al₂O₃) and trihydroxide (Al(OH)₃). The XPS characterization also revealed a 29% increase in the Al(OH)₃ layer thickness of the aged sample relative to a non-aged sample. Atomic force microscopy (AFM) was applied on investigations of possible morphology changes. The aluminum and PU adhesive surface energies were also determined using contact angles measurements and the aluminum surface energy was found to increase by as much as 11.7% compared to the non-aged sample, while the PU adhesive surface energy was at least 65% higher than that of the metallic substrate. The peeling resistance of the laminated aluminum was determined by average peel strength measurements and it was found that the variation in peel strength was related to changes in the Al₂O₃ layer thickness. The delaminated samples were analyzed using scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS) and showed the cohesive failure of the aluminum film.     

Adhesive based on micellar lupin protein isolate exhibiting oxygen barrier properties

In order to minimize the utilization of non‐renewable fossil resources, novel polymer sources for food packaging are being investigated. Micellar Lupin Protein (MLP), produced by dilution precipitation has great potential as functional laminating adhesive due to its high adhesion‐ and oxygen‐barrier properties. Formulations of MLP are used as laminating adhesive between high density‐polyethylene foil and paper as well as coating for poly(ethylene terephthalate) foil. The application of glycerol, sorbitol and combinations thereof as plasticizers are being investigated. Adhesive behavior as well as oxygen‐ and water vapor barrier properties were tested. The addition of both plasticizers enabled the preparation of processable coatings showing coherent and homogeneous morphology with improved adhesive behavior and oxygen barrier. When using sorbitol oxygen permeation coefficients of 0.93 cm³ (STP) 100 µm m^?2 d^?1 bar^?1 were achieved. The laminates containing only sorbitol provided adhesion properties comparable to standard polyurethane laminates with cohesion failure in 100% of the by T‐Peel‐Test examined cases. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46383.     

Comparison of the Properties of Polyurethane Adhesives Containing Fumed Silica or Sepiolite as Filler

Fumed silica is a well-known mineral filler of epoxy and polyurethane adhesives. Although effective, the small particle size and the relative high cost of fumed silicas suggest the need for an alternative filler. In this study, the usefulness of adding a natural hydrated magnesium silicate (sepiolite) as a new filler in solvent-based polyurethane (PU) adhesive formulations has been demonstrated. The rheological and adhesion performance of the sepiolite-filled PU adhesive was compared with that in PU adhesives containing fumed silicas. The addition of a filler to PU adhesives provided an increase in viscosity, imparted thixotropy and pseudoplasticity to the adhesive solution, produced an increase in storage and loss moduli, and improved the rheology of the PU. The mechanical properties of adhesive films were increased by adding filler, mainly with fumed silica. On the other hand, the immediate T-peel strength of roughened or (roughened + chlorinated) styrene-butadiene rubber/PU adhesive joints was greatly improved in filled PU adhesives. The effects produced by adding sepiolite or fumed silica to the adhesives were very similar, although in general more noticeable in fumed silica filled PU due to the formation of hydrogen bonds between the filler and the solvent and/or the polyurethane (in sepiolite-filled adhesives, van der Waals forces seemed to be responsible for the interactions between the filler and the solvent and/or polyurethane).     

Morphologies and properties of nanocomposite films based on a biodegradable poly(ester)urethane elastomer

Biodegradable poly(ester)urethane (PU) elastomer‐based nanocomposite films incorporated with organically modified nanoclay were prepared with melt‐extrusion compounding followed by a casting film process. These films were intended for application as biodegradable food packaging films, with their enhanced gas barrier, mechanical, and thermal properties and good flexibility. From both X‐ray diffraction measurements and transmission electron microscopy observations, the coexistence of intercalated tactoids and exfoliated silicate layers in the compounded PU/clay nanocomposite films was confirmed. In addition, the morphology exhibited a clay dispersion state in the matrix and was influenced by the incorporated nanoclay content. The effects of the nanoclay loading level on the thermal, mechanical, and barrier properties of the compounded nanocomposites were also investigated. As a result, it was revealed that the addition of nanoclay up to a certain level resulted in a remarkable improvement in the thermal properties in terms of thermal stability and the degree of thermal shrinkage; mechanical properties, including dynamic storage modulus and tensile modulus; and oxygen/water‐vapor barrier properties of the nanocomposite films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

聚氨酯胶黏剂

综述了聚氨酯胶黏剂的特性和种类,以及国内聚氨酯胶黏剂研究现状;概述了近年来国内外聚氨酯胶黏剂研究和应用进展,重点介绍了鞋用聚氨酯胶黏剂、汽车用聚氨酯胶黏剂、包装用聚氨酯胶黏剂、建筑用聚氨酯胶黏剂以及木材用聚氨酯胶黏剂等的研究进展,并对其进行了分析,结合实际情况对今后聚氨酯胶黏剂的发展方向做出了展望,指出聚氨酯胶黏剂在蒸煮袋复合薄膜及水性聚氨酯胶黏剂和反应热熔胶方面的实际需求。     

Evaluation of polypropylene/montmorillonite nanocomposites as food packaging material

The aim of this study was to use nanocomposites of polypropylene (PP) and montmorillonite (MMT), prepared by melt intercalation in a twin-screw extruder, as a food packaging material. The nanocomposites were evaluated by thermal, mechanical, and morphological analyses. Measurements of oxygen and water vapor permeability were also conducted to the nanocomposites. Besides, orange juice was used as modeling food and its physical–chemical and microbiological properties were determined. Despite of no significant changes in tensile properties were observed to the nanocomposites, the impact strength presented a substantial enhancement and the rigidity as well. Besides, MMT have shown a high capacity to improve oxygen barrier properties of PP. Electronic microscopy revealed certain homogeneity, showing some MMT-exfoliated lamellae in the PP matrix. Regarding the package efficacy, the orange juice quality was maintained after 10 days of storage. Concluding, this study seems to clarify a little more the claimed efficiency of nanocomposites as food packing materials.     

Preparation and properties of thermally conductive photosensitive polyimide/boron nitride nanocomposites

A new thermally conductive photoresist was developed. It was based on a dispersion of boron nitride (BN) nanoflakes in a negative‐tone photosensitive polyimide (PSPI) precursor. 3‐Mercaptopropionic acid was used as the surfactant to modify the BN nanoflake surface for the dispersion of BN nanoflakes in the polymer. The thermal conductivity of the composite films increased with increasing BN fraction. The thermal conductivity of the PSPI/BN nanocomposite was up to 0.47 W m⁻¹ K⁻¹ for a mixture containing 30 wt % nanosized BN filler in the polyimide matrix. Patterns with a resolution of 30 μm were obtained from the PSPI/BN nanocomposites. The PSPI/BN nanocomposites had excellent thermal properties. Their glass‐transition temperatures were above 360°C, and the thermal decomposition temperatures were over 460°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrical and mechanical properties of electrically conductive adhesives from epoxy,micro-silver flakes,and nano-hexagonal boron nitride particles after humid and thermal aging

In this study, we incorporated micro-silver flakes and nano-hexagonal boron nitride (BN) particles into a matrix resin to prepare electrically conductive adhesives (ECAs). The humid and thermal aging results under a constant relative humidity level of 85% at 85 °C revealed that the aged ECAs containing 3 wt% of nano-hexagonal BN particles had high reliability. The contact resistance was low and the shear strength high. Nano-hexagonal BN particles have a good effect on the reliability of ECAs that can be used to improve the properties of ECAs.     

Accelerated aging and contact with food simulants in adhesion of amorphous hydrogenated carbon films obtained by the PECVD process from recycled PET from packaging

This work focuses principally on the influence of time, temperature, and contact with food simulants in adhesion of amorphous hydrogenated carbon (a‐C:H) films obtained by the plasma enhanced chemical vapor deposition process in recycled PET from packaging. Shelf life of packaging used in soft drinks, fruit juice, etc. is known to be ～ 6 months, with possible variations. The a‐C:H film, used in this study as a functional barrier against possible contaminants in recycled PET, was analyzed to determine possible alterations in its physical and chemical properties. The film underwent an accelerated aging test and was exposed to contact with food simulants listed by the FDA. In this case, adhesion is one of the properties most in need of conservation. This property was analyzed by means of the tape test and scanning electronic microscopy. Superficial chemical alterations resulting from both the accelerated aging test and contact with liquids were examined by the contact angle. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

High-temperature oxidation of BN-coated sylramic SiC fibers in dry and wet atmosphere

The oxidation behavior of SiC Sylramic fibers coated with chemically vapor deposited Si-doped boron nitride (BN) was investigated at temperatures between 800 and 1200°C in dry and wet O₂ atmospheres. Thermogravimetric analysis was used to study the oxidation kinetics of the fiber and the influence of the BN layer and the environment. The morphology and composition of the thermally grown oxide scale was determined posttest by scanning electron microscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectrometry. This study gives new insights into the synergistic effects of BN and water vapor on the oxidation behavior SiC Sylramic fibers. The vulnerability of the BN fiber interphase and the behavior of the fiber under conditions relevant to high-temperature turbine applications are discussed.     

The Mechanisms of Peeling of Uncross-Linked Pressure Sensitive Adhesives

We analyze the peeling properties of an uncross-linked pressure sensitive adhesive. 90° peeling master curves on Pyrex^TM and PMMA (polymethylmetacrylate) are constructed The shift coefficients a_T are compared with the ones obtained from rheometrical shear tests.

With our machine, the peeling front is kept fixed, enabling us to observe the mechanisms of deformation of the adhesive. We count four different mechanisms of peeling in cohesive failure, and three in interfacial peeling (the last being unstable); they correspond to various slopes that we identify. The flow patterns at slow reduced velocities are two-dimensional. Then they undergo transitions to three-dimensional periodic complex flows, due to instabilities in the flow of thin adhesives. Interpretation of these peeling master curves are discussed in terms of rheology and physico-chemistry. It appears necessary to take into account the elongational properties of the adhesive, as well as the surface energy properties, to predict adhesion.     

Durability of green polyurethane adhesive bonded aluminum alloy in dry and hydrothermal ageing conditions

Polyurethane (PU) adhesives were prepared from the reaction of polycaprolactone (PCL) polyols based on palm kernel oil based polyesteramide (PPKO) with an aromatic and cycloaliphatic diisocyanate. Four different formulations of PU adhesives were prepared by varying the NCO : OH ratio, in order to investigate the effects of NCO : OH ratios on adhesion strength. The adhesive strength of metal–metal bonding both in dry and hydrothermal ageing—was determined by single lap shear joint testing. The resistance to hydrolysis of the PU adhesives was determined by performing water absorption tests. The water absorption test samples suggested that the durability of the adhesives correlated to lower water absorption due to higher NCO content. The correlation between the crosslinking of the PU network and adhesive strength was also studied by performing swelling tests. The higher NCO content showed that, the higher crosslink density of PUs led to higher cohesion and adhesion strengths. PU1.7 showed optimal properties in terms of durability and resistance to hydrolysis, whereas PU2.0 revealed deterioration in durability and resistance to hydrolysis due to the presence of greater micro‐voids content in the PU2.0 matrix. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41151.     

Effect of using sepiolite silicate + fumed silica mixtures as fillers on the characteristics of solvent-based polyurethane adhesives

Abstract —Both fumed silica and sepiolite have been used as a filler of polyurethane (PU) adhesives. Although effective, the small particle size and the relative high cost of fumed silica are limitations in some applications. Sepiolite is cheaper than fumed silica, but its relatively large particle size facilitates its settling from the adhesive solutions. In this study, the usefulness of using sepiolite + fumed silica mixtures as a filler in solvent-based PU adhesives is demonstrated. The rheological and adhesion properties of the PU adhesive solutions and the rheological and mechanical properties of the PU films (without solvent) were studied. SEM micrographs of PU films showed the morphology and compatibility of the fillers with the PU matrix. The use of sepiolite + fumed silica mixtures inhibited the settlement of the filler from the PU adhesive solutions, increased both the storage and the loss moduli, and improved the rheological and mechanical properties of the PU. On the other hand, the green (immediate) T-peel strengths of roughened styrene-butadiene rubber/PU adhesive joints and plasticized PVC/PU adhesive joints were greatly improved in filled PU adhesives. The effects produced by using fumed silica alone or sepiolite + fumed silica mixtures were very similar, although in general, somewhat more marked in fumed silica-filled PU.