Waterborne Polyurethane Adhesives Research Articles

A Review of Waterborne Polyurethane Coatings and Adhesives with Polyester Polyol from Poly(Ethylene Terephthalate) Waste

A Review of Waterborne Polyurethane Coatings and Adhesives with Polyester Polyol from Poly(Ethylene Terephthalate) Waste

Structural and adhesion properties of waterborne polyurethane adhesives containing nanosilica dispersion obtained with different physical mixing procedures

Nanosilica dispersion was added to waterborne polyurethane dispersion by using three different physical mixing procedures differing in the flow regime (tangential, laminar, radial) and the stirring rate (300–2400 rpm). The influence of the physical mixing procedure on the structural, thermal, rheological, mechanical, surface and adhesion properties of the polyurethanes (PUs) containing 1 wt% nanosilica was evaluated. The nanosilica in the dispersion was functionalized with acrylic moieties and showed high surface tension and negative Z potential values. The PU + nanosilica blend made with higher shear rate and laminar flow regime showed high homogeneous dispersion of the nanosilica particles and greater extent of intercalation between the soft segments of the polyurethane, this led to higher thermal stability. Unexpectedly, the better dispersion of the nanosilica in the PU matrix decreased the wettability of the PU + nanosilica materials due to the migration of acrylic moieties from the nanosilica particles to the surface. As a consequence, a decrease of the final T-peel strength was found. However, the single lap-shear strength did not change by adding nanosilica because of the scarce improvement of the mechanical properties in the PU + nanosilica materials.

Research of Properties and Preparation of Waterborne Polyurethane Adhesives for Shoes

In this paper, a waterborne polyurethane adhesive for shoes has been prepared by a composite method, and a series of tests such as peel strength, heat resistance, yellowing resistance, and hydrolysis resistance were performed on the sample. The results show that the performance of the water-based polyurethane adhesive prepared by this method has reached the level of similar products in the market. It has great promotion significance in shoe factories.

Effect of nonionomer emulsifier on particle stability of waterborne polyurethane adhesives

Polyurethane is one of the most versatile polymeric materials and is found just about everywhere in modern life including coatings and adhesives in electronics and automobile interior. However, the conventional polyurethane is usually synthesized by a solvent-based process and causes serious environmental problems in use such as emission of volatile organic solvents. In recent years, environment-friendly polyurethane by a waterborne process has received great attention. Waterborne polyurethane adhesives (WPA) for automobile interior require high initial adhesion, heat-resistance, weatherability, and processability. However, it is difficult to satisfy processability during the coating process because of the heterogeneous system of waterborne polyurethane. Therefore, this study was focused on the improvement of processability by control of particle stability of WPA. The results showed that the particle stability of WPA was strongly affected by the nonionomer internal emulsifier.

Preparation of waterborne polyurethane adhesives based on macromolecular-diols containing different diisocyanate

ABSTRACTThree different macromolecular diols were synthesized by the reaction of Poly(1,4-butanediol adipate) diol (PBA) and diisocyanate (Isophorone diisocyanate (IPDI), Hexamethylene diisocyanate (HDI) and Methylene-bis(4-cyclohexylisocyanate)(HMDI)) at the ratio of 2:1. Based on these macromolecular diols, waterborne polyurethane (WPU) adhesives were prepared. The structure and molecular weights of the WPU were characterized by Nuclear magnetic resonance spectroscopy (1H NMR), Fourier Transform Infrared Spectroscopy (FTIR) and Gel permeation chromatography (GPC) respectively. Furthermore, the hydrogen bonding interaction of WPU were analyzed by the deconvolution FTIR spectra. The results showed that the hydrogen bonded NH was increased when carbamate was in the soft segment. The crystallinity of WPU was tested by X-ray diffraction (XRD) and Differential scanning calorimetry (DSC). The results showed that the crystallinity of WPU2 (HDI) and WPU3 (HMDI) were enhanced, especially for WPU2. Meanwhile, the Tg,s as well as the mechanical strength, storage modulus, the contact angle and thermo-stability were increased with the introduced carbamate into soft segment. The T-peel tests of plasticized PVC/WPU/plasticized PVC joints and lap-shear tests of wood/WPU adhesive/wood joints were carried out. The results indicated that the carbamate in the soft segment could significantly enhance the adhesion of WPU at an appropriate activation temperature.

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.

Glycolyzed poly(ethylene terephthalate) waste and castor oil-based polyols for waterborne polyurethane adhesives containing hexamethoxymethyl melamine

Glycolysis of poly(ethylene terephthalate) (PET) waste using different molar ratio of poly(ethylene glycol) (PEG400), was used to produce saturated hydroxyl-functional polyester polyols with castor oil (CO) by transesterification process. The waterborne polyurethane (WBPU) adhesives were synthesized from these saturated polyester polyols, isophorone diisocyanate (IPDI), dimethylolpropionic acid (DMPA), and hexamethoxymethyl melamine (HMMM) as cross-linking agent by a conventional prepolymer process. The glycolyzed polyols and polyester polyos formations were characterized using Fourier transform infrared spectroscopy (FTIR) and the molecular weights were determined using gel permeation chromatography (GPC). The cross-linking reaction between WBPU and HMMM was verified using FTIR and 1H NMR analysis. Thermal properties were investigated by thermogravimetric analysis (TG). Thermal stability of cross-linked WBPU significantly increased with decreasing castor oil content in the process of transesterification to obtain polyester polyol as a soft segment. The T15% and T50% (the temperature where 15 and 50% weight loss occurred) of WBPU increased with the decreasing of castor oil content in the obtained polyester polyols, caused by the steric hindrance of polyester polyol with higher castor oil content, in the process of cross-linking reactions with HMMM. The physico-mechanical properties of WBPU, such as hardness, adhesion test, and gloss of the dried films were also determined considering the effect of participation of HMMM in cross-linking reactions with polyurethane, on coating properties.

Waterborne Polyurethane Adhesives Based on Gelatine-Stabilized AgNPs with Improved Antimicrobial Properties

This work proposes the use of silver nanoparticles (AgNPs) to inhibit the bacterial growth of waterborne polyurethane adhesives. Therefore, AgNPs were synthesized from AgNO3 using a natural polymer like gelatine as a reducing and stabilizing agent. The AgNPs exhibited a strong antimicrobial activity at very low concentrations. The incorporation of gelatine-stabilized AgNPs conferred antimicrobial properties on waterborne polyurethane adhesives without significantly altering their chemical, thermal, and adhesive properties.

Novel Waterborne Polyurethane Adhesives Based on Ag@SiO2 Nanocomposites

In this work, the use of silver-based silica nanocomposites (Ag@SiO2) was proposed to inhibit the microorganism growth of waterborne polyurethane adhesives. For that purpose, colloidal silver nanoparticles were prepared and embedded in a SiO2-based matrix in order to decrease the silver aggregation tendency. The protection of AgNPs with silica was also intended to improve the stability of the adhesive toward metallic particles. Last but not least, Ag@SiO2 provides safer handling of the silver nanoparticles due to their immobilisation within the silica matrix. Colloidal silver was prepared by the Creigthon method using NaBH4 as a reducing agent and polyvinylpyrrolidone (PVP) as a stabilising agent. The coating of the AgNPs by the silica matrix was achieved through a modified Stöber process. The stability of the AgNPs in different amino-based catalysts for the silica matrix synthesis was evaluated in order to successfully obtain silver–silica core-shell nanocomposites. After that, AgNPs and Ag@SiO2 nanocomposites were incorporated in a waterborne polyurethane adhesive and the chemical, thermal adhesion and antimicrobial properties were evaluated.

Synthesis and properties of waterborne polyurethane adhesives: effect of chain extender of ethylene diamine, butanediol, and fluoro-butanediol

Waterborne polyurethane (WBPU) adhesives were prepared using poly(tetramethylene oxide glycol), 4,4’-dicyclohexylmethane diisocyanate (H12MDI), hydrophilic agent dimethylol propionic acid and chain extender of 2,2,3,3-tetrafluoro-1,4-butanediol (TFBD), ethylene diamine (EDA), and 1,4-butanediol. All three chain extenders have been used as single and mixed (different ratio) content during synthesis, and the effect of chain extender and their content to the properties of tensile strength, Young’s modulus, water swelling (%), and adhesive strength was investigated. The adhesive strength value was higher using EDA as a single-chain extender; however, the potentiality of adhesive strength under water was improved using mixed-chain extenders of EDA and TFBD in WBPU adhesives. The maxima potentiality was observed with 6.31 mole% TFBD and 2.10 mole% EDA in WBPU adhesives.

Chemical Functionalization and Dispersion of Carbon Nanofibers in Waterborne Polyurethane Adhesives

Waterborne polyurethane adhesives (WBPU) reinforced with carbon nanofibers (CNFs), to make them also conductive to static electricity, were prepared and their properties were evaluated as a function of content (0.1–1 wt%). The incorporation of carbon nanofibers to waterborne polyurethane adhesives implies a great difficulty because of their tendency to form aggregates, which prevents an efficient dispersion. In this sense, it is necessary to insert functional groups on the surface of the nanofibers to improve their interaction with any polymer. In this research, the surfaces of carbon nanofibers were previously oxygenated by chemical functionalization to enhance their stability in waterborne polyurethane adhesives. The obtained results showed that the chemical treatment used to functionalize the carbon nanofillers was adequate, as well as the experimental procedure carried out for their incorporation into the polyurethane, since stable dispersions were obtained. Moreover, the addition of the nanofibers to the waterborne polyurethanes contributed to improving their rheological and viscoelastic properties, imparting an increase in the viscosity and changes in the crystallisation kinetics.

Effect of Amount of Carbon Nanotubes in Polyurethane Dispersions

AbstractSummary: The possibility of incorporating nanotubes to adhesives opens a new range of innovative solutions, due to their unique structure and properties. In this sense, the objective of this work is the addition of carbon nanotubes (CNTs) to waterborne polyurethane adhesives (WBPU) to improve their rheological, viscoelastic, thermal and mechanical properties and even impart some electrical conductive character to adhesives. Specifically, the stability of the dispersion and the influence of the amount of nanotubes on the properties of the adhesive have been studied.

Effect of Amount of Functionalised Carbon Nanofibres in Polyurethane Dispersions

Waterborne polyurethane (WBPU) adhesives reinforced with carbon nanofibres (CNFs) were prepared, and their properties were evaluated as a function of content (0.1–1 wt%). The incorporation of carbon nanofibres into waterborne polyurethane adhesives presents great difficulty because of their tendency to form aggregates, which prevents an efficient dispersion. It is therefore necessary to introduce functional groups on the surface of the nanofibres to improve their interaction with any polymer. In this research, carbon nanofibres were preoxidised by chemical functionalisation to enhance their stability in waterborne polyurethane adhesives. The results showed that the chemical treatment used to functionalise the carbon nanofillers and the experimental procedure employed to incorporate them into the polyurethane were adequate, as stable dispersions were obtained. Moreover, the addition of nanofibres to the waterborne polyurethanes improved their rheological and viscoelastic properties, resulting in an increase in viscosity and causing changes in the crystallisation kinetics.

Influence of the Chain Extender Nature on Adhesives Properties of Polyurethane Dispersions

Several waterborne polyurethane adhesives containing different chain extenders were prepared by using the acetone process. Concretely, the polyurethane dispersions were synthesized by the prepolymer method based on three chain extenders: two diols and one diamine: 1,4-butanediol, 1,6-hexanediol and hydrazine. The adhesive solutions were characterized by flow rheology, pH measurements, particle size, and solids content. The solid adhesive films were characterized by plate-plate rheology, dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The adhesion properties were measured from T-peel test of leather/polyurethane adhesive/SBR rubber joints. As a result, the chosen chain extender influences significantly the polyurethane synthesized properties, especially determines the crystallinity of the polymer, as well as thermal and adhesive properties. Particularly, the molecular weight of the chain extender determines the structure of the synthesized polyurethanes.

Characterization of Polyurethanes Containing Different Chain Extenders

Several waterborne polyurethane adhesives containing different chain extenders were prepared by using the acetone process. Concretely, the polyurethane dispersions were synthesized by the prepolymer method based on three chain extenders: two diols and one diamine: 1,4-butanediol, 1,6-hexanediol and hydrazine. The adhesive solutions were characterized by flow rheology, pH measurements, particle size and solids content. The solid adhesive films were characterized by plate-plate rheology, dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The adhesion properties were measured from T-peel test of leather/polyurethane adhesive/SBR rubber joints. As a result, the chosen chain extender influences significantly the polyurethane synthesized properties, specially determines the crystallinity of the polymer, as well as thermal and adhesive properties. Particularly, the molecular weight of the chain extender determines the structure of the synthesized polyurethanes.

Influence of the solids content on the properties of waterborne polyurethane dispersions obtained with polycarbonate of hexanediol

Waterborne polyurethane adhesives are an interesting alternative to the current solvent-borne polyurethane adhesives used in the industry. Different aliphatic waterborne polyurethane dispersions (PUDs) with different solids content were synthesised by reacting isophorone diisocyanate (IPDI) with a polycarbonate derived from hexanediol via the acetone method. The PUDs were characterised by Brookfield viscosity, pH, particle size, transmission electron microscopy (TEM) and solids content measurement. The dry polyurethane films were characterised by ATR-IR spectroscopy, plate–plate rheology, differential scanning calorimetry (DSC) and thermal gravimetry (TGA). Their adhesion was evaluated from T-peel tests of flexible PVC/waterborne polyurethane dispersion/flexible PVC joints and single lap-shear tests of aluminium/waterborne polyurethane dispersion/aluminium joints. The PUDs showed bimodal particle size distribution. The mean particle size of the PUDs decreased by increasing their solids content but the particle size distribution of the PUDs increased by decreasing their solids content. As the solids content increased the Brookfield viscosity of the PUDs increased due to lower mean particle size where particle crowding was favoured, the PUD having 44 wt% solids content was an exception (higher particle size but lower polydispersity). On the other hand, the increase in the solids content increased the hard segments content and the degree of phase separation of the polyurethanes. The greater the solids content of the polyurethanes, the lower their glass transition temperatures values and the lower the elastic moduli. Adhesive strength under peel stresses were not affected by the solids content in the polyurethanes but the single lap-shear strength values decreased by increasing the solid contents in the polyurethanes due to lower hard segments content.

Monocomponent Waterborne Polyurethane Adhesives: Influence of the Crosslinking Agent on Their Properties

To improve the properties of the monocomponent waterborne polyurethane (WPU) adhesives, a series of crosslinked WPU were prepared with trifunctional polyester polyol (P210) as crosslinking agent. The crosslinked WPU dispersions and their films were characterized by conventional methods. The adhesion property of the samples was measured from T-peel test of leather/WPU adhesive/leather joints. Compared with the linear one, the crosslinked WPU exhibited low viscosity, small particle size, and low surface tension. For crosslinked films, the thermal stability, water resistance and mechanical properties were remarkably enhanced. The experimental data of T-peel test indicated that the adhesive strength significantly increased to 4.8 KN/m by crosslinking up to the optimum crosslink index of 1.2 and then showed a small decrease with excess.

Properties of Waterborne Polyurethane Adhesives with Aliphatic and Aromatic Diisocyanates

A series of waterborne polyurethane (WBPU) adhesives were prepared with various ratios of aliphatic/aromatic diisocyanates, namely 4,4′-dicyclohexylmethane diisocyanate (H12MDI) as an aliphatic diisocyanate and 4,4′-diphenylmethane diisocyanate (MDI) as an aromatic diisocyanate with poly(tetramethyleneoxideglycol) (PTMG), ethylene diamine (EDA) and dimethylol propionic acid (DMPA). 1H-NMR spectroscopy was utilized to investigate the side reaction at the dispersion step during synthesis of WBPU dispersions with respect to aliphatic, aromatic and mixed diisocyanates. The tensile strength, Young's modulus, elongation at break (%), storage modulus, glass transition temperature and adhesive strength were measured with respect to aliphatic/aromatic diisocyanate contents. The adhesive strength was maximum using mixed diisocyanates containing 25 mol% MDI in WBPU adhesives.

PREPARATION AND CHARACTERIZATION OF WATERBORNE POLYURETHANE AS SHOE ADHESIVES

A series of waterborne polyurethane(WBPU) adhesives for shoes were synthesized by a prepolymer process using dimethylol propionic acid(DMPA) and sucrose as a hydrophilic agent and a cross-linking agent,respectively.Their structures and thermal behaviors were studied by means of FTIR and DSC.Their water swelling,curing time,mechanical properties,e.g.tensile strength,elongation at break and T-peel strength were measured for all samples with different sucrose contents(0～6.82 wt%).The results showed that the sucrose dispersed well as an incorporated state in the polyurethane phase.The curing time of WBPU samples were decreased with increasing sucrose content at the same treating temperature.The water swelling decreased with increasing sucrose content having an optimum sucrose content at 4.13 wt%,and then it increased slightly with further increase of sucrose content.The tensile strength increased from 8.1 MPa to 22.8 MPa,while the elongation at break decreased from 933.5% to 618.7%.The initial peel strength and final peel strength were significantly increased up to an optimum content of sucrose and then decreased slightly with excess sucrose.In addition,it is noted that polyurethane prepolymers more easily remained at an aggregated state during the process of synthesis,and the adhesive strength of the result products decreased when the sucrose content was more than 5.52 wt%.

Influence of the Chemical Structure of Urethane-Based Thickeners on the Properties of Waterborne Polyurethane Adhesives

To analyse the parameters that influence the thickening mechanism of waterborne polyurethane adhesives, different hydrophobically modified ethoxylated polyurethane based thickeners (HEUR) were used. The thickeners were characterized by proton nuclear magnetic resonance (1H-NMR) and gel permeation chromatography (GPC). The thickened adhesive solutions were characterized by flow rheology, pH, particle size measurements, solids content, and confocal microscopy. The thickened solid adhesive films were characterized by ATR-IR spectroscopy, parallel plate rheology, dynamic mechanical thermal analysis (DMTA), and differential scanning calorimetry (DSC). The adhesion was measured by a T-peel test of leather/polyurethane adhesive/SBR rubber joints. The addition of the different HEUR thickeners increased the viscosity of the polyurethane dispersion to different degrees. Furthermore, whereas the un-thickened polyurethane dispersion showed a Newtonian rheological behaviour, a shear-thinning rheological behaviour was observed in the thickened dispersions due to thickener-thickener and polyurethane-thickener interactions. The viscosity of the thickened polyurethane adhesive solutions increased with the degree of hydrophobicity and the molecular weight of the thickener. The addition of different thickeners increased the pH values due to the ionic adsorption, which is one of the interactions that contribute to the thickening mechanism of the polyurethane thickeners, besides hydrogen bonding and van der Waals hydrophobic interactions (micelles). The entanglement of the thickened polyurethane adhesives was studied by confocal microscopy. Although the addition of the thickeners did not affect the thermal properties of the polyurethanes, the T-peel strength of leather/adhesive/SBR rubber joints was influenced by the rheological properties of the thickened adhesives.