Reactive Hot Melt Adhesives Research Articles

Facile synthesis of polyester-polyether block copolyols for the sustainable high-performance polyurethane reactive hot melt adhesives

The presence of polyols with both polyester and polyether structures in polyurethane enhances bonding strength and facilitates easy curing. In this study, polyester-polyether block polyols with varying molecular weights (2500–3500) were synthesized through ring-opening polymerization (ROP) using l-lactide (LA) and ε-Caprolactone (CL). The chemical structure of the polyols was characterized using 1H nuclear magnetic resonance (1H NMR), Fourier transform infrared (FTIR), and gel permeation chromatography (GPC). Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) were employed to examine the crystalline morphology of the polyols. Subsequently, the synthesized polyols were combined with 4,4′-diphenylmethane diisocyanate (MDI) and other additives to prepare polyurethane reactive hot melt adhesives. It was observed that, in PCL-based polyurethane reactive hot melt adhesives, increasing the molecular weight of the polyols resulted in improved crystalline morphology, increased lap shear strength and tensile strength, and enhanced thermal stability. On the other hand, PLA-based polyurethane reactive hot melt adhesives exhibited low bonding strength and lacked practical application value due to the poor toughness of PLA. Interestingly, the bonding strength and tensile strength of PLA-based polyurethane reactive hot melt adhesives improved when physically blended with PCL-based polyurethane reactive hot melt adhesives. These polyols offer a novel approach for utilizing LA and CL in adhesive applications.

Bio-based polyurethane reactive hot-melt adhesives derived from isosorbide-based polyester polyols with different carbon chain lengths

Bio-based isosorbide (ISO), 1,3-propanediol (PDO) and dicarboxylic acids with various carbon chain lengths were employed to synthesize a range of isosorbide-based polyester polyols with a constant molecular weight. Then these polyester polyols were used to prepare polyurethane reactive hot-melt adhesives (PURHMAs). The thermal properties and morphology of polyester polyols were characterized by differential scanning calorimetry (DSC) and polarizing microscope (POM), respectively. The bonding properties of PURHMAs on polycarbonate (PC), iron (Fe) and aluminum (Al) were tested, and Fourier-transform infrared spectroscopy (FTIR) was used to monitor the curing process of the adhesives. Tensile test, hardness test and thermogravimetric analysis were also carried out. The impacts of isosorbide content and the carbon chain length on the properties of both polyester polyols and PURHMAs were studied in this work. The ultimate strength of PURHMAs with a longer carbon chain to PC is higher than 6.74 MPa and the highest can reach 8.04 MPa. Finally, bio-based PURHMAs prepared in this work showed good tensile properties and thermal resistance and have a very promising prospect of being applied to the adhesive industry.

Study on Preparation and Performance of Reactive Polyurethane Hot Melt Adhesives Based on a Polycarbonate Diol and a Polyester Diol

Reactive polyurethane hot melt adhesives (HMPURs) containing a mixture of poly 1,3-propylene sebacate diols (PPSe) and poly 1,6-hexanediol carbonate diols (PHC) as soft segments were prepared to investigate the influence of the relative content of PHC and PPSe on the properties of the HMPURs. The results showed that the HMPURs had excellent thermal stability below 250 °C; when the temperature was above 250 °C but below 360 °C, the HMPURs prepared from PPSe or PHC had better thermal stability than the HMPURs prepared from the mixture. With the increase of PHC content, the melting viscosity and elongation at break (δ) of the HMPURs decreased, while the open time and bond strength of the adhesive on PC substrates increased. When the polycarbonate diol content in the soft segments was higher than 50%, the HMPURs had better hydrolysis resistance than when it was lower.

Reactive polyurethane hot melt adhesives based on polycarbonate and sebacic acid-based polyester polyols

Reactive polyurethane hot melt adhesives (HMPURs) containing a blend of polyester and polycarbonate diols can typically exhibit balanced performance, such as bonding properties, tensile strength, and heat resistance. Two series of HMPURs made from poly 1,4-butylene adipate or sebacic acid (SeA)-based polyester diols with different molecular weights were prepared and investigated. Increasing the molecular weight of the SeA-based polyester diols was found to significantly improve their mechanical properties and lap shear strengths. Moreover, the HMPURs made from SeA-based polyester diol exhibited better performances than those made from poly 1,4-butylene adipate. Also, the HMPURs were more suitable for bonding on PC substrate.

Sustainable Reactive Polyurethane Hot Melt Adhesives Based on Vegetable Polyols for Footwear Industry.

The aim of this work is to develop sustainable reactive polyurethane hot melt adhesives (HMPUR) for footwear applications based on biobased polyols as renewable resources, where ma-croglycol mixtures of polyadipate of 1,4-butanediol, polypropylene and different biobased polyols were employed and further reacted with 4-4′-diphenylmethane diisocyanate. The different reactive polyurethane hot melt adhesives obtained were characterized with different experimental techniques, such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), softening temperature and melting viscosity. Finally, their adhesion properties were measured from T-peel tests on leather/HMPUR adhesives/SBR rubber joints in order to establish the viability of the used biobased polyols and the amount of these polyols that could be added to reactive polyurethane hot melt adhesives satisfactorily to meet the quality requirements of footwear joints. All biobased polyols and percentages added to the polyurethane adhesive formulations successfully met the quality requirements of footwear, being comparable to traditional adhesives currently used in footwear joints in terms of final strength. Therefore, these new sustainable polyurethane adhesives can be considered as suitable and sustainable alternatives to the adhesives commonly used in footwear joints.

Synthesis and properties of reactive polyurethane hot melt adhesive based on a novel phosphorus-nitrogen-containing polyol

A novel phosphorus-nitrogen-contaning polyol (BHAPE) was synthesized from formaldehyde solution, 2, 2'-iminodiethanol and diethly phosphite by typical Kabachnik-Fields reaction. Reactive polyurethane hot melt adhesives with hydrolysis resistance and enhanced flame retardant properties (HMPURs) were prepared from poly (1, 4-butylene adipate), poly (carbonate diol), poly (tetramethylene ether glycol) and BHAPE. The bonding strength, thermal stability, flame retardant performance, mechanical properties and hydrolytic resistance of the HMPURs were studied. The results illustrate that the incorporation of BHAPE for HMPURs could cause a higher thermal stability and more char yield. The melt viscosity, Young's modulus, tensile strength and elongation at break of HMPURs increase with the increase of BHAPE content, and then decrease when the BHAPE content reaches 4 wt%.The optimal content of BHAPE is 4–6wt% and the obtained HMPURs have the limit oxygen index (LOI) of 27.1–31.7% and the higher green strength. Meanwhile, introducing polycarbonate diol to HMPUR can effectively improve its hydrolysis resistance.

Sustainable adhesives and adhesion processes for the footwear industry

The key to sustainable development in the footwear industry through the principles of circular economy lies in taking care of the design, as well as the introduction of innovative and more resource efficient materials and processes to reduce or avoid the use of water, energy, hazardous chemicals and to minimise emissions and waste. In fact, the environmental footprint is already being considered as another requirement of the footwear through eco-design. In this sense, previous studies carried out by INESCOP regarding its environmental impact in terms of carbon footprint showed that 15% of it corresponds to the assembly processes, mainly by adhesive joints, due to their content on organic solvents, hazardous chemicals and polymers from fossil origin. Therefore, this paper focuses on recent developments carried out by INESCOP on more sustainable adhesives and adhesion processes for the upper-to-sole assembly in the footwear manufacturing process, through different approaches. Firstly, bio-based reactive polyurethane hot melt adhesives have been synthesised using polyols from different renewable sources. Secondly, the use of the low-pressure plasma surface treatment to improve the adhesion of polymeric materials used as soling materials was assessed in order to reduce volatile organic compounds emissions, as well as the use of hazardous chemicals for total automation of the bonding process.

Synthesis, characterization and properties of biomass and carbon dioxide derived polyurethane reactive hot-melt adhesives

AbstractPolyurethane reactive hot-melt adhesives (PURHs) are frequently employed in industries; however, there is still a need to develop more sustainable and versatile methodologies to expand the functions and fabrication of these important materials. Renewable feedstock can give PURHs with new functions, and reduce environmental impact. This study focuses on synthesizing PURHs using polyols derived from biomass (plants) and greenhouse gas (CO2) resources. These PURHs were characterized by multiple techniques, including solid-state 13C nuclear magnetic resonance (NMR), a dynamic mechanical analysis (DMA), single-lap adhesive joints strength of stainless steel, and hydrolytic ageing. The PURH film based on biomass poly(tetramethylene ether) glycol (bio-PTMEG) exhibited better water vapor permeability, tensile strength, and adhesive joints properties than PURHs based on cashew nutshell liquid (CNSL) polyester diol and poly(propylene carbonate)-poly(propylene glycol) (PPC-PPG) copolymer diol. The polyols blend of bio-PTMEG with biomass and CO2 based polycarbonate diols respectively provided PURHs films excellent hydrolysis resistance and adhesive strength on single-lap adhesively bonded stainless steel specimens. The work herein demonstrates that various renewable polyols can be employed in a sustainable fashion to optimize the structures and properties of PURHs for important applications.

CO2-based poly (propylene carbonate) with various carbonate linkage content for reactive hot-melt polyurethane adhesives

Reactive hot-melt polyurethane adhesives (RHMPA) are compelling green adhesives without any solvent. However, current RHMPAs are mainly made from non-renewable petroleum-based polyols. Poly (propylene carbonate) (PPC) derived from abundant, cheap and renewable greenhouse gas CO2 is a high-profile green renewable polyol. Here, a series of RHMPAs (PPC-RHMPAs) based on PPC with different carbonate linkage content were prepared. The difference of carbonate linkage content of PPC-RHMPAs was investigated by 1H NMR and FTIR. The effects of carbonate linkage content on the moisture-curing rate, crystallization behavior, thermal stability, mechanical properties and adhesion properties of the resulted PPC-RHMPAs were analyzed and discussed by real-time FTIR, DSC, TGA, tensile and adhesion tests. This work would pave a way for designing high-performance PPC-RHMPAs.

Characterization a polyurethane-based reactive hot melt adhesive for applications in materials

In the present study, we used tensile shear tests, Shore hardness tests, differential scanning calorimetry (DSC), and thermogravimetry (TGA) to characterize a reactive polyurethane-based hot melt adhesive. We also measured contact angles at various temperatures to evaluate the wettability of the adhesive and to determine the optimum temperature range for applications. The adhesive was tested following curing for various times, and the bonding of the adhesive with several materials was investigated to determine whether it has the potential for greater versatility of application. Therefore, we explored new uses of the adhesive, such as in the matrix of a composite with fiberglass. Reactive hot melt adhesives are useful because they provide a certain degree of flexibility to joints, and have high processing speeds, high initial rigidity, and high working temperatures.

Influence of Curing Catalyst on the Properties of Reactive Hot Melt Adhesive

Influence of Curing Catalyst on the Properties of Reactive Hot Melt Adhesive

Bio-polyols synthesized from bio-based 1,3-propanediol and applications on polyurethane reactive hot melt adhesives

Since polyol is one of the major components in the preparation of polyurethane adhesive, bio-based polyols applied in the adhesive can make them sustainable and environmentally friendly. Regarding of these properties, a series of new bio-based aliphatic poly(1,3-propylene dicarboxylate) diols were synthesized by bio-based 1,3-propanediol (bio-PDO) and aliphatic dicarboxylic acids with different chain lengths. These bio-based polyester diols combined with 100% renewably-sourced poly(trimethylene ether) glycol (PO3G) further reacted with 4,4′-diphenylmethane diisocyanate (MDI) to form polyurethane reactive hot melt adhesives (PURHMAs). The thermal and physical properties of sustainable PURHMAs were characterized by differential scanning calorimetry (DSC), X-Ray diffraction (XRD), dynamic mechanical thermal analyzer (DMA) and thermogravimetric analysis (TGA). Finally, the adhesion properties of PURHMAs on four different substrates were measured, in order to investigate the influence of carbon numbers in the repeating unit of bio-based polyester diols on the morphology and adhesive properties of PURHMAs. It was found that with increasing carbon numbers in the repeating unit, the compatibility between the bio-based polyester and PO3G chains in the PURHMAs was enhanced, the open time of PURHMAs became shorter, and the green strength was also improved. The adhesion performance of bio-based PURHMAs on different substrates was tested, and the results showed that all bio-based PURHMAs had good adhesion to PC, nylon 6 and stainless steel substrates. Furthermore, the bio-based PURHMAs also exhibited excellent bonding strength on PC substrates after the bonded PC/PC joints were aged under the condition of hot water or alkaline solution. All these results suggests that the bio-based PURHMAs can be used in automobile applications.

Novel polyurethane reactive hot melt adhesives based on polycarbonate polyols derived from CO2 for the footwear industry

Since raw materials used in polyurethane adhesives come from fossil resources, there is a trend towards renewable alternatives to petroleum. In this sense, the use of carbon dioxide as a feedstock for the chemical industry is an interesting alternative to oil because CO2 is inexpensive and abundant in the atmosphere. A new generation of CO2-based polymers has been recently developed, specifically, polyols, essential components for polyurethane synthesis.This work focused on the synthesis of reactive polyurethane hot melt adhesives (HMPUR) containing polycarbonate polyols derived from CO2 and 4,4′-diphenylmethane diisocyanate (MDI). The sustainable polyurethane adhesives derived from carbon dioxide were characterised by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Finally, the adhesion properties were measured from a T-peel test on leather/polyurethane adhesive/SBR rubber joints, in order to establish the amount of CO2-based polycarbonate polyol that could be added to reactive polyurethane hot melt adhesives satisfactorily to meet the quality requirements of footwear joints.All percentages of CO2-based polyol added to polyurethane adhesives meet successfully the quality requirements of footwear, being comparable to conventional adhesives used currently in shoe joints both in terms of green and final strength, and after high temperature/humidity conditions and hydrolysis tests. Therefore, this new generation of sustainable polyurethane adhesives could replace the adhesives commonly used in shoe joints.

The Properties of Reactive Hot Melt Polyurethane Adhesives: Effects of Molecular Weight and Reactive Organoclay

We studied the affect of molecular weight on the adhesion properties of reactive hot melt adhesive (RHA), which has polyurethane prepolymer as its major component. The RHAs that were prepared by the two-shot method and were of a higher average molecular weight showed improved initial bond strength development compared to that of RHAs prepared by the one shot method but with the same recipe. However, the viscosity of the RHA was increased by this method, which reduced the cross-linking in the cured RHA. This was confirmed by its deteriorated tensile properties and increased tan δ value. The reactive organoclay, Cloisite 30B, also improved the initial bond strength development and raised the viscosity of the RHA, thereby reducing cross-linking in the cured RHA.

The products for extremely short processing cycles

Every day, bonded or laminated interior components for automotive applications, like ceiling liners, dashboards or door and side panelling, are subject to extreme stress factors. 2K PUR adhesives on solvent basis, 2K PUR dispersions or reactive polyurethane hot melt adhesives (PUR-HM), meet these challenges. Still, there is some potential for improvement — and PUR hot melt adhesives which have been newly introduced to the market provide the answer.

The properties of reactive hot melt polyurethane adhesives modified with novel thermoplastic polyurethanes

AbstractA reactive hot melt adhesive (RHMA) consisting of thermoplastic polyurethane (TPU) was modified with sodium montmorillonite (Na‐MMT) intercalated with poly(ethylene glycol) (PEG), and their effects on the adhesion, rheological, and mechanical properties of the RHMA were examined. The Na‐MMT intercalated with PEG (Na‐MMT/PEG) effectively enhanced the initial bond strength development of the RHMA, although the amounts of Na‐MMT/PEG in the RHMA were less than 0.2%. The increase of the complex viscosity and pseudo‐solid like behavior observed at low shear rate indicates that there are intimate interactions between the RHMA molecules and Na‐MMT/PEG. The improved modulus and tensile strength of the cured RHMA film in the presence of Na‐MMT/PEG demonstrates that Na‐MMT/PEG effectively reinforced the RHMA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Reactive hot-melt adhesives for better structural bonding

Reactive hot-melt adhesives for better structural bonding

Properties of Reactive Hot Melt Adhesives Modified by Polyurethane Containing PEG Segment Intercalated in Sodium Montmorillonite

An additive of reactive hot melt adhesive (RHMA), thermoplastic polyurethanes (TPUs) was modified with neat sodium montmorillonite (Na-MMT) or Na-MMT intercalated with poly(ethylene glycol) (PEG), and their effects on the adhesion, rheological, and mechanical properties of RHMA were examined. The neat Na-MMT or Na-MMT intercalated with PEG (Na-MMT/PEG) effectively reduced the set time of RHMA, although the contents of neat Na-MMT or Na-MMT/PEG were less than 0.2 %. The increase of complex viscosity and pseudo-solid like behavior observed at low shear rate indicated that there were intimate interactions between RHMA molecules and neat Na-MMT or Na-MMT/PEG.

Structural investigations of polypropylene glycol (PPG) and isophorone diisocyanate (IPDI) based polyurethane prepolymer by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)-mass spectrometry

The wide application of polyurethane (PU) prepolymers in the reactive hot melt adhesives, sealant and coating sector has made it necessary to understand the changes occurring during polymerization. NCO terminated PU of polypropylene glycol (PPG-2000) and isophorone diisocyanate (IPDI) with NCO/OH ratio 2:1 were prepared. The reaction was continued up to 111 h and the prepolymer obtained at different reaction times were partly removed from the reaction kettle and end-capped with methanol. The end-capped samples were subjected to MALDI-TOF-mass spectral investigation. The peaks at different reaction times in the MALDI-TOF-mass spectra were identified as different PPG homologues. These results suggest that initially the reaction produces monourethane, which subsequently convert to diurethane during the course of reaction.

Sodium montmorillonite intercalated with poly(ethylene glycol): a modifier of reactive hot-melt polyurethane adhesive

We have examined the effects of a sodium montmorillonite (Na-MMT) intercalated with poly(ethylene glycol) (PEG) on the properties of a reactive hot melt adhesive (RHA) based on polyurethane pre-polymer with terminal isocyanate groups. The bond strengths of the RHA, from the initial to final time period after application, were enhanced and the set time was reduced by the addition of 1–3 phr Na-MMT intercalated with PEG (Na-MMT/PEG). The modifier increased the viscosity and a pseudo-solid-like behavior at low shear rates when subjected to a dynamic shear stress. Further, both the tensile modulus and tensile strength of cured RHA films were improved by the reinforcing effect of Na-MMT. The X-ray diffraction pattern of RHA showed that the gallery of Na-MMT was intercalated with PEG segment.