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Rheology, mechanical properties and peel adhesion of hot-melt adhesive based on thermoplastic polyurethane/nanosilica
This research focuses on synthesizing two types of polyurethanes (PUs): one with saturated C–C bonds (SPU) and another with unsaturated CC bonds (UPU), primarily in the hard segment. Both types of PUs underwent thermal aging for 30 days at 150°C in an air atmosphere to investigate the influence of unsaturation on their thermal degradation. The samples, both before and after aging, were characterized using FT‐IR, XRD, TGA, DSC, mechanical testing, and SEM. Additionally, the percentage of weight loss was measured. Similar changes were observed in both SPU and UPU after thermal aging. Thermal degradation resulted in mass losses of approximately 5% for SPU and 10% for UPU, accompanied by chemical alterations in the PUs, as evidenced by FT‐IR. Mechanical testing revealed a decline in performance for both materials, with notable reductions in yield strength and elongation at break. UPU exhibited a more pronounced degradation in mechanical properties compared to SPU. SEM analysis further confirmed surface degradation in both materials. Among the two PUs, UPU demonstrated higher susceptibility to thermal degradation. This study provides valuable insights into how the unsaturation in diols or polyols used in PU synthesis influences thermal degradation and the resulting changes in material properties. The findings also highlight the potential performance implications for SPU and UPU when exposed to temperatures exceeding their processing or operational limits.
This investigation reports the preparation and properties of thermoplastic polyurethane/silica nanocomposite prepared via melt mixing process. In this case, nanosilica at different loading was mixed with a polyester-based thermoplastic polyurethane (TPU). The dispersion of nanofiller was studied by the SEM and TEM analyses. The nanocomposite with optimal dispersion of nanofiller has better filler-polymer interaction that has been confirmed by the FT-IR study. TPU with 1 phr of nanosilica loading showed better tensile properties. DSC study revealed that incorporation of fumed silica in the TPU matrix does not substantially affect the refinement of TPU crystallite, and thus resulted in an insignificant change in glass transition temperature (Tg) and crystalline melting temperature of the nanocomposite. TGA study also confirmed enhanced onset degradation temperature and maximum degradation temperature (Tmax) for optimal nanosilica composite. The final degradation temperature and char content also increased with an increase in fumed silica content. Water contact angle (WCA) study revealed that hydrophilicity of the nanocomposite increased with the incorporation of fumed silica.
A series of hot-melt adhesives (HMAs) were made from poly(ethylene-co-vinyl acetate) (EVA) and a glycerol ester of partially hydrogenated rosin (Staybelite Ester 10, SE10) in various ratios. A content of 70 parts of SE10 per hundred parts (phr) of EVA showed a maximal peel strength. The effect of decreasing the rubbery plateau G’ value and increasing the glass transition temperature while increasing the SE10 content seems evident in the peel strength study. The trend also showed that the tackifier became less effective when the Tg’s of the adhesive mixture were higher than a limit temperature (i.e., 15°C).
With 70 phr of SE10, the compatibility of the adhesive blend was further improved by adding 10 phr of wax, and the recipe displayed an even higher peel strength value. The presence of wax leads to ultrahigh cohesive strength, which is related to the rapid increase in crystallinity of the adhesive mixture. Formulating with a larger amount of wax worsens the peel strength, which may be explained by the formation of a weak boundary layer of the adhesive mixture on the surface of the adhesive blend.
Polyurethane/graphene nanocomposites were synthesized using commercial thermoplastic polyurethane (TPU, Apilon 52DE55), and two types of graphene derivatives: graphene nanoplatelets (GNP) and reduced graphene oxide (RGO). Fourier Transformation Infrared Spectroscopy Fourier Transformation Infrared Spectroscopy (FTIR) spectroscopy, TEM, and SEM microscopy and XRD techniques were used to chemically and structurally characterize GNP and RGO nanofillers. The properties of the new TPU nanocomposite materials were studied using thermal analysis techniques (Dynamical Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TG)) to describe the influence of graphene nanofillers on polyurethane matrix. Our investigation describes the comparison of two types of graphene derivatives, commercial one (GNP) and synthesized (RGO) on thermoplastic polyurethanes. These nanofillers provides opportunities to achieve compatibility with the TPU matrix. The property enhancements are attributed commonly to high aspect ratio of graphene nanoplatelets and filler–polymer interactions at the interface. The obtained nanocomposites exhibit higher thermal and mechanical properties due to the good dispersion of both nanofillers into TPU matrix. It was found that the addition of 2 wt % of the nanofiller could lead to a significant reinforcement effect on the TPU matrix. Also, with high content of nanofiller (GNP and RGO), the Payne effect was observed.
Nanofilled polymeric matrices have demonstrated remarkable mechanical, electrical, and thermal properties. In this article we review the processing of carbon nanotube, graphene, and clay montmorillonite platelet as potential nanofillers to form nanocomposites. The various functionalization techniques of modifying the nanofillers to enable interaction with polymers are summarized. The importance of filler dispersion in the polymeric matrix is highlighted. Finally, the challenges and future outlook for nanofilled polymeric composites are presented.
Polyurethane adhesive is containing isocyanate and urethane groups in the molecular bonds, a kind of adhesive has high polarity and lively type. By adjusting the raw materials and formulations can be perpared to meet the requirement of the raw product between different materials bonding. In this paper, the experiments used poly-1,4-butylene adipate glycol (PBA) as soft segment materials and 4, 4’-diphenylmethane diisocyanate as hard segment materials, and used 1,4-butylene glycol as chain extender. What’s more, the experiment adopt rosin resin, phenylethylene and petroleum resin as polyurethane tackifier, we can composed to polyurethane polymers in certain conditions. By changing the type and amount of tackifier ,we can get different polymers, after that from initial strength, final strength, softening temperature and melt viscosity do a comparative experiment with the polyurethane hot melt adhesive of books binding. The results show that proper selection and addition of petroleum resin can meet the requirement of bond property of polyurethane hot melt adhesive which used in books binding, and it has the advantages of low cost ,energy conservation and environmental protection ,which makes it has a good application prospect.
The thermoplastic polyurethane elastomer (TPU) was firstly synthesized by using polybutylene adipate (PBA) as soft segments, methane-4-4’-diisocyanate(MDI) and 1,4–butanediol(BDO) as hard segments. The polyurethane hot-melt adhesive was then prepared by adding the tackifying resin, filler and other auxiliaries into the TPU matrix. The structure of the synthetic products was characterized by Infrared Spectrum and the thermal properties and microstructure of polyurethane hot-melt adhesive was tested by the thermogravimetric(TG) and the scanning electron microscopy(SEM), respectively. The results showed that the thermoplastic polyurethane elastomer had the expected structure, the shear strength of polyurethane hot-melt adhesive increased with the pentaerythritol abietate content increasing when the addition of the pentaerythritol abietate is less than 20 wt%, and decreased with the content of CaCO3 filler and petroleum resin increasing, respectively; the thermal stability was improved, and the char yields of the polyurethane blends increased with adding the filler CaCO3. When the molar ratio of PBA:MDI:BDO was 1:2:1, the addition of pentaerythritol abietate and filler CaCO3 was 20 wt% and 30 wt%, the comprehensive performance of PU hot-melt adhesive was better and the shear strength was 7.37 MPa.
Carbon nanotube buckypaper/thermoplastic polyurethane elastomer composites were successfully fabricated. At certain polyurethane contents, the composites exhibited simultaneous improvements in stiffness (up to 6 GPa), strength (up to 120 MPa), ductility (up to 30%) and toughness (up to 36 MJ/m3). The measured elastic modulus of the composites could be predicted by Mori–Tanaka model. The possible reinforcing mechanisms were discussed by Raman spectroscopy and SEM fractography. The results revealed that ductile polymers are very promising matrix in balancing the key mechanical properties of buckypaper, which are beyond the commonly used brittle thermosettings, e.g. epoxy resin.
Hot-Melt Adhesives (HMAs) are typically used in applications where instant sealing is critically required. HMAs are generally preferred for those applications where processing speed is critical. These materials are widely used in various engineering applications, mainly as sealants in leakages and crack filling of walls and roofs. The industrial use of HMAs is most common in glassware and automobiles for gluing glasses in buildings and bonding heavy motor parts. The formulation of HMAs contains a polymer of suitable nature that makes the base for a strong adhesive, and waxes are added to increase the settling time of adhesive. The tackifiers are used to dilute the polymer to adjust the Glass Transition Temperature (T g ) and to reduce the viscosity for proper flow of hot-melt. This review intends to comprehensively discuss the preparation and formulations of HMAs using various polymer matrices, along with their applications and mechanics. The designing of green HMAs has been discussed in the literature and have been promoted over conventional solvent-based HMAs due to their functionality without Volatile Organic Compounds (VOCs). Various measures, challenges, and resolutions for making hazard-free HMAs have been discussed in the present review.
This article studies the migration of MOAH from hot melt adhesives used in multilayer laminates into food simulants. First, the initial concentration of a group of compounds selected as MOAH markers in several adhesives was determined by headspace solid phase microextraction coupled to gas chromatography mass spectrometry (HS-SPME-GC-MS), using the previously optimised method. Then, the migration of the MOAH fraction
and MOAH markers from the laminates was studied. The MOAH fraction was analysed by gas chromatography with flame ionisation detection (GC-FID), and the MOAH markers were analysed by HS-SPME-GC-MS. Twelve MOAH markers were detected, and their initial concentrations were between 0.46 and 33.8 μg g-1. Only eight were identified after migration, ranging between 0.62 and 21.33 μg dm-2, with a migration percentage of
12–75%. The fraction of MOAH that migrated eluted mainly in the C16-C25 range and reached concentrations of 19.65 μg dm-2 from the laminate.
Hot‐Melt Adhesives (HMAs) are typically used in applications where instant sealing is critically required. HMAs are generally preferred for those applications where processing speed is critical. These materials are widely used in various engineering applications, mainly as sealants in leakages and crack filling of walls and roofs. The industrial use of HMAs is most common in glassware and automobiles for gluing glasses in buildings and bonding heavy motor parts. The formulation of HMAs contains a polymer of suitable nature that makes the base for a strong adhesive, and waxes are added to increase the settling time of adhesive. The tackifiers are used to dilute the polymer to adjust the Glass Transition Temperature (T g ) and to reduce the viscosity for proper flow of hot‐melt. This review intends to comprehensively discuss the preparation and formulations of HMAs using various polymer matrices, along with their applications and mechanics. The designing of green HMAs has been discussed in the literature and have been promoted over conventional solvent‐based HMAs due to their functionality without Volatile Organic Compounds (VOCs). Various measures, challenges, and resolutions for making hazard‐free HMAs have been discussed in the present review.
Polycarbonate-based thermoplastic polyurethane elastomers (PCD-TPUs) were synthesized from polyhexamethylene carbonate diol, 4,4-diphenylmethane diisocyanate and 1,4 butanediol, intended for adhesive applications. The chemical structure, thermal transition temperature, phase separation morphology, mechanical properties, and adhesion properties were studied to elucidate the structure-properties relationship of PCD-TPUs as a function of hard segment content. The phase separation behavior was described as a shift of the glass transition temperature and the dimension size of the hard domain. It was found that the higher hard segment fraction led to a lower degree of phase separation as well as a reduction in tensile strength and elongation at break. The hydrogen bonding characteristic of PCD-TPUs was investigated by FTIR. The presence of free hydrogen bonded PCD-TPUs benefits the higher peel strength since it promotes hydrogen bonding interaction with the substrate. The peel strength was obtained from PCD-TPUs/stainless steel joint. The adhesion properties of the adhesive system were strongly influenced by the soft segment. These results can establish the possibility of designing new formulations for hot melt adhesive.
Thermoplastic polyurethane elastomers (TPUs) have been intensively used as hot-melt adhesives (HMAs) due to their adherence ability that can be applied on hard surfaces. To overcome their drawbacks, such as low peel strength and deformation, the performance improvement of the TPUs-HMAs has become a challenging issue. In this study, the enhancement properties of the TPUs-HMAs were achieved from the copolymerization of a soft-segment technique. Two types of polycarbonate diols (PCDs) were utilized for the TPU production as a co-diol of the soft segment. The properties and phase behaviour of the TPUs with various ratios of copolymerized soft segment were analysed. The compatibility between the different types of the PCDs is defined by the concentration of the hydrogen bonding interaction between the hard and soft phases and the dimensions of the hard domains. The homogeneous dispersion of the hard domains in the soft phase promotes better stress transfer enhancing the mechanical properties and adhesion properties. The peel strength is measured between the TPUs/stainless steel joint, in which the highest value is accomplished with the formulation of 60:40 wt% of copolymerized soft segment, which is associated with the superior mechanical strength and the optimum compatible properties of the soft segment.
Traditional hot melt adhesives are thermoplastic resins with non-covalent hydrogen bonds. In this letter, a polyurethane hot melt adhesive (CDI-PUR-DA) was synthesized via introducing thermally reversible covalent Diels-Alder adducts into the polyurethane main chain. Results from hydrogen nuclear magnetic resonance (NMR) analysis and an assessment of rheological properties demonstrated that CDI-PUR-DA exhibited a much lower viscosity than a traditional hot melt adhesive. The viscosity of the polyurethane decreased to 4 Pa.s at 110 °C due to rupture of Diels-Alder adducts. However, the viscosity returned to its initial value on cooling due to the regeneration of the Diels-Alder adducts. This approach provides a new method for preparing hot melt adhesives.
Polymeric multilayer films are widely used in food packaging due to their versatility. However, there are still some properties that might be improved, such as gas and vapor barrier behaviors. The incorporation of boron nitride into polymer matrixes is emerging as a potential method for the improvement of barrier properties due to its lamellar structure. In this context, our work investigates the addition of boron nitride into a bicomponent reactive polyurethane (PU), which could be used as an adhesive and improve the barrier layer. This material could be used as an alternative to aluminum foil in food packaging. Different concentrations of two different sizes of boron nitride (BN) particles were added to the PU adhesive: micro-structured boron nitride (BNm) and nano-structured boron nitride (BNn). The aim was to investigate the influence on the barrier properties against moisture and the peeling resistance. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) were performed to characterize the boron nitride samples. The effect of BNm or BNn addition on the glass transition of the nanocomposites was investigated by differential scanning calorimetry (DSC). Barrier properties were measured by a water vapor permeation test and the practical adhesion of laminates with BN/PU adhesives was characterized using peeling tests. The nanocomposites achieved reduction in water vapor permeance of up to 50% and a 37% increase in mechanical adhesion properties compared to the PU adhesive. The results revealed the high potential of boron nitride/PU adhesives for food packaging applications.
Aerostat and airship are lighter-than-air (LTA) systems that are mainly used for
defense applications such as military surveillance, detecting aerial threats, etc. and
also for many other purposes. Significant challenges are faced in developing materials
for LTA systems, especially for stratospheric airships, which require balancing
all the required properties. The material should be lightweight, strong, flexible
at low temperature, capable of containing helium gas for a long time, and weather
resistant (i.e., provides protection from intense UV rays, ozone, etc.) and should
provide a long service life. Generally, multilayered coated or laminated fabrics are
used to fulfill all the requirements for this particular application, where a specific
layer executes a specific functionality.
This chapter discusses the basic structure of a multilayered envelope for airship
or aerostat, requirements for each layer, challenges, and different potential
materials (polymers, fibers, and fabrics) for different layers. The case studies of
different coated or laminated fabrics developed by leading competitors that prepare
LTA systems have also been included. It also highlights the potentiality of
advance polymeric nanocomposites, especially polyurethane nanocomposites, for
this particular application. The future possibilities of extensive usage of polymer
nanocomposites and their challenges have also been discussed. Finally, the different
models that have been developed by researchers for predicting the performance
and service life of coated/laminated envelopes of an aerostat/airship have
also been explored.
Graphene nanoplatelets with different surface functional groups and polarity were prepared by Hummer's method and electrochemical exfoliation of graphite in two aqueous acids. The XRD, FTIR and sedimentation tests performed to characterize the polarity of the prepared graphenes. The highest polarity was associated with the sample prepared by Hummer's method and the sample synthesized by electrochemical exfoliation in nitric acid medium showed the moderate polarity. Meanwhile, the sample prepared in sulfuric acid medium showed the lowest polarity. Then thermoplastic polyurethane (TPU)/graphene nanocomposite films were fabricated with solvent exchange method. While the dispersion state and interaction of graphene/segmented polymer in solution state were evaluated with rheological measurements, optical microscope images illustrated the well dispersion of more polar graphene in TPU nanocomposite film. Moreover, the effect of graphene polarity on the phase separation and formation of hard domains with crystalline structure was extensively discussed based on DSC test results. The changes in phase separation between hard and soft segments and the formation of hard domains with specific structures greatly affected the mechanical properties of final nanocomposite films. The electrical conductivity of TPU/graphene nanocomposite film showed the role of graphene polarity nanoplatelets on the development of the conductive network in TPU matrix.
The commonly used fillers for nanocomposites are nanoclay, nano-TiO2, etc. The fillers affect the morphology and properties. This chapter deals with the influence of spherical fillers like nanoparticles, BaSO4, SiO2, etc., on the properties of polyurethane nanocomposites in general.
Thermoplastic polyurethane (TPU) nanohybrids have been prepared through melt extrusion using ester type PU and different concentrations of Indian origin organically modified nanoclay as filler. The level of dispersion of nanoclay in TPU is found to be good and considerable intercalation occurs due to strong interaction between polymer matrix and filler. The interaction is shown through spectroscopic measurement from the shifting of peak position in FTIR and UV–vis. absorption spectra. Nanoclay induces crystallization in polymer while the blob size, as measured through small angle neutron scattering, decreases in nanohybrid (1.5 nm) as compared to pure TPU (1.7 nm) obtained after fitting the initial data point to Debye-Bueche model. Mechanical responses are much superior in nanohybrid as compared to pure TPU and stiffness values continue to increase with nanoclay concentration while the toughness reach ata maximum value at an optimum concentration of 4 wt% of nanoclay. Uniaxial stretching lead to the crystallization of segments and ordering of hard segments as verified through sharp melting points in stretched TPU vis-à-vis predominant amorphous nature before stretching. Nanohybrid membranes are prepared to investigate the gas permeation across the membranes and very high gas barrier of nanohybrid (449 Barrer) is found as opposed to pure TPU barrier of 169 Barrer. Critical assessment of permeability is performed in presence of nanoclay in different concentrations with a plausible mechanism of gas barrier.
Nanocomposites based on thermoplastic polyurethane (TPU) and graphene-based materials such as graphene oxide (GO) and reduced graphene oxide (RGO) was synthesized by in-situ solution polymerization technique. The effect of structural differences between GO and RGO in the thermo-mechanical and surface properties of TPU at ultralow concentration was the foremost aspiration of this work. TPU/GO nanocomposites exhibited superior mechanical properties compared to TPU/RGO nanocomposites at very low loading. With the incorporation of 0.10 wt% of GO, the resultant nanocomposites showed 280% increase in tensile strength and 410% increase in toughness. Interestingly, the elongation at break for nanocomposites increased from 588% for pristine TPU to 1006% for TPU/GO-0.10. Property improvement of RGO filled nanocomposite was not so prominent as compared to GO filled nanocomposites. Thermal stability of the nanocomposites as examined by thermogravimetric analysis (TGA) depicted a 12 °C increase in thermal stability for 0.2 wt% GO filled nanocomposite whereas the same for RGO filled nanocomposite was only 6 °C. Contact angle study revealed that the RGO filled nanocomposites were becoming more hydrophobic whereas GO filled nanocomposites films showed the opposite trend.
The effects of nanosilica type and its content on microstructure, mechanical properties, and rheology of thermoplastic polyurethane (TPU) nanocomposites were investigated. Three different types of silica which included: unmodified (Si-Un) and commercially modified with octylsilane (Si-OS) and polydimethylsiloxane (Si-PDMS) with 5, 10, and 15 wt% of all fillers, were prepared by solution casting method. Scanning electron microscopy (SEM) showed that surface treatment of nanosilica with OS and PDMS reduced the aggregation of particles and improved their dispersion at microlevel. The effect of adding nanoparticles on microdomain morphology of TPU was studied by transmission electron microscopy (TEM), infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The results demonstrated a relatively good interaction between the hard and soft segments in the presence of treated nanosilica that hindered the crystallization of hard segments in TPU. Thermogravimetric analysis (TGA) and tensile test showed that nanocomposites with treated nanosilica have better thermal stability and mechanical properties. The dynamic rheological studies indicated that nanocomposites containing Si-OS and Si-PDMS (with better dispersion and higher interface between the soft and hard domains in TPU) have improved viscoelastic properties in comparison with nanocomposites with untreated silica. In this study, dynamic frequency sweep data were correlated by a generalized Maxwell model and found that elastic constants of TPU chains were improved in the presence of modified silica nanoparticles.
Comparing to the defect of weakness impact resistance of epoxy resin based electrical conductive adhesives (ECAs), flexible conductive adhesives (FCAs) could be used in flexible device electronic packaging. Carbon nanotubes (CNTs) have good properties, which make them to be ideal fillers. In this study, CNTs were used as one-dimensional conductive scaffolds to construct effective networks among the TPU polymer in ECAs. The electrical conductivity and tensile strength improved with the CNT content increased from 0 to 10.0 wt%. In addition, the resistance only changed a little within a certain strain. Under the same strain, the change of R/R0 for the samples with high CNT content is smaller than that of the samples with low CNT content after first cycle. The development of highly conductive, flexible, and low cost ECAs will allow them to be widely used in flexible electronic devices packaging in the future.
Adhesion is among the oldest technologies known to mankind, but the technology of adhesives began to boom with the developments in chemistry in the early 1900s. The last few years have seen tremendous progress in the performance of adhesives, allowing two pieces to be connected inseparably. Modern adhesives perform so well that more sophisticated joining methods, e.g. welding, can often be replaced by adhesion, meaning that adhesives have found new areas of application. This book allows readers to quickly gain an overview of the adhesives available and to select the best adhesive for each purpose.
In the present study, three thermoplastic polyurethanes (TPUs) based on poly(tetramethylene glycol) (PTMG) and poly(butylene adipate) (PBA) as polyols as well as their nanocomposites containing graphene oxide GO (0.3–1%) were prepared. TPUs had Tgs and Tms values in the range of −62.5 to −21.6°C and 5 to 10.8°C, respectively, increasing with enhancing PBA content in their formulations. Increasing of PBA moieties in TPUs resulted in higher crystallinity, elastic modulus and tensile strength values, while elongation at break and Helium permeability were decreased. Incorporation of GO into the TPUs improved crystallinity, mechanical properties and gas barrier values.
Hot-melt adhesives facilitate fast production processes because the adhesives set simply by cooling. Formulations contain polymers to provide strength and hot tack (resistance to separation while adhesive is hot), and tackifiers and/or oils to dilute the polymer entanglement network, adjust the glass-transition temperature, lower the viscosity, and improve wet-out (molecular contact of the adhesive with the substrate over the entire bonding area). Some adhesives also contain waxes to speed setting, lower viscosity, and improve heat resistance. Obtaining adequate strength and heat resistance from nonreactive hot melts requires that some component of the hot melt separate out into a dispersed but interconnected hard-phase network upon cooling. The hard phases are commonly either glassy styrene domains (for adhesives based on styrenic block copolymers) or organic crystallites (for adhesives based on waxes, olefinic copolymers, or ethylene copolymers). This article will describe first the material properties relevant to the processing and performance of hot-melt adhesives, then the chemistry and function of the specific raw materials used in hot melts, and will conclude with illustrative application examples and corresponding formulations.
Three thermoplastic polyurethanes (TPUs) containing different hard/soft (h/s) segment ratios (1.05-1.4) were prepared using the prepolymer method. MDI (diphenylmethane-4,4′diisocyanate) and polyadipate of 1,4-butanediol (M w = 2440) were allowed to react to produce the prepolymer. To provide the polyurethanes with high immediate adhesion to different substrates, a rosin + 1,4-butanediol mixture (1 : 1 equivalent%) was used as chain extender (TPU-Rs). These TPU-Rs had two types of hard segments: (i) Urethane hard segments, produced by reaction of the isocyanate and the 1,4-butanediol, and (ii) Urethan-amide hard segments, produced by reaction of the isocyanate and the carboxylic acid functionality of the rosin. The TPUs and TPU-Rs were characterized using FTIR spectroscopy, gel permeation chromatography, differential scanning calorimetry, stress-controlled plate-plate rheology, stress-strain measurements, and Brookfield viscosity. The TPUs and TPU-Rs were used as raw materials to prepare solvent-based polyurethane adhesives, the adhesion properties of which were obtained from T-peel tests on PVC/polyurethane adhesive/PVC joints. The addition of rosin as an internal tackifier increased the average molecular weight, more markedly in the TPU-Rs containing higher hard/soft segment ratios, but the elastic and viscous moduli decreased. An increase in the hard/soft segment ratio of the TPU-Rs retarded the kinetics of crystallization (which was determined by the soft segment content in the polyurethane), and increased the immediate T-peel strength in PVC/polyurethane adhesive/PVC joints (which was determined by the urethan-amide hard segments). Furthermore, addition of rosin to the polyurethanes decreased the final adhesion, although always reasonably high peel strength values were obtained.
Fumed silicas of different specific surface area (90-380 m/g) were added to a thermoplastic polyurethane (PU) solution. After solvent removal, solid fumed silica-PU composites were obtained. The viscoelastic properties of PU were improved by adding fumed silica and only a solid-like behavior in PU-fumed silica composites was obtained. The increase in the specific surface area of the fumed silica up to 200 m / g increased the moduli of the composites. Fumed silica-PU interactions were responsible for the improved rheological properties of the composites. The activation energies for viscous flow of the composites were 14-16 kcal/mol and increased as the specific surface area of fumed silica increased. The glass transition temperature (obtained from DMTA and DSC experiments) and the crystallization rate of fumed silica-PU composites decreased compared with PU and also decreased with increasing surface area of the fumed silica. The contact angle values were similar in all the composites and the strength of PVC/fumed silica-PU composite joints was not affected by the specific surface area of the fumed silica.
MDI (diphenylmethane-4,4′-diisocyanate) and different mixtures of rosin acid and polyadipate of 1,4-butanediol (Mw=2400) (5–20 equivalent % with respect to the equivalents of OH groups in the macroglycol) were reacted to produce a urethane prepolymer; 1,4-butanediol was added as chain extender. The specific feature of this manufacturing procedure was the use of rosin acid as an internal tackifier in thermoplastic polyurethanes (TPUs), to provide high immediate adhesion to PVC. The TPUs obtained were characterized using gel permeation chromatography, FTIR and NMR-1H spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis and plate–plate stress-controlled rheology. The TPUs were used as raw materials to prepare solvent-based polyurethane adhesives, whose adhesion properties were obtained from T-peel tests of solvent-wiped PVC/TPU adhesive joints. The increase in the amount of rosin acid in the prepolymer led to an increase in average molecular weight and the viscosity of TPU solutions, improved rheological properties, reduced crystallinity and slower kinetic of crystallization. On the other hand, the immediate T-peel strength and the ageing resistance of PVC/TPU joints were improved. The carboxylic acid functionality in the rosin structure reacted with the isocyanate to produce imide-urea moieties that were responsible for the improved properties of the TPUs containing rosin acid as an internal tackifier.
Four silicas, two fumed (one hydrophilic and one hydrophobic) and two precipitated silicas (one hydrophilic and one hydrophobic), were added to a thermoplastic polyurethane (PU). The rheological, mechanical and adhesion properties of the PU–silica composites were considered in this study. In general, the addition of silica increased the viscosity, the storage and loss moduli of the PU–silica composites in solution but only the hydrophilic fumed silica imparted pseudoplasticity and thixotropy. The rheological and mechanical properties imparted by adding fumed silicas to PU were always more important than for precipitated silicas. Interactions between the hydrophilic fumed silica, the polyurethane and/or the solvent seemed to be responsible for the improved rheological properties of the composites. Addition of silica did not modify the glass transition temperature but increased the softening temperature of PU composites. On the other hand, the immediate (green) T-peel strength of roughened or (roughened + chlorinated with 2wt% trichloroisocyanuric acid solutions in 2-butanone) styrene–butadiene rubber/PU composite joints was greatly improved if the PU contained silica, mainly fumed silicas irrespective of their hydrophilic or hydrophobic nature. Similar T-peel strength, 72h after bond formation was found in the joints produced with PU composites with and without silica.
Two series of thin films of polyether-based polyurethane–silica nanocomposites having hard segment content of 51% and 34% and different concentrations of SiO2 nanoparticles (0, 0.5, 1.0 and 3.0vol.%) have been prepared. Infrared linear dichroic (LDIR) ratio, mechanical and differential scanning calorimetry (DSC) measurements were performed in order to determine the influence of hydrogen bonding on their mechanical and thermal properties. The degree of phase separation (DPS) and orientational functions in dependence on strain were calculated from the polarized IR spectra. The presence of silica nanoparticles gives rise to significant differences in the mechanical (stress–strain) properties of the nanocomposites with regard to the pure polymer. The nanocomposite thin films with lower hard segment content (HSC) displayed decreased stiffness and tensile and increased elongation at break in comparison to the nanocomposites with higher HSC. There was no distinctive influence of nanoparticles on the glass transition temperatures of soft segments. Nanosilica significantly affected the melting behavior of the hard phase only in samples with higher HSC.
In this article, the influence of fumed silica nanofiller on the structure and properties of segmented polyurethane elastomer (PUR) was investigated. In order to investigate the interactions at the filler–matrix interface, nonmodified and commercially modified fillers (with methacrylsilane and octylsilane) were used. The PUR com-posites with 1.0, 2.0, 4.0, 6.0, and 9.0 vol % of all fillers were prepared by solution casting method. Surface free energy of the fillers and polymer matrix was determined using contact angle measurements with different testing liquids. Change in morphology was analyzed using optical polarization microscopy and distribution of the filler in polymer matrix using scanning electron microscopy. The influences of silica fillers on mechanical and thermal prop-erties of PUR were investigated. Results showed that sur-face treatment of silica filler with methacrylsilane and octylsilane reduces the agglomeration of particles that improves dispersion at microlevel. Addition of all fillers disrupts spherulite morphology and decreases crystallinity of the PUR matrix. Nonmodified silica nanofiller has the least pronounced influence on spherulite morphology and the lowest influence on polyurethane crystallinity and thus the best mechanical properties. Surface modification of silica with octylsilane has less influence on polyurethane crystallinity and on decreasing of mechanical properties than modification with methacrylsilane. V C 2011 Wiley Peri-odicals, Inc. J Appl Polym Sci 125: E181–E190, 2012
The influence of the addition of silica (Aerosil-200) (5-25 wt%) to polyurethane adhesives on their adhesion properties with non-chlorinated and surface-chlorinated rubbers has been studied. The chlorinating agent was Trichloroisocyanuric acid (TIC) in 2-butanone solution at a concentration of between 1 and 9 wt%. In general, silica produced an increase in the adhesive viscosity and an improvement of green (immediate) peel strength (especially with chlorinated rubber). The best results were obtained for a silica content of 10-20 wt%. However, the addition of silica did not improve the peel strength after a thermal ageing process. Polyurethane adhesives containing silica undergo an improvement in their resistance to degradation by chlorine on the rubber surface. On the other hand, the chlorination of silica produces the rupture of Si-O bonds and the formation of Si-H and Si-Cl groups. Furthermore, the stirring speed (directly related to the dispersion) of silica into the adhesive is an important parameter which affects the viscosity and peel strength. A stirring speed of 1000 rpm gives the best silica dispersion.
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).
Fundamental characteristics, general physical and mechanical behavior, and the recent developments in the knowledge of hot-melt adhesives (HMAs) are introduced. The current research and development status for HMAs is reviewed, with an emphasis on the development of new types/generations of HMAs. In particular, some crucial issues and challenges on the technological improvements and the materials development are discussed. On the basis of the current predicted shortage of energy resources and environmental concerns, prospective research on the development of green HMAs is suggested.
Recently developed strategies for isolating single-layer carbon sheets from graphite have enabled production of electrically conductive, mechanically robust polymer nanocomposites with enhanced gas barrier performance at extremely low loading. In this article, we present processing, morphology, and properties of thermoplastic polyurethane (TPU) reinforced with exfoliated graphite. For the first time, we compare carbon sheets exfoliated from graphite oxide (GO) via two different processes: chemical modification (isocyanate treated GO, iGO) and thermal exfoliation (thermally reduced GO, TRG), and three different methods of dispersion: solvent blending, in situ polymerization, and melt compounding. Incorporation of as low as 0.5 wt % of TRG produced electrically conductive TPU. Up to a 10-fold increase in tensile stiffness and 90% decrease in nitrogen permeation of TPU were observed with only 3 wt % iGO, implying a high aspect ratio of exfoliated platelets. Real- and reciprocal-space morphological characterization indicated that solvent-based blending techniques more effectively distribute thin exfoliated sheets in the polymer matrix than melt processing. This observation is in good qualitative agreement with the dispersion level inferred from solid property enhancements. Although also processed in solvents, property increase via in situ polymerization was not as pronounced because of reduced hydrogen bonding in the TPU produced.
Thermoplastic polyurethane elastomers (TPUs) are prepared including different amounts of rosin in their composition. Rosin is used either as an additive, mixed in the TPU solutions, or as a reactant in the chain-extension step of polymer synthesis. The properties of the materials are studied using solution viscosity measurements, size-exclusion chromatography, stress-controlled rheometry, differential scanning calorimetry, wide-angle X-ray diffraction, and contact angle determinations. Rosin as an additive does not markedly change the polymer properties. On the contrary, the use of rosin in the chain-extension step leads to sharp increases of viscosity and molar mass as well as improvements of rheological properties and changes in morphology: the crystalline regions are more affected (variations in the softening temperature and enthalpy) than the amorphous ones (quite constant glass-transition temperature). The conclusion is that rosin acts as an actual chain extender and that it modifies the organization of both the hard and the soft segments of the polymers. Furthermore, the TPUs are used as raw materials of solvent-based adhesives, which adhesion properties are characterized by T-peel tests of PVC/TPU adhesive joints. Rosin as an additive cannot improve the low tack (initial adhesive strength) of TPU, although as a chain extender or cochain extender (together with butane diol) rosin allows development of significant initial adhesive strengths, while keeping a high level of actual (maximal) adhesive strength. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3402–3408, 2001
Natural ultramicronized calcium carbonate and mixtures of fumed silica-natural ultramicronized calcium carbonate are proposed as fillers of solvent based polyurethane (PU) adhesives. PU adhesive containing only calcium carbonate shows similar rheological, thermal, mechanical, surface and adhesion properties than the PU adhesive without filler. Addition of 90 wt% fumed silica +10 wt% calcium carbonate mixture to PU adhesive produced a similar performance than the PU adhesive containing only famed silica. The increase in the amount of natural calcium carbonate in respect to fumed silica in the filler mixture produced detrimental effect on the rheological and mechanical properties of the PU adhesives (in respect to those provided by the PU adhesive only containing fumed silica), although the surface and adhesion properties were not noticeably modified.
Novel nanocomposites prepared by melt mixing of MWCNTs in a hot-melt adhesive PCL-based polyurethane are investigated. The nucleating effect of MWCNTs and the confinement they cause to polymer chains are considered. The broadening of the glass transition is indicative of a growth of the immobilized amorphous fraction adhered to MWCNTs. In the molten state the formation of a combined polymer/MWCNT network is observed. Practical requisites of hot melt adhesives, such as adequate melting temperature, crystallization degree, and viscosity are preserved when MWCNTs are added. Improvement of strength at roomtemperature and welding rate during cooling, are observed.
An elastomeric polyurethane/clay (PU/clay) nanocomposite based on poly(propylene glycol) (PPG), glycerol propoxylate, and toluene-diisocyanate (TDI) was synthesized by intercalative polymerization technology. The results of wide angle X-ray diffraction (WAXD) studies showed that the gallery distance of the clay in the hybrid was enlarged from 1.9 to 4.5nm or more. Introducing clay in the PU matrix resulted in an increase in both the tensile strength and elongation at beak. When the clay content reached about 8%, the tensile strength and elongation at break were two times and five times respectively to that of the pure PU. In addition, the clay intercalative route to the nanocomposite synthesis also effected the thermal properties of the nanocomposites. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1444–1448, 2001
Targeting specific aerospace coating applications, highly conductive carbon nanotubes were rigorously dispersed into a commercial topcoat PU matrix to produce nanocomposites for electrostatic dissipation and/or de‐icing coatings. Systematic evaluation on a range of properties that are pertaining to the targeted applications showed that, comparing with pure PU film, an addition of 1 wt.‐% functionalized MWNTs resulted in a significant improvement in the tensile strength and modulus; a 6.5 °C shift in glass transition temperature; a six orders of magnitude decrease in electrical resistivity and 24% improvement in thermal diffusivity. The durable, light color, and flexible nanocomposite with sufficiently low surface resistivity meet the requirements for aerospace coating applications.
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Polyester-based polyurethanes with embedded nanosilica particles were prepared. The viscosity of polyester resins without and with nanosilica was determined by rheoviscometry. The morphology and mechanical and optical properties of the polyurethane coatings were studied intensively with a transmission electron microscope, a pendulum hardness tester, a scanning probe microscope, an Instron testing machine, an abrader and an ultraviolet–visible spectrophotometer. The viscosity of the polyester resins increased as the nanosilica content increased. Nanosilica could basically be dispersed into the polyester and its polyurethane on a nanoscale. The addition of a small amount of nanosilica increased the hardness, abrasion resistance, and tensile properties of the polymer films. However, these mechanical properties could be worsened at higher nanosilica contents. The ultraviolet–visible spectra showed that the absorbance and reflection of ultraviolet–visible light by the polyurethane films increased as the nano-SiO2 content increased, especially at wavelengths of 290–400 nm. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 189–193, 2003
Polymer nanocomposites are polymer matrix composites in which the fillers are less than 100 nm in at least one dimension.
These composites have exhibited extraordinarily interesting properties. A defining feature of polymer nanocomposites is that
the small size of the fillers leads to a dramatic increase in interfacial area as compared to traditional composites. This
interfacial area creates a significant volume fraction of interfacial polymer with properties different from the bulk polymer
even at low loadings. The properties and structure of this interfacial region are not yet known quantitatively, presenting
a challenge both for controlling and predicting the properties of polymer nanocomposites. This paper provides a brief overview
of polymer nanocomposites with emphasis on the impact of the interfacial region.
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