Reactive hot melt polyurethane adhesives modified with pentaerythritol diacrylate: synthesis and properties

Pentaerythritol diacrylate (PEDA) was synthesized by direct esterification from acrylic acid and pentaerythritol, and the reactive hot melt polyurethane adhesives (PURs) with high green strength were prepared from Poly(1,6-hexamethyleneadipate), PHA-3000, two kinds of Poly(propylene glycol) (PPG-1000 and PPG-4000) and PEDA as well as terpene-phenolic resin. Five samples of PURs with different weight percent (α) of PEDA (α = 0, 3, 5, 7, and 10 wt%), were obtained. The rheological properties, thermal stability, and mechanical properties of the samples were investigated. The results showed that the melt viscosity (η) and the storage shear modulus of the samples increase with the increase in α, while the thermal stability changes little. The bonding strength of the samples after 10 min, 30 min, and 48 h was assessed by 180° peel tests of Fabric 6535/adhesives/Fabric 6535 stacks. The results showed that the green strength after 30 min increases with the increase in α when α is not higher than 7 wt%.     

Recycling of rigid polyurethane foam: Micro-milled powder used as active filler in polyurethane adhesives

Rigid polyurethane (PUR) foams are widely used as heat insulation material in construction industry or for electronic appliances manufacturing. After finishing their life-time, it is necessary to eliminate foam wastes. The aim of this study was to prepare a pair of industrial PUR adhesives of medium viscosity containing recycled rigid PUR foam. Three methods of milling were tested: knife-milling, two-roll milling, and ball-milling. Only two-roll milling gives the PUR micro-powder usable for following adhesives modification. The micro-powder was used as passive filler in PUR adhesives and potential reactivity for polyol pack replacement was studied. Hydroxyl and amine numbers were determined in mixture with virgin polyol. One-component PUR prepolymer adhesive was prepared using various dosages of the micro powder and the tensile strength of bound wood was measured. As additional parameters, also free film adhesive mechanical parameters were tested and particle size distribution of the micro powder was analyzed. Two adhesive formulations were prepared for independent evaluation of the micro powder reactivity. The results showed growing of the mechanical strength of wood bonding with growing dosage of the micro powder.     

Thermische und mechanische eigenschaften von polyurethanen mit mesogenen diolkomponenten

Nonsegmented and segmented polyurethanes (PURs) containing 4,4′-di(ω-hydroxyalkoxy)biphenyls were synthesized and the effect of the spacer length of the mesogenic diol on thermal and mechanical properties was investigated. DSC measurements showed similar thermal transitions for the segmented and the nonsegmented PURs. However, for the segmented PURs a shift to lower temperatures was observed. Polarization microscopy indicated the existence of LC phases in the nonsegmented PURs. The moduli of films of segmented PURs increased with growing length of the spacer, particularly at temperatures ≤40°C, due to decoupling of motions of the mesogenic and the urethane part. Decoupling also promotes formation of larger domains of the mesogenic groups. Flow was observed above a temperature dependent critical stress value. Chemical cross-linking below the thermal transitions improved the mechanical film properties as the physical network, due to domains of the mesogenic groups, superposes the chemical network. This was demonstrated with a PUR containing COOH groups crosslinked with a melamine resin at temperatures below or above the thermal transitions.     

The effect of flow on the physical properties of polyurethane/carbon nanotubes nanocomposites: Repercussions on their use as electrically conductive Hot‐Melt adhesives

The properties of multiwall carbon nanotubes (MWCNT)/polyurethane (PUR) nanocomposites after being submitted to flow, i.e., in conditions similar to their application as electrically conductive adhesives (ECA), are investigated. A decrease of the elastic modulus is observed after flow is stopped, compatible with a rearrangement of the MWCNT/PUR network during flow. The implications of the viscoelastic results on probe‐tack data are elucidated and a slightly higher energy of adhesion is observed for sheared samples. Dynamic viscoelastic measurements reveal that crystallization of PUR is fastened with MWCNTs, shortening the solidification process for samples submitted to flow or not. Electrical conductivity results show that the 4 wt% MWCNT/PUR nanocomposite can be submitted to flow and give, on cooling to room temperature, values of the electrical conductivity between 10⁻² and 10⁻¹ Siemens /m. 2 wt% MWCNT/PUR sample presents a shear induced semiconductor to insulator transition and a temperature‐induced isolator to semiconductor transition. We conclude that MWCNT/PUR nanocomposites are good candidates to develop Hot Melt ECAs, since they display satisfactory viscosity, tack, crystallization (linked to permanent adhesion), and electrical conductivity. POLYM. COMPOS., 36:704–712, 2015. © 2014 Society of Plastics Engineers     

Synthesis,characterization, and performance evaluation of novel stabilized TDI‐based polyurethane coatings under accelerated weathering

Some toluene diisocyanate (TDI)‐based polyurethane resins (PURs) for coating applications were synthesized with castor oil and their performance was estimated under accelerated UV weathering with and without a novel UV absorber. Changes in physical properties, chemical structure, and color of the samples were monitored by mechanical property testing, FTIR spectroscopy, and colorimetry, respectively. A stable polyurethane coating was achieved at 0.5% concentration of additive in the host matrix. Mechanical properties were also retained as in the pristine PUR after mixing. Commercial Tinuvin P and benzotriazole‐based novel UV absorbers were found to improve the photoresistance of the PUR coating, and the highest efficiency of the novel UV absorber against weathering was estimated at 0.5 wt% concentration. J. VINYL. ADDIT. TECHNOL. 11:13–20, 2005. © 2005 Society of Plastics Engineers.     

Wood/adhesive interactions and the phase morphology of moisture-cure polyurethane wood adhesives

Two moisture-cure polyurethane adhesives (PURs) were studied: a model (MPUR) prepared from a symmetrical diisocyanate that gave rise to a continuous soft phase, and a commercially relevant adhesive (CPUR) prepared from an asymmetrical polyisocyanate that resulted in a continuous hard phase. Atomic force microscopy revealed that the size and size distributions of the respective dispersed phases were altered by wood, as observed in localized specimen regions. Bulk effects were observed with dynamic mechanical analysis; both soft and hard phase MPUR relaxations were altered by wood (increased transition temperatures), whereas only the continuous CPUR hard phase revealed wood-induced changes. Furthermore, infrared analysis showed that wood promoted the formation of hydrogen-bonded urea structures in CPUR bondlines. Significant wood/PUR interactions were detected, however it was not possible to determine if the effects arose from direct intermolecular associations, or from indirect effects arising from the mere presence of wood and how this impacts forces acting upon the liquid adhesive (i.e. moisture transport, differing interfacial energies through which transport occurs, and CO₂ bubble nucleation). Regardless, it is clear that PUR studies should be conducted under conditions that simulate real wood/PUR bondlines.     

Pressure Sensitive Adhesives Based on Oleic Acid

Existing pressure sensitive adhesives (PSA) are mostly based on petrochemical‐based polymers. This study reveals a new class of bio‐based polymers that can be used as PSA. The polymers are hydroxyl‐containing polyesters from the step‐growth polymerization of epoxidized oleic acid (EOA), an AB‐type monomer containing both a carboxylic acid group (A) and an epoxy group (B). The monomer is derived from epoxidation of renewable methyl oleate followed by selective hydrolysis of the ester group. The polymers (PEOA) of EOA were characterized for their chemical structure and molecular weight. The PEOA after being cured with a very small amount of a crosslinking agent could serve as a PSA with high peel strength, high tack force, superior shear resistance, excellent aging resistance, and excellent thermal stability. The PSA contains 99 wt% of green renewable materials. The PSA were also characterized for their viscoelastic properties and thermal properties.     

The physical and mechanical properties of polyurethanes from oleic acid polyols

Three different polyester polyols, with various oleic acid content, were used in the preparation of polyurethane (PUR) coatings. The polyols were designated as Alk28, Alk40, and Alk65, in which 28, 40, and 65 represent the percentage of oleic acid of the polyol formulations. These polyester polyols were reacted with aromatic diisocyanate [toluene diisocyanate (TDI)] to form PUR coatings. The acid value, hydroxyl value, molecular weight, and viscosity of the polyols have been determined. The reaction between the polyols and TDI was studied by Fourier Transform Infrared spectroscopy and X‐ray diffraction (XRD). The effects of varying NCO/OH ratio and oleic acid content of polyols on physical and mechanical properties of PUR films were studied. XRD results indicate that the samples are amorphous. PURs, made with Alk28, have the best mechanical properties followed by Alk40 and Alk65. The mechanical properties of the samples have increased as the NCO/OH ratio was increased from 1.2 to 1.6. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The effect of the heat treatment of spruce wood on the curing of melamine–urea–formaldehyde and polyurethane adhesives

The effect of the heat treatment of spruce wood on the curing of melamine–urea–formaldehyde (MUF) and polyurethane (PUR) adhesives was monitored by measuring their rheological properties by means of a rheometer. Instead of the standard aluminium discs, wooden discs, made from heat-treated wood with different degrees of thermal modification and conditioned in different climates, were used. The wooden discs provided more realistic curing of the adhesives compared to the real-life bonding of wood, because of solvent absorption. The results of the rheological measurements suggested that the modified wood inhibited the curing of MUF and PUR adhesives. The curing of the MUF adhesive was slower because of the reduced absorption of water from the adhesive. The curing of the one-component PUR adhesive was affected by the lower moisture content (MC) of the modified wood.     

Effects of various polyurethanes on the mechanical and structural properties of an epoxy resin

Polyurethanes (PURs) obtained from poly(ethylene glycol)s (PEGs) and polyoxypropylene diols (POPDs) of different molecular weights were used as modifiers of diglycidyl ether of bisphenol A. The impact strength, critical stress intensity factor, stress, and strain during three‐point bending were measured as functions of the PUR type and content. Scanning electron microscopy and infrared spectroscopy were employed for the structure and morphology analysis. The addition of 10 or 15% PUR to the epoxy resin resulted in the most enhanced mechanical properties. However, a modifier loading higher than 15% led to decreases in the impact strength, critical stress intensity factor, and flexural strength. Moreover, shorter flexible segments in PUR obtained from lower molecular weight PEG led to stronger composites, whereas composites containing PUR based on lower molecular weight POPD with long flexible segments exhibited higher toughness and strain at break and lower impact strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermal stability of structural one‐component polyurethane adhesives for wood—structure‐property relationship

The relationship between the chemical structure of commercial polyurethanes and temperature‐dependent creep properties was determined in full scale tests and the results were compared with thermomechanical analysis. Comparison of mechanical performance with ¹³C‐NMR spectroscopy studies elucidated important structure‐property relationships, which either allow the reduction or elimination of temperature‐dependent creep in one‐component polyurethanes (1C‐PUR) adhesives for wood. The combination of the relative content of still reactive, free ? NCO groups on the polyurethane, careful selection of the degree of resin polymerization and a slower rate of reaction are the three most significant parameters that have to be controlled to overcome the problem of temperature‐dependent creep found in 1C‐PUR adhesives. The results obtained indicate that adhesives presenting a combination of a higher content of still unreacted ? NCO groups, a lower degree of polymerization and slower reaction rate are capable to counteract problems of high sensitivity of polyurethane to temperature‐dependent creep. Two commercial polyurethanes that fulfil the latter requirements and exhibit almost no creep were identified and characterized. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5698–5707, 2006     

Properties of phenol‐formaldehyde resins prepared from phenol‐liquefied lignin

In this study, alkaline lignin (AL), dealkaline lignin (DAL), and lignin sulfonate (SL) were liquefied in phenol with sulfuric acid (H₂SO₄) or hydrochloric acid (HCl) as the catalyst. The phenol‐liquefied lignins were used as raw materials to prepare resol‐type phenol‐formaldehyde resins (PF) by reacting with formalin under alkaline conditions. The results show that phenol‐liquefied lignin‐based PF resins had shorter gel time at 135°C and had lower exothermic peak temperature during DSC heat‐scanning than that of normal PF resin. The thermo‐degradation of cured phenol‐liquefied lignin‐based PF resins was divided into four temperature regions, similar to the normal PF resin. When phenol‐liquefied lignin‐based PF resins were used for manufacturing plywood, most of them had the dry, warm water soaked, and repetitive boiling water soaked bonding strength fitting in the request of CNS 1349 standard for Type 1 plywood. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

单组分聚氨酯反应型热熔胶的研制

以异氰酸酯和多元醇为主要原料合成了系列单组分反应型湿固化聚氨酯热熔胶(PUR),考察了不同的软段结构、-NCO含量、固化时间、催化剂和增粘树脂等对其性能的影响。研究结果表明,采用自制的多元醇,设定w(-NCO)≈3.5%,当w(催化剂)=0.1%、w(增粘树脂)=20%时,所得PUR的综合性能较好,开放时间为7min,固化时间为24h,拉伸强度达到9.3MPa,初粘强度达到0.44MPa,剪切强度达到7.9MPa。     

Thermal degradation of biomedical polyurethanes—A kinetic study using high‐resolution thermogravimetry

The kinetics of thermal degradation of polyurethanes (PUR) has been studied by means of high‐resolution and constant heating rate thermogravimetry (TG), under nitrogen and synthetic air atmospheres. The high‐resolution TG provided a way to increase resolution with decreasing the time of data acquisition. In this mode, the heating rate is dynamically varied to maximize resolution. A method to calculate the kinetic parameters from this technique was used. The TG curves showed two or three decomposition steps, depending on the atmosphere employed. The parameters calculated for the PUR decomposition were the activation energy, reaction order, and preexponential factor. A method to estimate the polymer lifetime was also used. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 910–919, 2001     

高压CO_2流体发泡制备微孔PVC/PUR–T泡沫材料

以聚氯乙烯(PVC)、热塑性聚氨酯弹性体(PUR–T)为原料,通过溶液共混方法,用四氢呋喃(THF)溶解混合物,浇涛在聚四氟乙烯模具中制得PVC/PUR–T共混材料,采用高压CO_2为发泡剂用间歇发泡法制备PVC/PUR–T发泡共混材料。通过对解吸附时间的测定,确定了饱和时间为24 h。通过改变饱和压力得到一系列不同体积膨胀倍率和泡孔大小的材料,随着PUR–T含量的增加,体积膨胀倍率呈下降的趋势;PUR–T含量为5%时,混合材料的泡孔密度最大,随后又会降低,同时随着饱和压力的提高,试样的泡孔密度随之变大。在对发泡样品进行力学性能测试时,发现加入5%的PUR–T对断裂伸长率影响不大,但随着PUR–T含量的增加,断裂伸长率增加;随着PUR–T含量的增加,发泡共混物的拉伸强度也增加,说明PUR–T的加入增强了体系的强度和韧性。     

Preparation and performance of lignin–phenol–formaldehyde adhesives

Steam explosion lignin phenol formaldehyde (SEL–PF) adhesives were prepared by ternary gradual copolymerization. The parameters for the phenolate of steam explosion lignin (SEL) and preparation of SEL–PF adhesives were optimized. Under the optimum phenolate conditions, the phenolic hydroxyl content of lignin increased by 130%, whilst the methoxyl content was reduced by 68%. The SEL–PF adhesives were used to prepare plywoods by hot-pressing. The pH value, viscosity, solid content, free phenol content and free formaldehyde content of SEL–PF adhesives were investigated. The bonding strengths of the plywoods glued with SEL–PF adhesives were determined. The maximum SEL replacement percentage of phenol reached 70 wt%, and the properties of adhesives and plywoods met the Chinese National Standard (GB/T 14732-2006) for first grade plywood.     

High‐build alkyd urethane coating materials with a partially solvolyzed waste polyurethane foam

Solvent‐borne alkyd urethane coating compositions containing 20 or 40 wt% (on solids) of partially solvolyzed waste polyurethane foam (PUR) were prepared and analyzed. Partial solvolysis of the soft polyurethane foam was carried out via extrusion with either 5 or 10 wt parts of solid polyol, that is, trimethylolpropane (TMP) or tris(hydroxymethyl)aminomethane. The addition of a partially solvolyzed PUR significantly affected the properties of cured coats, such as adhesion to a steel substrate, hardness, abrasion resistance, indentation depth, water absorption, tensile strength, and thermal stability. Moreover, the viscosity of ready‐to‐use coating compositions (containing a diisocyanate hardener) depended on a type and content of the processed PUR. Generally, a set of the most positively upgraded properties (viscosity, hardness, tensile strength, and thermal stability) was observed for coating compositions containing 20 wt% of PUR extruded with a higher dose of TMP (i.e., 10 wt parts of TMP/100 wt parts of waste polyurethane foam). POLYM. ENG. SCI., 55:2174–2183, 2015. © 2015 Society of Plastics Engineers     

基于两种双硫键自修复聚氨酯制备及性能

以异佛尔酮二异氰酸酯(IPDI)和双(2-羟基乙基)二硫醚(DTBO)为硬段,聚四氢呋喃(PTMG)为软段,β-巯基乙醇(ME)为封端剂,制备巯基封端且含双硫键的聚氨酯(PUR)预聚物,利用巯基易氧化的特点,用H2O2/NaI进行氧化,合成分子链内和分子链端均含有双硫键的自修复交联PUR.采用傅立叶变换红外光谱仪、差示...     

Thermal degradation studies on rigid polyurethane foams blown with pentane

The effect of sodium dihydrogenphosphate, trisodium pyrophosphate, and sodium aluminocarbonate on the thermal decomposition of rigid polyurethane (PUR) foams, based on diphenylmethane‐4,4‐diisocyanate, diphenyl‐2,2‐propane‐4,4‐dioxyoligo(ethylene oxide), and oxyalkylenated toluene‐2,6‐diamine, blown with pentane, was studied. Thermogravimetric (TG) data have shown that there is a stabilization effect of additives in the initial stage of degradation, both in nitrogen and air atmosphere, and the decomposition proceeded in two steps up to 600°C. Results of the kinetic analysis by the isoconversional methods of Ozawa–Flynn–Wall and Friedman yielded values of (apparent) activation energy (E_a) and preexponential factor (A). For phosphate‐stabilized PUR samples, E_a remained stable over a broad area of the degree of conversion, while for carbonate‐containing sample two regions of E_a were observed. Further advanced kinetic analysis by a nonlinear regression method revealed the form of kinetic function that was the best approximation for experimental data—for a two‐stage consecutive reaction the first step was the Avrami–Erofeev nucleation‐dependent model, and the second step was a chemical reaction (1st or nth order) model. The integrated thermogravimetric (TG)/Fourier transform infrared (FTIR) technique probed the thermal degradation of modified PURs by analyzing the evolved gases. The solid residue remaining at different temperatures was identified by diffuse reflection FTIR (Kubelka–Munk format). The complex thermal behavior was discussed on the basis of the obtained results—it can be shown that the global stabilization effect is a multistage process whose initial conditions are of critical importance in governing the nature of the entire process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2319–2330, 2003     

复合发泡体系对PUR–T发泡材料性能的影响

采用化学发泡法,用热塑性聚氨酯(PUR–T)及偶氮二甲酰胺(AC)/Na HCO3,AC/尿素及4,4’–氧代双苯磺酰肼(OBSH)/Na HCO3,OBSH/尿素复合发泡剂和交联剂甲苯二异氰酸酯(TDI)制备出交联型PUR–T发泡材料,通过万能电子试验机、发泡倍数和扫描电子显微镜分析比较了不同复合发泡剂的发泡效果,探讨了AC/Na HCO3用量配比和TDI用量对PUR–T发泡材料力学性能、发泡倍数和泡孔结构的影响。结果表明,AC/Na HCO3复合发泡剂对PUR–T的发泡效果最佳,泡孔均匀细密且结构最为稳定;当AC和Na HCO3用量均为0.2份、TDI用量为1.2份时,发泡剂的发泡速率和PUR–T的交联速率最匹配,发泡倍数为1.421倍,发泡效果最佳,制得的PUR–T发泡材料的力学性能最好,其拉伸强度达11.23 MPa,断裂伸长率达311%。