Waterborne polyurethane dispersions obtained with polycarbonate of hexanediol intended for use as coatings

Three waterborne polyurethane dispersions derived from polycarbonate of hexanediol (PCD) with molecular weight of 1000 Da were synthesized by the acetone method and used as coatings for stainless steel plates. Different hard segments content in the polyurethanes were obtained by varying the isocyanate/macroglycol (NCO/OH) molar ratio. A decrease in the NCO/OH ratio produced an increase in the mean particle size as well as a decrease in the Brookfield viscosity of the dispersions. Furthermore, the greater the NCO/OH ratio the higher the urea and urethane hard segment content, the higher the glass transition temperature value and the higher the elastic modulus of the polyurethane was. On the other hand, the NCO/OH ratio affected the adhesion of the polyurethanes. The adhesion was evaluated by using three different procedures: T-peel strength tests of flexible PVC/waterborne polyurethane dispersion/flexible PVC joints; single lap-shear tests of aluminium/waterborne polyurethane dispersion/aluminium joints and cross-cutter adhesion test of polyurethane coatings on stainless steel pieces. Finally, several properties of the polyurethane coatings on stainless steel pieces were tested including Persoz hardness, gloss, chemical resistance and yellowness index.     

Preparation and characterization of waterborne polyurethane/silica hybrid dispersions from castor oil polyols obtained by glycolysis poly(ethylene terephthalate) waste

Castor oil polyols (COLs) have been synthesized from glycolyzed oligoester polyol in order to produce waterborne polyurethane (WPU)/silica hybrid dispersions. Soft drinks poly(ethylene terephthalate) (PET) bottles were depolymerized by glycolysis with different molar ratio of poly(ethylene glycol) ( PEG 400), in the presence of zinc acetate as catalyst. The obtained glycolyzed products were reacted with castor oil (CO) to attain castor oil polyols by the process of transesterification. Five castor oil polyols were used with hydroxyl values of 255, 275, 326, 366 and 426 mg KOH g⁻¹. Several castor oil-based, polyurethane/silica hybrid dispersions having soft segment content of 39.6% to 28.2% and two concentrations of SiO₂ nanoparticles (0.5 and 1.0) have been prepared.The incorporation effect of SiO₂ nanoparticles into the PU matrix and the hydroxyl functionality of the COLs on the thermal and mechanical properties of resulting polyurethane films has been examined by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal gravimetric analysis (TG) and measurement of the mechanical properties. The degree of phase separation (DPS) between oxide nanoparticles and hard segment, and particle size in the polyurethane, depends to some extent on nanosilica content and the hydroxyl functionality of the polyols employed in the polyurethane preparation process.Thermal stability of obtained hybrid materials depends on the hydroxyl functionality of the COLs and nanosilica content. The T_10% and T_50% (the temperature where 10 and 50% weight loss occurred) of WPU films decreased with the rise of OH functionality of castor oil polyols, caused by the increase of hard segment content. Glass transition temperature increased with increasing OH functionality and SiO₂ content. The hardness, adhesion and gloss quality of the polyurethane films were also determined with a view to assessing the effect of mole ratios of PET to glycol in glycolyzed products, the hydroxyl functionality and the SiO₂ content.     

Effect of annealing on the properties of waterborne polyurethane adhesive containing urethane-based thickener

Different amounts of hydrophobically modified ethoxylated urethane-based thickener (HEUR) were added to improve the rheology of waterborne polyurethane adhesives. The thickened solid adhesive films were thermally annealed and characterised by IR spectroscopy, plate–plate rheology, dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Hydrogen bonds played a key role in the thickening mechanism of polyurethane dispersions containing urethane-based thickener, along with ionic adsorption and micelles formation between hydrophobic groups. The adhesion properties were measured from T-peel test of leather/polyurethane adhesive/vulcanised styrene-butadiene rubber joints. Optimal results were obtained when water in the waterborne polyurethane adhesive (just before joint formation) was removed under open air, while forced air drying impeded the complete removal of water. On the other hand, the thermal annealing did not greatly affect the rheological and thermal properties of the thickened polyurethanes.     

Coatings prepared from waterborne polyurethane dispersions obtained with polycarbonates of 1,6-hexanediol of different molecular weights

Waterborne polyurethane dispersions (PUDs) were synthesized with polycarbonates of 1,6-hexanediol of different molecular weight (500–3000 Da) and their properties, adhesion (Hatch adhesion) and coatings on stainless steel properties (Pencil hardness, Persoz hardness, gloss at 60°, chemical resistance, yellowness index) were characterized. The hatch adhesion of the polyurethane coatings to stainless steel was very good and decreased slightly by increasing the molecular weight of the polycarbonate of 1,6-hexanediol. Both the Pencil and Persoz hardness values of the coatings increased by increasing the hard segments content in the polyurethane, i.e. by decreasing the molecular weight of the polycarbonate of 1,6-hexanediol, whereas the gloss and the yellowness index were lower for the coatings obtained with the polycarbonate of 1,6-hexanediol of molecular weight of 500 Da. Very good chemical resistance against ethanol for all polyurethane coatings on stainless steel plates was obtained but for long time of ethanol in contact with the coating surface the chemical resistance decreased, more markedly for the polyurethane coating obtained with the polycarbonate of 1,6-hexanediol of higher molecular weight. In summary, the segmented structure of the waterborne polyurethane dispersion determined the properties of the polyurethane coatings obtained from them.     

Effect of 3-Aminopropyltriethoxysilane on polycarbonate based waterborne polyurethane transparent coatings

A series of waterborne polyurethane (WPU) dispersions modified with different contents of 3-aminopropyltriethoxysilane (APTES) were synthesized based on poly(1,6-hexyl 1,2-ethylcarbonate) diol (PHEC) and isophorone diisocyanate (IPDI), and the films were obtained by casting the dispersions on Teflon molds. Effects of APTES content on the particle size and viscosity of the dispersions were studied. The structure and properties of the resulting films were investigated by Fourier transform infrared spectroscopy, wide angle X-ray diffraction measurement, dynamic mechanical analysis, thermogravimetric analysis and mechanical testing. The experimental results showed that the incorporation of APTES played an important role in the enhancement of the water and toluene resistance and mechanical properties of the SPU films. Young's moduli and ultimate tensile strengths were improved from 8.0 to 451 MPa and 6.5–19 MPa respectively as the APTES content increased from 1 wt.% to 20 wt.%. The ability of scratch resistance was enhanced, when the content of APTES increased to 20 wt.%, the 3H pencil could not mar the surface. Moreover, the transmittance spectra indicated that the coatings showed high transparence.     

聚碳酸酯型水性聚氨酯的制备与性能研究

通过采用聚碳酸酯二醇CD2000、二羟甲基丙酸(DMPA)和异佛尔酮二异氰酸酯(IPDI)为原料,制备出了透明的水性聚氨酯(WPU)。通过红外光谱仪、动态激光光散射仪和粘度计分别研究了聚氨酯的微相分离、DMPA含量对WPU粒径及粘度的影响,并进一步研究了NCO/OH比值和扩链系数对材料性能的影响。结果表明,随着DM-PA含量的增加WPU的粒径逐渐减小,而粘度呈现先减小后增加的趋势;随着NCO/OH比值的增加,薄膜微相分离程度愈大,断裂伸长率和弹性回复率逐渐降低,而拉伸强度先增加后减小;随着扩链系数的增加,拉伸强度和断裂伸长率呈现先增加后减小的趋势。     

不同固含量对水性聚氨酯性能的影响

以异佛尔酮二异氰酸酯(IPDI)、聚己二酸丁二醇酯(PBA)为主要原料合成了不同固含量的水性聚氨酯乳液(WPU)。红外光谱表征了WPU的结构,并探讨了WPU的固含量对乳液粒径和胶膜力学性能、热性能及其微观结构的影响。结果表明,随着固含量的增加,胶膜拉伸强度降低,断裂伸长率升高;且固含量低的WPU乳液粒径分布集中,胶膜平整,固含量高的则反之;此外,不同固含量的WPU的热性能也有一定的差别,随着固含量的增加,胶膜的最大分解速率有所降低。     

不同固含量对水性聚氨酯性能的影响

以异佛尔酮二异氰酸酯(IPDI)、聚己二酸丁二醇酯(PBA)为主要原料合成了不同固含量的水性聚氨酯乳液(WPU)。红外光谱表征了WPU的结构,并探讨了WPU的固含量对乳液粒径和胶膜力学性能、热性能及其微观结构的影响。结果表明,随着固含量的增加,胶膜拉伸强度降低,断裂伸长率升高;且固含量低的WPU乳液粒径分布集中,胶膜平整,固含量高的则反之;此外,不同固含量的WPU的热性能也有一定的差别,随着固含量的增加,胶膜的最大分解速率有所降低。     

Influence of the chemical structure of PUR prepolymers on thermal stability

The thermal stability of adhesives for load-bearing construction has been one of their key parameters since engineered wood products were introduced in timber construction. In the case of one-component moisture-curing polyurethane (1C PUR) adhesives, knowledge about relationships between their chemical structure and the resulting bonding properties is limited, especially under high-temperature conditions. In this study the structure-property relationships of 1C PUR prepolymers were analyzed in the temperature range from 20 to 200 °C by means of mechanical and rheological tests. NCO-terminated urethane prepolymers were prepared from systematically varied MDI and polyether mixtures. The structural parameters investigated were the urea and urethane group content, cross-link density, ethylene oxide content and the adjustment of functionality via NCO or polyether component. Bonded wood joints were tested for their tensile shear strength and polymer films were analyzed by means of DMA and DSC. The results revealed a significant influence of hard segment content and cross-link density on the thermal stability of the prepolymers. Not all parameters that affect the film properties significantly influence bonding.     

Thermal decomposition of polyurethane pressure-sensitive adhesives dispersions

The thermal degradation of polyurethane pressure-sensitive adhesives (PSAs) at temperature 600 °C was investigated by the application of pyrolysis-gas chromatography technique. The present study was undertaken in order to determine the key thermal degradation products of polyurethane PSA based on isophorone diisocyanate (IPDI), polypropylene glycol (PPG), hydroxylated polybutadiene (HTPB), dimethylolpropionic acid (DMPA) and to elucidate the mechanism of the polyurethane PSAs pyrolysis.     

Characterization of waterborne polyurethane adhesives containing different amounts of ionic groups

Waterborne polyurethane adhesives are an interesting alternative to the current solvent-based polyurethane adhesives used in footwear industry. In this study, different aqueous polyurethane dispersions were prepared by using the prepolymer mixing process. The ionic groups content in the polyurethane ionomer structure was varied by changing the amount (5 and 8 wt% (with respect to the prepolymer weight) of the internal emulsifier—dimethylolpropionic acid (DMPA). The decrease in the DMPA content slightly increased the particle size in number due to the decrease in both the hydrophilicity of the polyurethane ionomer, and the electrolytic stability of the aqueous polyurethane dispersion. Furthermore, the lower the DMPA amount, the lower the hard segment content in the ionomer and the higher the crystallinity of the polyurethane; however, the resistance to flow under temperature (i.e. thermoplasticity) was reduced. The resistance to thermal degradation of the polyurethane ionomer increased by decreasing the DMPA content due to the lower hard segment content. Finally, high initial adhesive strength was obtained and the adhesion to PVC increased as the DMPA content in the polyurethane ionomer decreased.     

Water resistance of the membranes for UV curable waterborne polyurethane dispersions

The water absorption of the membranes made from UV curable waterborne polyurethane dispersions (UV-PUDs) was investigated systematically and correlated with the nature of the polymer and its gel content after curing. It was found that the water absorption of the membranes was reduced significantly by using polyester polyols, reducing the COOH content and increasing the gel content through a higher CC level. In particular, the membranes made from polyurethanes having hydroxyl-terminated polybutadiene (HTPB) or modified with dihydroxybutyl-terminated polydimethylsiloxane (PDMS) presented a superior water resistance. The results showed a linear relationship between the water absorption and the surface tension of the membrane.     

Studying the effects of chain extenders chemical structures on the adhesion and mechanical properties of a polyurethane adhesive

Chain extenders including diethanol amine (DEA) and 2-cyano-N,N-bis-hydroxyethyl acetamide (CNBA) were utilized to enhance the adhesion and mechanical properties of a polyurethane (PU) adhesive. The adhesion and mechanical properties of the adhesives were studied by peel test, tensile test and dynamic thermal analysis (DMTA) respectively. Results revealed that both chain extenders (DEA and CNBA) increased peel test modulus. The cross-linking density and toughness of the adhesive were significantly increased using chain extenders. Results showed that chain extender without side chain (DEA) could improve the adhesion and mechanical properties of the adhesive greater than chain extender with aliphatic side group (CNBA).     

The influence of nanosilver on thermal and antibacterial properties of a 2 K waterborne polyurethane coating

A two-component (2 K) waterborne polyurethane coating containing nanosilver (200 ppm) was prepared and compared to the blank coating with no nanosilver. The coatings were inoculated with Escherichia coli and Staphylococcus aureus by the agar-well diffusion method. According to the results, silver nanocomposite coating exhibited a growth reduction on both types of bacteria. The cross-section of samples was examined by scanning electron microscopy (SEM). The micrographs depicted uniform dispersion of Ag nanoparticles in the polyurethane matrix. Fourier transform infra-red (FTIR) spectra of the coatings revealed intensification of carbonyl group stretching band in the presence of nanosilver, which could be related to the partial protection of isocyanate groups from decomposition in the presence of water. Enhancement of thermal properties was observed by differential scanning calorimetry and thermogravimetry.     

Design and properties of UV cured polyurethane dispersions

UV curable polyurethane dispersions (UV-PUDs) having different prepolymer chain length, different types of capping agent (2,3-epoxy-1-propanol (glycidol) and 2-hydroxyethylacrylate (HEA)) and ionic center have been synthesized. Films based on polyurethane prepolymer were tack free prior to cure and showed high elongation at break over 200% as well as high hardness and modulus, especially when the terminal isocyanate groups were capped with glycidol.     

Role of the interactions between carbonate groups on the phase separation and properties of waterborne polyurethane dispersions prepared with copolymers of polycarbonate diol

Different aliphatic waterborne polyurethane dispersions (PUDs) were synthesized by using different polyols (M_w: 1000 Da) of randomly copolymerized polycarbonate diols with hexamethylene and pentamethylene (C6–C5), tetramethylene (C6–C4) and trimethylene (C6–C3); these copolymers differed in the length of the methylene groups and the structural regularity due to the combination of even and odd units. Brookfield viscosity, extent of particle crowding and broadening of the particle size distribution of the PUD synthesized with C6–C4 polyol followed a different trend than for the other because of the even number of methylene units in the polyol. The PUDs showed monomodal particle size distribution which was narrower in C6–C4 (i.e. the dispersion with higher structural regularity) and the mean particle size decreased by decreasing the length of the methylene unit of the copolymer.The properties of the polyurethanes were affected by the phase separation between the hard and soft segments, the more regular packing of even methylene units in the copolymer and the crystallized polar segments due to carbonate groups. Thus, the glass transition values of the soft segments in the polyurethanes were similar because of the more regular packing of even methylene units in C6–C4 polyol and the crystallized segments produced by interactions of carbonate groups. PU(C6–C5) and PU(C6–C4) showed similar degree of phase separation, the higher degree of phase separation corresponded to PU(C6–C3). Furthermore, the crystallinity of the polyurethanes increased with decreasing the number of methylene units in the polyol, but PU(C6–C4) was the most crystalline because of the more regularly packed even methylene groups in the polyol chain. The thermal stability of the polyurethanes increased from PU(C6–C5) to PU(C6–C3) because the more net interactions between the carbonate groups in the soft segments. The lower was the number of methylene groups between carbonate units in the copolymer, the higher was the elastic modulus of the polyurethanes. The tensile strength and elongation-at-break values of the polyurethanes increased by increasing the number of methylene groups between carbonate units in the copolymer. Finally, the peel strength was maximal in the joint made with PU(C6–C5) and the shear strength was the highest in the joint made with PU(C6–C3), in agreement with the variation of the viscoelastic and mechanical properties of the polyurethanes.     

Preparation and properties of starch thermoplastics modified with waterborne polyurethane from renewable resources

A waterborne polyurethane (PU) aqueous dispersion was synthesized from castor oil, and blended with thermoplastic starch (TPS) to obtain a novel biodegradable plastic with improved physical properties. The effect of PU content on the morphology, miscibility and physical properties of the resulting blends was well investigated by scanning electron microscopy, differential scanning calorimetry, dynamic mechanical thermal analysis and measurements of mechanical properties and water sensitivity. The research results show that the blends exhibit a higher miscibility when PU content is lower than 15 wt% due to the hydrogen bonding interaction between urethane groups and hydroxyl groups on starch, whereas obviously phase separation occurs in the blends with more than 15 wt% PU. Incorporating PU of 4-20 wt% in TPS results in the blends with improved Young's modulus (40-75 MPa), tensile strength (3.4-5.1 MPa), elongation at break (116-176%). Further, PU also plays an important role in improving the surface- and bulk-hydrophobicity and water resistance of the resulting blends.     

Incidence of the polyol nature in waterborne polyurethane dispersions on their performance as coatings on stainless steel

Three waterborne polyurethane dispersions derived from polyester, polyether and polycarbonate diols with molecular weight of 1000 Da were synthesized by the acetone method and used as coatings on stainless steel 304 plates. The properties of the dispersions and the polyurethane films were influenced by the polyol nature. The polyurethanes obtained with polyether or polyester showed higher degree of phase separation between the soft and the hard segment. The higher adhesive strength under shear stresses was obtained in the joints produced with the waterborne dispersion obtained with polycarbonate diol. The properties of the polyurethane coating obtained with polycarbonate diol on stainless steel 304 were significantly higher as compared with the others. Improved performance of coatings obtained with polycarbonate diol was ascribed to the higher polarity of the carbonate groups that contributed to additional hydrogen bond formation between soft segments with respect to those obtained with polyether or polyester     

高固含量阳离子水性聚氨酯的性能研究

以聚酯二元醇为软段、异佛尔酮二异氰酸酯(IPDI)和N-甲基二乙醇胺(N-MDEA)为主要原料,采用丙酮法合成了高固含量(约50%)的CWPU(阳离子水性聚氨酯),并着重探讨了N-MDEA含量、软段种类对该CWPU的基本性能、结晶性能、力学性能和粘接性能等影响。结果表明:当w(N-MDEA)=5.5%～7.0%(相对于预聚体质量而言)时,可制得稳定的高固含量CWPU;软段的结晶性越好,高固含量CWPU的力学性能和粘接性能越高;当软段为聚己二酸己二醇酯(PHA)时,相应高固含量CWPU的邵A硬度(84)、拉伸强度(55 MPa)和剥离强度(初始剥离强度、24 h剥离强度为68.2、90.4 N/25 mm)相对最大,可作为胶粘剂使用。