Curing Of Polyurethane Research Articles

Maintenance robot for remote assembly of protective jackets on live gas risers

Combining high-rise robotics research and polyurethane (PU) repair techniques presents new opportunities and unique challenges for utility pipe maintenance. Aiming at solving the complex pose alignment issue of robots and control PU curing, this paper automates the repair process by assembling protective jackets with PU foam. A wire-hoisted robot was equipped with anchors and a twin-gripper mechanism for workspace definition, along with a manipulator that positioned a pair of mirrored end effectors to perform surface polishing, jacket installation, and PU curing onto the pipe. Consequently, the robot pose was stabilized. The jacket pair was assembled onto the pipe with high precision, yielding high-quality repair, a success rate >96%, short cycle time, and low material wastage. This research may inspire innovative automation approaches for building maintenance, while utility companies can deploy the robot system for sustainable pipe service life.

Rheological, Structural, and Strength Characteristics of Cold-Cured Polyurethane Synthesized in the Presence of the Complex of Tributyl Phosphate with Zinc Dichloride

The possibility of using [(C4H9O)3P=O]2ZnCl2 as a catalyst for preparing cold-cured polyurethane from a mixture of hydroxyl-containing oligomers and polyisocyanate was examined. The kinetic characteristics of curing were studied by viscometry, and the physicomechanical characteristics of compounds synthesized in the presence of [(C4H9O)3P=O]2ZnCl2 were determined. The influence of the curing rate on the structure of hydrogen bonds in the polymer matrix and on the glass transition point of the polyurethane was analyzed using Raman spectroscopy and differential scanning calorimetry. The results obtained show that curing of polyurethane in the presence of [(C4H9O)3P=O]2ZnCl2 occurs at a high rate and leads to the formation of stronger intermolecular hydrogen bonds, which is accompanied by an increase in the strength characteristics and in the glass transition point of the ready material. The suggested mechanism of the formation of the regular three-dimensionally cross-linked structure of the multicomponent polyurethane and the revealed relationships between the rheokinetic parameters of the cold curing and the physicomechanical properties of the material synthesized in the presence of [(C4H9O)3P=O]2ZnCl2 have no analogs among the known polyurethane composites.

Synthesis of L-Lactide-Based Segmented Polyurethanes

ABSTRACTA series of segmented polyurethanes with polylactidediols soft segments and methylene-diphenyl-diisocyanate/1,4-butanediol hard segments with molecular weights in the range of 6.18 × 103 to 9.36 × 103 Da were synthesized. Stannous octoate was the catalyst for the reactions. These polymers were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, gel permeation chromatography, and thermogravimetric analyzer. Fourier transform infrared analyses revealed the formation of urethane groups and complete curing of polyurethane. The thermal degradation temperatures were in the range of 248.55–257.09°C. X-ray diffraction studies confirmed the segmented structure of polyurethanes.

Study on Microwave Curing of Polyurethane (PU)/Epoxy (EP) Interpenetrating Networks (IPN)

Microwave curing of PU/EP IPN was studied in this paper. Microwave curing IPN was prepared by means of intermittent microwave heating, The results indicates that microwave curing technique can shorten curing time remarkably. The microwave curing and thermal curing IPN have identical structure, tensile property of microwave curing IPN is better than that of thermal curing IPN, Impact strength of thermal curing IPN is slightly higher.

Structural Effect of Thiol-Compounds on the Thiol-Ene Based UV Curable Adhesive

Three thiol-compounds with different functionalities were synthesized through esterification reaction which was prepared by 1, 4-butanediol, trimethylolpropane, and pentaerythritol and 3-mercapto propionic acid respectively. Thiol-compounds and polyurethane-acrylate prepolymer were blended with addition of photo-initiator in certain proportions in order to form polyurethane curing film under UV irradiation. The structure and properties of the thiol-compounds and the polyurethane curing film were characterized by NMR, FT-IR, and TG. The results showed that the thiol-ene addition reaction between the urethane acrylates and the thiol-compounds was preceeded. With the increase of functionality of mercaptopropionic acid ester, the thermal stability improved, and the T-peel strength enhanced. When the moral ratio of urethane acrylates and trimethylolpropane-3-mercapto propionic acid ester was 1:1, the adhesive showed the best mechanical properties and thermal stability with curing time 40s, T-peel strength 88N/m and 50 % mass loss at 369°C, respectively.

Dynamic mechanical properties and structure of in situ cured polyurethane/hydrogenated nitrile rubber compounds: Effect of carbon black type

AbstractA peroxide‐curable hydrogenated nitrile rubber (HNBR) was modified by in situ crosslinked polyurethane (PU) in a 1 : 1 weight ratio. PU was formed from solid PU precursors, polyester polyol, and blocked polyisocyanate incorporated in the HNBR during the curing of the latter. HNBR/PU blends containing carbon black (CB) of different types (N234, N330, and N550) were prepared in this work. Thirty parts of CB per hundred parts of polymer matrix (HNBR and PU) were used. The curing of PU was followed by differential scanning calorimetry (DSC). Information of the phase structure was derived from DSC and dynamic mechanical analysis (DMA) tests. DMA results suggested that a quasi‐interpenetrating network structure developed in the HNBR/PU blend. This was confirmed also by scanning electron microscopy, transmission electron microscopy (TEM), and atomic force microscopy inspections. The partition of CB between the PU and HNBR was assessed by TEM. It was established that CB was exclusively located in the HNBR phase. CB N234 proved to be more efficient reinforcement than N330 and N550. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Reaction kinetics of toluene diisocynate and propanol by in situ FTIR

PurposeTo evaluate the effect of the concentrations of isocyanate group and hydroxyl group and hydroxyl group species on the rate constants of isocyanate‐propanol reaction, and to reveal the kinetics of isocyanate‐hydroxyl reaction.Design/methodology/approachThe in situ FTIR technique was employed to measure the group concentration evolutions, by which the rate constants were determined. Besides, the FTIR was used to detect the OH absorbance shifts during reaction and the OH absorbance at different concentrations. The kinetic mechanism of isocyanate‐propanol reaction was discussed with the combination of rate constants and FTIR spectra.FindingsA new reaction mechanism, alcohol association mechanism, was proposed that could explain many phenomena. It was revealed that the rate constant was independent of the isocyanate concentration, while the concentration and species of hydroxyl groups had apparent effects on the rate constants. It was possible to calculate the number averaged degree of association of propanol with alcohol association mechanism.Research limitations/implicationsThe associated n‐propanol molecules that reacted with isocyanate to form urethane were the associated dimer and trimer predominately, while the iso‐propanol was the dimer.Practical implicationsThe kinetics of isocyanate‐hydroxyl reaction and the alcohol association mechanism will be helpful to understand the preparation and curing of polyurethane, and their controls.Originality/valueA new reaction mechanism, alcohol association mechanism, was proposed that could explain many phenomena that might not be interpreted by other mechanisms. The mechanism could be employed to calculate the number averaged degree of association of alcohols.

A cross self‐curing system for an aqueous‐based PU hybrid

AbstractIsocyanate (NCO)‐terminated polyurethane (PU) prepolymer comprises carboxylic acid, which is obtained from a conventional PU preparation procedure. Aziridine‐terminated PU oligomer is prepared by an addition reaction of aziridine to NCO‐terminated PU prepolymer after it is neutralized with triethylamine. This PU oligomer is then dispersed with water and becomes a single‐component self‐curable aqueous‐based PU dispersion (PU‐AZ). PU carboxyl groups are not only the ionic centers stabilizing the aqueous polymer dispersion, but also serve as PU curing sites toward the curing reaction with its aziridine terminal groups on drying. This self‐curable PU‐AZ dispersion is miscible and compatible with other carboxyl groups containing aqueous‐based PU dispersion in any ratio, which results in a cross self‐cured PU hybrid formation on drying. This cross self‐cured PU hybridization process allows property modification and the curing of PU simultaneously without the addition of any external curing agent. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 550–558, 2005

Matching Cure Characteristics of Automotive Rubber Compound and Polyurethane Coating

The present investigation focuses on matching cure characteristics of EPDM rubber compound and polyurethane (PU) coating using temperature modulated and pressure differential scanning calorimetry (TMDSC, PDSC). TMDSC provides a detailed and better understanding of the curing process of model rubber system as well as complex automotive rubber compounds. The low level of unsaturation present in EPDM, results in the small heat of vulcanization (2–5 J g –1 ), which is difficult to accurately measure using conventional differential scanning calorimetry (DSC). Thus, curing of highly filled EPDM compound was investigated using TMDSC. The kinetics of PU curing was monitored using pressure DSC (PDSC), and heat of curing was determined as 4.2 J g –1 at 10°C min –1 heating rate. It is found that complex automotive compounds and the PU coating are curing simultaneously.

Aqueous-based polyurethane with dual-functional curing agent

Aqueous-based polyurethane (PU) with a carboxyl pendent group was prepared from a conventional PU prepolymer process. Its carboxyl group served as the ionic center for stabilizing the aqueous PU dispersion and as the curing site for post-curing reaction. A curing agent was synthesized from the substitution reaction of phosphorus oxychloride or phenylphosphonic dichloride by aziridine. Each compound consisted of two aziridinyl groups and the phosphorus composition. Its aziridinyl group reacted with a PU carboxyl group and its phosphorus content was introduced to this PU curing system simultaneously. Those compounds served as both curing agent and flame retardant for the PU curing system. The physical and mechanical properties of the resulting PU were improved corresponding to the curing dosage. The thermal properties and the flame inhibition behaviors of those post-cured PUs were evaluated by measurements using thermogravimetric analysis, dynamic mechanical thermal analysis, a limiting oxygen index, and a cone calorimeter.

Thermal and combustion behaviors of aqueous-based polyurethane system with phosphorus and nitrogen containing curing agent

Carboxyl group containing aqueous-based polyurethane (PU) is prepared by a conventional method. PU carboxyl group is the reactive site toward an aziridinyl containing post-curing agent for PU curing system. Two compounds are prepared from the substitutions of phosphorus oxychloride with aziridine (TAP) or then with N, N-diethylamine (DDP), respectively. TAP or DDP consists of three or two aziridinyl groups and also contains stable phosphorus-nitrogen bonds. It serves as a post-curing agent and a reactive flame retardant for the aqueous-based PU simultaneously. The mechanical and the physical properties of post-cured PU are modified corresponding to the curing dosage. The thermal stability of the resulted PU is improved and confirmed by thermogravimetric analyzer and dynamic mechanical thermal analyzer. Furthermore, the combustion behaviors of final PU are evaluated by the measurements of limiting oxygen index and cone calorimeter.

Convenient post-curing reactions for aqueous-based polyurethane anionomers

Anionic aqueous-based polyurethane (PU) dispersions were prepared by introducing carboxylic groups into a conventional PU backbone, followed by a water dispersion process. The resulting carboxylic groups containing aqueous-based PUs were amino-terminated anionomers. Two model reactions between an amino and a carboxylic group containing compounds with an epoxide and an aziridinyl compound, respectively were carried out at ambient temperature. Di-functional epoxide and aziridinyl compound were employed as the convenient single post-curing and dual-curing agents for these prepared PU dispersions. Di-aziridinyl compound was stable in aqueous PU dispersions as a latent curing agent when the pH value of the system was 8.0 or above. The curing behaviors of each PU curing system were monitored by measurements of the gel content, average particle size, zeta potential, and fluorescence spectra. The mechanical and thermal properties of these post-cured PUs were evaluated.

Polyurethane curing by a pulsed microwave field

The complete study of the crosslinking of polyurethane resins by means of a pulsed microwave field has been made, in order to describe the energy transfer processes in polymer films and to optimize the transfer efficiency. Experimental data show the energy transfer can be strongly enhanced by using specific pulse repetition frequencies which correspond to dielectric relaxation of polar structural elements in polymers. Moreover, the hardness of cured films can be also correlated with this pulse frequency specificity.

Curing of Polyurethane Pre‐polymers on Wool. I—Air, Press and Steam Curing

After application to woo) from organic solvent, isocyanate‐terminated polyurethane pre‐polymers are usually cured by exposure to the atmosphere for 4–8 days. The activity of the resin and the humidity of the atmosphere have an important effect on the rate of curing. Complete development of the shrink‐resisting effect can be achieved in 15 min or less by steam‐pressing or by exposure to saturated steam at 100d̀C. The suggested industrial procedures are to tumble in a dryer that has provision for open steam injection or to hang in a steam‐box. Reduction of the curing time by application of an organometallic catalyst with the resin tends to cause difficulties in maintenance of the solvent machine and in garment pressing.