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1.
Both liquid‐ and solid‐state carbon‐13–nuclear magnetic resonance (13C‐NMR) spectroscopies were used to investigate the cure acceleration effects of three carbonates (propylene carbonate, sodium carbonate, and potassium carbonate) on liquid and cured phenol‐formaldehyde (PF) resins. The liquid‐phase 13C‐NMR spectra showed that the cure acceleration mechanism in the propylene carbonate‐added PF resin seemed to be involved in increasing reactivity of the phenol rings, whereas the addition of both sodium carbonate and potassium carbonate into PF resin apparently resulted in the presence of ortho–ortho methylene linkages. Proton spin‐lattice rotating frame relaxation time (T1ρH) measured by solid‐state 13C cross polarization/magic‐angle spinning NMR spectroscopy was smaller for the cure‐accelerated PF resins than that of the control PF resin. The result indicated that the cure‐accelerated PF resins are less rigid than the control PF resin. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1284–1293, 2000 相似文献
2.
Low‐condensation phenol‐formaldehyde (PF) resins coreacted under alkaline conditions with up to 42% molar urea on phenol during resin preparation yielded PUF resins capable of faster hardening times than equivalent pure PF resins prepared under identical conditions and presented better performance than the latter. The water resistance of the PUF resins prepared seemed comparable to pure PF resins when used as adhesives for wood particleboard. Part of the urea was found by 13C‐NMR to be copolymerized to yield the alkaline PUF resin; whereas, especially at the higher levels of urea addition, unreacted urea was still present in the resin. Increase of the initial formaldehyde to phenol molar ratio decreased considerably the proportion of unreacted urea and increased the proportion of PUF resin. A coreaction scheme of phenolic and aminoplastic methylol groups with reactive phenol and urea sites based on previous model compounds work has been proposed, copolymerized urea functioning as a prebranching molecule in the forming, hardened resin network. The PUF resins prepared were capable of further noticeable curing acceleration by addition of ester accelerators; namely, glycerol triacetate (triacetin), to reach gel times as fast as those characteristic of catalyzed aminoplastic resins, but at wet strength values characteristic of exterior PF resins. Synergy between the relative amounts of copolymerized urea and ester accelerator was very noticeable at the lower levels of the two parameters, but this effect decreased in intensity toward the higher percentages of urea and triacetin. 13C‐NMR assignements of the relevant peaks of the PUF resins are reported and compared with what has been reported in the literature for mixed, coreacted model compounds and pure PF and urea‐formaldehyde (UF) resins. The relative performance of the different PUF resins prepared was checked under different conditions by thermomechanical analysis (TMA) and by preparation of wood particleboard, and the capability of the accelerated PUF resins to achieve press times as fast as those of aminoplastic (UF and others) resins was confirmed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 359–378, 1999 相似文献
3.
Effects of adding urea to the strand board core‐layer phenol–formaldehyde (PF) resin were investigated in conjunction with cure‐accelerating catalysts. Ten percent urea based on the liquid resin weight was added at the beginning, at three different middle stages of polymerization, and at the end of PF resin synthesis. No significant cocondensation between the urea and PF resin components occurred as identified by 13C NMR analyses, which corroborated well with the curing and strand board bonding performance test results. The various urea addition methods resulted in resins that slightly differ in the various tests due to the urea's temporary holding capacity of formaldehyde. The preferred method of urea addition was found to do it in the later part of PF resin synthesis for convenience, consistency, and slightly better overall performance. Some cure‐accelerating catalysts were shown to reduce the thickness swelling of strand boards. This study showed the usefulness of adding some urea to strand board core‐layer binder PF resins of replacing higher cost phenolic components with lower cost urea. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
4.
Yongsheng Zhang Zhongshun Yuan Chunbao Xu 《American Institute of Chemical Engineers》2015,61(4):1275-1283
The use of formaldehyde to prepare phenol‐formaldehyde (PF) resins is one of the primary challenges for the world‐wide PF industry with respect to both sustainability and human health. This study reports a novel one‐pot synthesis process for phenol‐5‐hydroxymethylfurfural (PHMF) resin as a formaldehyde‐free phenolic resin using phenol and glucose, and the curing of the phenolic resin with a green curing agent organosolv lignin (OL) or Kraft lignin (KL). Evidenced by 13C NMR, the curing mechanism involves alkylation reaction between the hydoxyalkyl groups of lignin and the ortho‐ and para‐carbon of PHMF phenolic hydroxyl group. The curing kinetics was studied using differential scanning calorimetry and the kinetic parameters were obtained. The OL/KL cured PHMF resins were tested in terms of thermal stability, and mechanical properties for their applications in fiberglass reinforced composite materials. The results obtained demonstrated that OL/KL can be promising curing agents for the PHMF resins. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1275–1283, 2015 相似文献
5.
The isomeric composition of several samples of resol‐type phenol formaldehyde resins used for silica–phenolic composites was evaluated by 1H‐ and 13C‐NMR spectroscopy and reverse‐phase HPLC techniques. The variations in the isomeric compositions were attributed to inadvertent variations in the process parameters. A mathematical relation was determined for calculation of free phenol from 1H‐NMR measurements. The samples were cured at 160°C for 8 h in an inert atmosphere of N2. The extent of cure in the hardened samples was measured by FTIR analysis. The effect of isomeric composition on the extent of cure was studied. Free phenol and p‐hydroxymethyl phenol, exhibiting a linear correlation, were found to have a pronounced effect on the extent of cure. The cure kinetics were derived by dynamic DSC measurements. Activation energy (E) for curing exhibited a near linear correlation independently with free phenol content and the extent of cure. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2517–2524, 2003 相似文献
6.
Novolak‐type phenol‐formaldehyde (PF) resins with solution form were prepared by reacting phenol‐liquefied Cryptomeria japonica (Japanese cedar) wood with formalin in the presence of methanol. Wood powders of Albizzia falcate (Malacca albizzia) impregnated with these resins were air dried followed by an oven‐dried at 60°C. DSC analysis showed the PF resin existing in wood powders could be melted, and could be cured if hexamine was mixed and heated at high temperature. Compression‐molded plates made with PF resin impregnated woods had a high degree of curing reaction. However, compression‐molded plates hot‐pressed at 180°C for 8 min or 200°C for 5 min had better internal bonding strength and dimensional stability than others. Premixing hexamine with PF resin and impregnating into wood powders simultaneously could enhance the reactivity of PF resin, but it was not useful for improving the properties of compression‐molded plates. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
7.
Matrix assisted laser desorption ionization time of flight (MALDI‐ToF) mass spectrometry has consistently confirmed on a number of PUF resins that phenol–urea cocondensates exist in phenol–urea–formaldehyde (PUF) resins. A noticeable proportion of methylene‐linked phenol to urea cocondensates were detected in all the PUF resins tried, alongside methylene bridges connecting phenol to phenol and urea to urea. The PUF, PF, and UF oligomers formed were identified. Variations of the PUF preparation procedure did always yield a certain proportion of the mixed phenol to urea cocondensates. Their relative proportion was determined and related the synthesis procedure used. Comparison of the MALDI‐ToF results with a 13C NMR investigation showed that in a real PUF resin in which phenol to urea cocondensates were identified the methylene bridge NMR signal at 44 ppm, characteristic of phenol to urea unsubstituted model compound cocondensates, does not appear at all. This confirmed that this peak cannot be taken as an indication of the existence of phenol and urea condensation under actual resin preparation conditions. The peak indicating cocondensation in PUF resins in which the phenolic nuclei and urea are substituted appears instead at 54.7–55.0 ppm. Thermomechanical analysis has again confirmed that the resin gel times greatly accelerates with increasing urea molar content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
8.
A series of UF resins and one MUF resin were studied by low‐resolution 1H‐NMR. The mobility of the resin during curing could be followed by measuring the spin‐spin relaxation time (T2) with curing time. The relative curing behavior was similar to that found by traditional gel time measurements. In addition, extra features in the T2 plots with curing time showed at what point the bulk of the condensation reactions took place. The speed of cure was also related to the chemical groups in the liquid resin, and it was found that the linear methylol groups were mainly responsible for the curing speed of the resins. By studying the curing with different hardener levels and glue concentrations it was found that a UF resin is more sensitive to the glue mix concentration than an MUF resin. A cured resin was also studied after curing to investigate postcuring effects. Water seemed to play the biggest role in the postcure, with substantial amounts present immediately after cure, which decreased with curing time and aging. For the low mol ratio resins studied here further curing reactions did not seem to play a major role in the post curing phenomenon. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 754–765, 2000 相似文献
9.
Phenol‐urea‐formaldehyde (PUF) resins were synthesized by reacting mixture of methylolureas (MMU), phenol, and formaldehyde. The structure of PUF cocondensed resins at different stages of reaction were analyzed by liquid 13C nuclear magnetic resonance (NMR) spectroscopy. The liquid 13C‐NMR analysis indicated that methylolureas had the dominant content in MMU with the reaction between urea and formaldehyde under the alkaline condition. The PUF cocondensed resins had no free formaldehyde. methylolureas were well incorporated into the cocondensed resins by reacting with phenolic units to form cocondensed methylene bridges. The second formaldehyde influenced the further reaction and the structure of the PUF resins. The resins with the prepared method of PUFB possessed relatively high degree of polymerization and low proportion of unreacted methylol groups. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
10.
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 相似文献
11.
2‐Hydroxymethylphenol (2‐HMP) and 4‐hydroxymethylphenol (4‐HMP) were used as model compounds to study the reactions that occur during cure of phenol–formaldehyde (PF) resin to which cure accelerators (ethyl formate, propylene carbonate, γ‐butyrolactone, and triacetin) have been added. The addition of cure accelerators significantly increased the rate of condensation reactions. The cure accelerators were consumed during the reaction, indicating that they do not act as true catalysts. Major dimeric and trimeric reaction products were isolated and their structures determined. The results are consistent with a mechanism in which the hydroxymethyl group of 2‐HMP (or 4‐HMP) is first transesterified by the cure accelerator. The ester group is then displaced by reaction with the negatively charged ortho or para position of a second molecule (SN2 mechanism) or is converted to a reactive quinone methide intermediate, which subsequently reacts with the negatively charged ortho or para position of a second molecule (quinone methide mechanism). When accelerators were added to the reaction mixture, the self‐condensation of 2‐HMP was faster than that of 4‐HMP. As is well documented in the literature, the exact opposite is true without added accelerators. This result would seem to indicate that the phenolic oxygen helps activate the esterified ortho‐hydroxymethyl group. The number and nature of crosslinks in a PF resin cured with added cure accelerator might be different than those in a PF resin cured without an added cure accelerator. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3256–3263, 2002 相似文献
12.
Guanidine carbonate is shown to be an accelerator of phenol‐formaldehyde (PF) resins that while yielding slightly slower gel times than triacetin when added to a PF resin glue mix, is also capable of giving glue‐mix pot lives on the order of several days. Hence, this is long enough to be premixed with the resin long before use. Both triacetin and guanidine carbonate used as simple glue‐mix additives are shown to increase the ultimate strength of the resin bond, whatever the length of the curing time used for the purpose. This is shown by thermomechanical analysis and the application to wood particleboard. Triacetin is shown to be usable during PF resin preparation rather than just being added to the glue mix, yielding better resins capable of giving higher bond values without a great acceleration of the geling of the resin itself. The mechanisms involved in the acceleration of PF resins introduced by both compounds appears to be based on facilitating reactions of crosslinking involving carbonic acid ions present in the resin solution. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 249–259, 2000 相似文献
13.
A. Pizzi 《应用聚合物科学杂志》1999,71(10):1703-1709
Wide‐scope mathematical relationships have been established between the 13C‐NMR of liquid polycondensation resins, such as urea–formaldehyde and phenol–formaldehyde resins, and the strength of the network formed by the same resin when hardened under well‐defined conditions, the thermomechanical analysis deflection, the number average molecular mass and the number of degrees of freedom of the average polymer segment between crosslinking nodes in the hardened resin network, the resin network glass transition temperature, its solid‐phase 13C‐NMR proton‐rotating frame spin‐lattice relaxation time, and the homogeneous and heterogeneous polymer segment/polymer segment interfacial interaction energy calculated by molecular mechanics. These mathematical relationships allow the calculation of any of these parameters from any of the techniques listed, provided that all of the systems are used under well‐defined conditions. Under different conditions, the values of the numerical coefficients involved change; and, whereas the equations are still valid, a different set of coefficients needs to be recalculated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1703–1709, 1999 相似文献
14.
Six types of phenolic foaming resins were synthesized at room temperature with different formaldehyde/phenol (F/P) ratios in this study. The effects of F/P ratios on physicochemical characteristics and foaming properties of the resulting resins were analyzed based on viscosity, solids content, hydroxymethyl index, residual monomer content, molecular structure of the foaming resin, flame retardancy, and foam compression strength measurements. The results of the present study indicated that viscosity and solids content of the foaming resins increased with an increase in F/P; the hydroxymethyl index of the resin first increased and then decreased with an increase in F/P, reaching its maximum at F/P = 1.6; the trimer, tetramer, and pentamer contents of the resins increased with an increase in F/P. Nuclear magnetic resonance (13C NMR) spectral analysis indicated that the presence of para/para‐methylene, para‐hydroxymethyl, and ortho‐hydroxymethyl groups in the resin gradually increased with an increase in F/P; the proportions of ortho/ortho‐ and ortho/para‐methylene bonds of the resin increased as F/P was increased. The increase in F/P was demonstrated to be conducive to improving the compression strength, thermal stability, and flame retardancy of the phenolic foam and reducing its peak heat release rate and total smoke release. The morphology of phenolic foams show that the closed cell content in the PF foam increases with the F/P ratio until it reaches a ratio of 1.6. Furthermore, the cell size becomes more uniform. POLYM. COMPOS., 36:1531–1540, 2015. © 2014 Society of Plastics Engineers 相似文献
15.
A series of fluorine‐containing bismaleimide (FBMI) monomers are synthesized by a 3‐step reaction for using as the applications of low‐k materials. The synthesized FBMI monomers are characterized by the 1H, 13C, 19F nuclear magnetic resonance (NMR) spectroscopy and element analysis. These FBMI monomers react with free radical initiator or self‐cure to prepare FBMI‐polymers. All the self‐curing FBMI resins have the glass transition temperatures (Tg) in the range of 128–141°C and show the 5% weight loss temperatures (T5%) of 235–293°C in nitrogen atmosphere. The higher heat resistance of self‐curing FBMI resin relative to FBMI‐homopolymer is due to its higher crosslinking density. The FBMI resins exhibit improved dielectric properties as compared with commercial bismaleimide (BMI) resins with the dielectric constants (Dk) lower than 2.49, which is related to the low polarizability of the C? F bond and the large free volume of CF3 groups in the polymers. Besides, the flame retardancy of all these FBMI resins could be enhanced via the introduction of Br‐atom. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
16.
A method based on the use of 13C-NMR relative peak intensity ratios for different characteristic chemical groups, known or supposed to contribute to phenol–formaldehyde (PF) resin strength and formaldehyde emission is presented. The method relates results obtained by 13C-NMR analysis of liquid PF resins with the strength and formaldehyde emission in the resin-hardened state. Correlation of differnt peak ratio with experimental results allows the proposal of equations relating the sum of different 13C-NMR peak ratios with the two mentioned physical properties of the same resins in their hardened state. The equations presented appear to have some applied value in predicting physical properties of hardened industrial-type PF resins from a single 13C-NMR spectrum of the original liquid resin, as well as to render easier comparison between different PF resin formulations. © 1995 John Wiley & Sons, Inc. 相似文献
17.
Renewable chemicals are of growing importance in terms of opportunities for environmental concerns over fossil‐based chemicals. Lignocellulosic biomass can be converted into energy and chemicals via thermal and biological processes. Among all the transformation processes available, fast pyrolysis is the only one to produce a high yield of a liquid‐phase product called bio‐oil or pyrolysis oil. Bio‐oil is considered to be a promising substitute for phenol in phenol formaldehyde (PF) resin synthesis. In this work, bio‐based phenolic resins have been formulated, partially substituting phenol by bio‐oils from two Canadian whole‐tree species. The new resins are produced by replacing 25, 50, and 75% of phenol with bio‐oil for each species (three bioresins per species). The aim of this study is to synthesize renewable resins with competitive price and satisfactory quality. The results obtained have shown that substitution degree up to 50% provided reactivity and performance equal or superior to the pure PF resin. They also present a good storage stability, improved shear strength, and thermal stability comparable to the pure PF. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40014. 相似文献
18.
This study was conducted to investigate the effects of reaction pH condition and hardener type on the reactivity, chemical structure, and molecular mobility of urea–formaldehyde (UF) resins. Three different reaction pH conditions, such as alkaline (7.5), weak acid (4.5), and strong acid (1.0), were used to synthesize UF resins, which were cured by adding four different hardeners (ammonium chloride, ammonium sulfate, ammonium citrate, and zinc nitrate) to measure gel time as the reactivity. FTIR and 13C‐NMR spectroscopies were used to study the chemical structure of the resin prepared under three different reaction pH conditions. The gel time of UF resins decreased with an increase in the amount of ammonium chloride, ammonium sulfate, and ammonium citrate added in the resins, whereas the gel time increased when zinc nitrate was added. Both FTIR and 13C‐NMR spectroscopies showed that the strong reaction pH condition produced uronic structures in UF resin, whereas both alkaline and weak‐acid conditions produced quite similar chemical species in the resins. The proton rotating‐frame spin–lattice relaxation time (T1ρH) decreased with a decrease in the reaction pH of UF resin. This result indicates that the molecular mobility of UF resin increases with a decrease in the reaction pH used during its synthesis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2677–2687, 2003 相似文献
19.
Jianxiang Huang Liqiang Wan Jian Zhang Fei Gao Jianjun Tian Farong Huang Lei Du 《应用聚合物科学杂志》2009,114(3):1725-1730
4,4′‐Diazidomethylbiphenyl (DAMBP) and poly(dimethylsilylene‐ethynylenephenyleneethynylene) (PDMSEPE) were thermally polymerized to form a novel silicon‐containing polytriazole resin (PDMSEPE‐DAMBP) by 1,3‐dipolar cycloaddition. Differential scanning calorimetry, FTIR, and 13C‐NMR were used to characterize the curing behaviors of PDMSEPE‐DAMBP resins. The results indicated that the resins could cure at temperatures as low as 80°C. Dynamic mechanical analysis showed that there was a glass transition at 302°C for the cured PDMSEPE‐DAMBP resin. The carbon fiber (T700) reinforced PDMSEPE‐DAMBP composites exhibited excellent mechanical properties at room temperature and high property retention at 250°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
20.
Amy Philbrook Scott Earnshaw Christopher J. Easton Max A. Keniry Melissa J. Latter 《应用聚合物科学杂志》2013,128(5):3375-3381
1H‐15N‐13C correlation NMR spectroscopy techniques developed to identify and characterize co‐polymer fragments in melamine‐urea‐formaldehyde (MUF) and phenol‐urea‐formaldehyde (PUF) model systems have been applied to industrially prepared MUF, PUF, and phenol‐melamine‐formaldehyde (PMF) resins. The NMR data confirm that co‐polymers form in a commercially prepared MUF resin manufactured by Momentive Specialty Chemicals Pty. Ltd. Spectra from PUF model reactions were compared with those from a PUF resin and it was determined that PUF co‐polymers did not form in the resin prepared using typical temperature and pH. Finally, NMR spectroscopy was used to identify and characterize PMF co‐polymer bonds in a phenol‐melamine‐urea‐formaldehyde (PMUF) resin prepared using a procedure from Momentive Specialty Chemicals Pty. Ltd. With these NMR techniques in hand, it is now possible to relate co‐polymer structures to properties of commercial thermosets. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献