Influence of acrylamide copolymerization of urea–formaldehyde resin adhesives to their chemical structure and performance

To lower the formaldehyde emission of wood‐based composite panels bonded with urea–formaldehyde (UF) resin adhesive, this study investigated the influence of acrylamide copolymerization of UF resin adhesives to their chemical structure and performance such as formaldehyde emission, adhesion strength, and mechanical properties of plywood. The acrylamide‐copolymerized UF resin adhesives dramatically reduced the formaldehyde emission of plywood. The ¹³C‐NMR spectra indicated that the acrylamide has been copolymerized by reacting with either methylene glycol remained or methylol group of UF resin, which subsequently contributed in lowering the formaldehyde emission. In addition, an optimum level for the acrylamide for the copolymerization of UF resin adhesives was determined as 1%, when the formaldehyde emission and adhesion strength of plywood were taken into consideration. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Comparative 13C‐NMR and matrix‐assisted laser desorption/ionization time‐of‐flight analyses of species variation and structure maintenance during melamine–urea–formaldehyde resin preparation

The preparation of an industrially used sequential formulation of a melamine–urea–formaldehyde resin was followed by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry and ¹³C‐NMR analysis. The analysis allowed us to identify and follow the appearance, increase, decrease, and disappearance of a multitude of chemical species during the preparation of both the initial urea–formaldehyde (UF) phase of the reaction and the subsequent reaction of melamine with the UF resin that formed. The analysis indicated that (1) the increase and decrease in the species that formed proceeded through a cycle of the formation and degradation of species occurring continuously through what appeared to be a series of complex equilibria, (2) even at the end of the reaction a predominant proportion of methylene ether bridges was still present, (3) some small proportion of methylene bridges already had formed in the UF reaction phase of the resin even under rather alkaline conditions, and (4) the addition of melamine to the UF prepolymer induced some noticeable rearrangement of methylene ether bridges to methylene bridges. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Blends of natural rubber and polyurethane latices studied by 1H wideline and 13C MAS solid‐state NMR

¹H wideline and ¹³C magic‐angle spinning NMR have been used to study the morphology and dynamics of latex‐cast and solution‐cast film blends of natural rubber (NR) and a polyurethane (PU) based on poly(?‐caprolactone) diol and isophorone di‐isocyanate. ¹H T₁ and T_1ρ relaxation times have been measured, and the extent of interpenetration of the NR and PU constituents has been monitored using the Goldman–Shen technique. The NMR spectra and relaxation properties indicated that the NR and PI constituents largely occupy separated domains on a distance scale of >10 nm. The Goldman–Shen experiments indicated that there was slightly greater contact between NR and PU in the solution‐cast samples than in the latex‐cast. The tensile properties of the films have been measured. The tensile strength and initial Young's modulus pass through a maximum at a PU content of about 50 wt%. © 2002 Society of Chemical Industry     

Differential scanning calorimetry of urea–formaldehyde adhesive resins,synthesized under different pH conditions

The purpose of this study was to investigate the effects of reaction pH conditions on thermal behavior of urea–formaldehyde (UF) resins, for the possible reduction of formaldehyde emission of particleboard bonded with them. Thermal curing properties of UF resins, synthesized at three different reaction pH conditions, such as alkaline (pH 7.5), weak acid (pH 4.5), and strong acid (pH 1.0), were characterized with multiheating rate method of differential scanning calorimetry. As heating rate increased, the onset and peak temperatures increased for all three UF resins. By contrast, the heat of reaction (ΔH) was not much changed with increasing heating rates. The activation energy (E_a) increased as the reaction pH decreased from alkaline to strong acid condition. The formaldehyde emission of particleboard was the lowest for the UF resins prepared under strong acid, whereas it showed the poorest bond strength. These results indicated that thermal curing behavior was related to chemical species, affecting the formaldehyde emission, while the poor bond strength was believed to be related to the molecular mobility of the resin used. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 422–427, 2006     

13C solid‐state NMR analysis of the DGEBA/TETA epoxy system

Mechanical properties measurements, like Charpy impact tests, provided evidence that the macromolecular network of the epoxy system formed by the hexafunctional triethylene tetramine hardener, TETA, with the diglycidyl ether of bisphenol A monomer, DGEBA, can be modified by changing the hardener content. The previously analyzed monomer‐to‐hardener ratios were here studied by ¹³C‐NMR solid state techniques. The results from crosspolarization/magic angle spinning (CPMAS) ¹³C‐NMR spectra, together with the evaluation of proton spin‐lattice relaxation time in the rotating frame (Tρ), display the behavior of these epoxy/hardener mixtures considering the mobility and interaction of molecular segments present at the macromolecular structure. The results also show that the epoxy‐rich mixtures form tight, and therefore brittle, structures as previously observed by mechanical tests. The stoichiometric monomer‐to‐hardener ratio is a transition point where an increase in the mobility was found. For the amine‐rich mixtures the obtained results suggest the presence of domains with different segmental mobilities. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2358–2362, 2000     

13C‐NMR study on the structure of phenol‐urea‐formaldehyde resins prepared by methylolureas and phenol

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     

Synthesis–structure–performance relationship of cocondensed phenol–urea–formaldehyde resins by MALDI‐ToF and 13C NMR

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     

Structural changes of bulk polyethylene by stress impact as studied by solid‐state NMR

Solid‐state ¹³C‐ and ¹H‐NMR spectra of bulk high‐density polyethylene samples, cylindrical in form, to which stress impacts were applied with a home‐made stress‐impact apparatus, were measured. The fraction of the noncrystalline component increases with an increase in the stress‐impact strength. In the crystalline region, the monoclinic crystalline component appear with the stress impact, in addition to the major orthorhombic crystalline component. Furthermore, dynamic characterization was carried out on the basis of the observed values of the relaxation parameters ¹H T₂ and T_CH of the ¹H and ¹³C nuclei. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2268–2272, 2001     

Examination of selected synthesis and room‐temperature storage parameters for wood adhesive‐type urea–formaldehyde resins by 13C‐NMR spectroscopy. V

The effects of posttreatments of particleboard adhesive‐type urea–formaldehyde resins were studied. The resins were synthesized with formaldehyde/first urea (F/U₁) mol ratios of 1.40, 1.60, 1.80, 2.10, and 2.40 and then the second urea was added to give a final formaldehyde/urea ratio of 1.15 in alkaline pH. The resins were posttreated at 60°C for up to 13.5 h and the 2.5‐h heat‐treated resin samples were stored at room temperature for up to 27 days. Resins sampled during the posttreatments were examined by ¹³C‐NMR and evaluated by bonding particleboards. In the posttreatments, hydroxymethyl groups on the polymeric resin components dissociated to formaldehyde and reacted with the second urea, and methylene and methylene–ether groups were formed from reactions involving the second urea. Methylene–diurea and urea groups bonded to UF polymers were identified. As a result, the viscosity of the resins initially decreased but later increased along with the cloudiness of the resins. Bond‐strength and formaldehyde‐emission values of particleboard varied with posttreatment variables as well as with the F/U₁ mol ratios used in the resin syntheses. The results would be useful in optimizing resin synthesis and handling parameters. Various reaction mechanisms were considered. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1896–1917, 2003     

Structure of resorcinol,phenol, and furan resins by MALDI‐TOF mass spectrometry and 13C NMR

The structure of traditional, linear phenol–resorcinol–formaldehyde (PRF) resins, urea‐branched PRF resins, and phenol–resorcinol–furfural (PRFuran) resins has been investigated in depth by both matrix‐assisted laser desorption/ionization time of flight (MALDI‐TOF) mass spectroscopy and ¹³C NMR. The structure of a variety of oligomers has been obtained, and the structures present in each of the three types of resins related to the very different percentages of resorcinol needed for their equal performance as adhesives. The oligomers type and species distribution appeared very different for each case. PRF resins performance is improved by maximizing either the proportion of resorcinol‐containing oligomers or methylol‐groups containing oligomers, even without any resorcinol, or both. It is equally obtained by the minimization of the relative proportion of the low reactivity Phenol (CH₂ Phenol) species in which resorcinol is not present, this being the most important parameter. This can be obtained by more effective use of the resorcinol by just modifying the resin manufacturing procedure. This parameter instead does not appear to be determinant in PRFuran resins. In these, it is the higher molecular weight of furfural in relation to formaldehyde that engenders for the same manufacturing procedure a correspondingly lower proportion of resorcinol in the resin. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2665–2674, 2004     

Fibrous long‐chain organic acid cellulose esters and their characterization by diffuse reflectance FTIR spectroscopy,solid‐state CP/MAS 13C‐NMR,and X‐ray diffraction

Unsaturated and saturated organic acids with 11 and 18 carbon atoms, respectively, were used in a heterogeneous esterification reaction in the pyridine/toluene sulfonyl chloride system to prepare fibrous cellulose esters with different degrees of substitution. Highly bleached sulfite cellulose fibers were esterified during a 1‐ or 2‐h reaction time with the following organic acids: undecylenic acid, undecanoic acid, oleic acid, and stearic acid. In all cases, the heterogeneous esterification yielded partially substituted cellulose esters retaining their fibrous structure. The substitution reaction was confirmed by diffuse reflectance infrared spectroscopy and the chemical structures of cellulose esters were identified by solid‐state CP/MAS ¹³C‐NMR (75.3 MHz). X‐ray diffraction analyses showed broadening of the diffraction peaks with a higher degree of substitution of cellulose esters, which suggests structural changes within the cellulose fibers. Because the broadening peaks of X‐ray spectra or the unassigned C‐4 region of substituted cellulose chains in NMR spectra do not allow the calculation of dimensional changes of cellulose crystallites in cellulose esters, the lateral dimensions of crystallites in only cellulose fibers were calculated. The value derived from NMR (4.6 nm) differs by about 11% when compared with the value calculated from X‐ray diffraction data (4.1 nm). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1354–1365, 2000     

Acetals‐induced strength increase of melamine–urea–formaldehyde (MUF) polycondensation adhesives. II. Solubility and colloidal state disruption

The strength improvement induced by addition of acetals such as methylal and ethylal in melamine–urea–formaldehyde (MUF) resins could be mostly ascribed to the increased effectiveness and participation of the melamine to resin cross‐linking. This phenomenon has been shown here, by matrix‐assisted laser desorption/ionization time of flight (MALDI‐TOF) mass spectroscopy, resin aging time stability, and mainly by laser light scattering, to be due to the following: (i) the increased solubility in water afforded by the acetals cosolvents of both the unreacted melamine and of the normally very much lower solubility, higher molecular weight, lower methylolated oligomers fraction, this leading to preferentially homogeneous and hence more effective reaction rather than heterogeneous reactions; and (ii) the effect that such acetals have on the size distribution of the resin colloidal particles, with the presence of acetals such as methylals markedly decreasing the average colloidal particles diameter of the resin. This latter effect appears to be due to the disruption of the molecular clustering of the MUF resin colloidal particles, but rearrangements in the size of the colloidal particles due to the decrease in surface tension of the system, which has also been noted, cannot be excluded. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1855–1862, 2002     

Examination of selected synthesis parameters for wood adhesive‐type urea–formaldehyde resins by 13C NMR spectroscopy. III

The varying polymer structures of wood adhesive‐type urea–formaldehyde resins resulting from different formaldehyde/first urea (F/U₁) mole ratios used in the first step of resin manufacture were investigated using ¹³C. As the F/U₁ mole ratio decreased progressively from 2.40 to 2.10 and to 1.80, the viscosity increase due to polymerization during resin synthesis became faster and resulted in decreasing side‐chain branches and increasing free urea amide groups in the resin structure. The resultant UF resins, with the second urea added to an overall F/(U₁ + U₂) of 1.15, showed viscosity decreases when heated with stirring or allowed to stand at room temperature that were also characteristic with the F/U₁ mole ratios used in resin synthesis. The formaldehyde emission levels of particleboards bonded with the freshly made UF resins showed relatively small but similarly characteristic variations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2800–2814, 2001     

Study on the spin probe‐added polymeric dense membranes by 13C solid‐state nuclear magnetic resonance spectroscopy

This article is a duplicate of an article previously published in the Journal of Applied Polymer Science, Vol. 99, No. 6, March 15, 2006, pp. 3062‐3069 http://doi.wiley.com/10.1002/app.22908 . We regret any inconvenience this may have caused.     

Structural analysis of oriented poly(ε‐caprolactone) including CaCO3 particles with 13C solid‐state NMR

The results of a study of the relation between the oriented structure and drawn Poly(ε‐caprolactone) specimens including CaCO₃ particles and their dynamic mechanical properties are presented. The loss elasticity, E″, showed almost the same curve for both undrawn sheets and drawn sheets as a function of CaCO₃ content. On the other hand, the storage modulus, E′, of drawn sheets increased nonlinearly with increasing CaCO₃ content, and their curve showed lower E′ values than those of undrawn sheets. By simulation of ¹³C CP NMR spectra of drawn PCL/CaCO₃ sheets, both oriented and unoriented components were observed. The distribution parameter, p, of drawn PCL/CaCO₃ sheets was 13°, which was larger than those (8°) of drawn PCL. Further, the fraction of the unoriented component increased with increasing CaCO₃ content. Thus, adding CaCO₃ particles into the PCL, the arrangement of the oriented component was disturbed and decreased. In addition, from the line shape analyses of ¹³C CP MAS NMR spectra, four peaks were obtained in not only undrawn sheets but also in drawn sheets of both PCL and PCL/CaCO₃ compounds. Besides, structural change occurred at only drawn PCL/CaCO₃ sheets. Therefore, the change in dynamic mechanical properties observed only for drawn PCL/CaCO₃ sheets were strongly dependent on the orientational structure, which was formed under shear stress of the stretching drawn process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2376–2382, 2001     

13C‐NMR study on cure‐accelerated phenol–formaldehyde resins with carbonates

Both liquid‐ and solid‐state ¹³C‐NMR spectroscopies were employed to investigate the cure‐acceleration effects of three carbonates [propylene carbonate (PC), sodium carbonate (NC), and potassium carbonate (KC)] on liquid and cured phenol–formaldehyde (PF) resins. The liquid‐phase ¹³C‐NMR spectra showed that the cure‐acceleration mechanism in the PC‐added PF resin seemed to be involved in increasing reactivity of the phenol rings, while the addition of both NC and KC into PF resin apparently resulted in the presence of ortho–ortho methylene linkages. Proton spin‐lattice rotating frame relaxation time (T_1ρH) measured by solid‐state ¹³C‐CP/MAS‐NMR spectroscopy was smaller for the cure‐accelerated PF resins than for that of the control PF resin. The result indicated that cure‐accelerated PF resins are less rigid than the control PF resin. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 841–851, 2000     

Hydrogen bonding effect on the poly(ethylene oxide), phenolic resin,and lithium perchlorate–based solid‐state electrolyte

The interaction behavior of solid‐state polymer electrolytes composed of poly(ethylene oxide) (PEO)/novolac‐type phenolic resin and lithium perchlorate (LiClO₄) was investigated in detail by DSC, FTIR, ac impedance, DEA, solid‐state NMR, and TGA. The hydrogen bonding between the hydroxyl group of phenolic and ether oxygen of the PEO results in higher basicity of the PEO. The higher basicity of the ether group can dissolve the lithium salts more easily and results in a greater fraction of “free” anions and thus higher ionic conductivity. DEA results demonstrated that addition of the phenolic increases the dielectric constant because of the partially negative charge on the ether group induced by the hydrogen bonding interaction between ether oxygen and the hydroxyl group. The study showed that the blend of PEO(100)/LiClO₄(25)/phenolic(15) possesses the highest ionic conductivity (1.5 × 10^?5 S cm^?1) with dimensional stability. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1207–1216, 2004     

Morphology and molecular mobility of plasticized polylactic acid studied using solid‐state 13C‐ and 1H‐NMR spectroscopy

MAS ¹³C‐NMR measurements were used for the study of morphology and molecular mobility in amorphous quenched and triacetine‐plasticized PLA samples and PLA samples which underwent cold crystallization during annealing at 80 and 100 °C. The single pulse MAS ¹³C‐NMR spectra indicate that plasticizer promotes cold crystallization which results in the decrease of the temperature of crystallization and formation of more perfect crystalline domains. The T₁(¹³C) spin‐lattice relaxation times show that the presence of plasticizer molecules leads to an increase of local mobility in PLA chains but plasticized PLA after annealing at 100 °C shows more rigid structure. The series of broad line ¹H‐NMR spectra performed at temperatures up to 100 °C provided information on the changes in relaxation processes and morphology of the studied samples. The interpretation of the results obtained using the techniques of NMR spectroscopy were supported by WAXD and DSC measurements. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43517.     

Thermal history driven molecular structure transitions in alumino‐borosilicate glass

The glass network structure governs various thermos‐physical properties such as viscosity, thermal, and electrical conductivities, and crystallization kinetics. We investigated the effect of temperature on structural changes in a Na₂O‐CaO‐Al₂O₃‐SiO₂‐B₂O₃ glass system using ²⁷Al MAS NMR spectroscopy. Around the glass transition temperature, most of aluminate structures exist as AlO₄, acting as a glass former. When the temperature is above the melt crystallization temperature, the AlO₄ structure is drastically decreased and glass structures are mainly composed of AlO₅ and AlO₆, acting as glass modifiers. Thermodynamic assessment based on Gibbs energy minimization was used to confirm the dependency of aluminate structure's amphoteric characteristic on temperature by calculating the site fraction of aluminate molecular structures at different temperatures. Temperature‐induced aluminate structural variation can also influence silicate and borate structural changes, which have been confirmed by the ²⁹Si and ¹¹B NMR spectra.