Cross-linking of amidated polybutadiene with resole. II.

To prove the main cross-linking reaction between amidated polybutadiene and resole, cross-condensation reactions involving simple amide compounds and resole were examined. Amide compounds having both an amide group and a carboxylic acid group inhibited the self-condensation of resole itself. The cross-condensation products obtained from succinamic acid and 2-methylolphenol were separated using a preparative chromatography method to identify the cross-condensed products in which the main products were cross-condensed oligomers having an imide linkage. A cross-condensation scheme was proposed, and it was concluded that the main cross-linking reaction between amidated polybutadiene and resole also followed the same scheme.     

Thermal cure monitoring of phenolic resole resins based on in situ fluorescence technique

The thermal curing reaction of two phenolic resole resins is monitored using the fluorescence technique. The intrinsic fluorescence can be used as an indicator for cure monitoring for the first resole. As the thermal curing proceeds, the intrinsic fluorescence intensity of the resole resin decreases and exhibits a few nanometers of redshift. The fluorescence intensity of the emission maxima is correlated with the conversion measured by differential scanning spectroscopy. A linear correlation is found at three different temperatures. The intrinsic fluorescence cannot always be used for monitoring the curing process of phenolic resole resins. Thus, three intramolecular charge transfer compounds and two organic donor–π‐acceptor salts are selected and applied for the cure monitoring of the second phenolic resole resin. As the curing reaction proceeds, the fluorescence emission spectra of the probes exhibit a blue spectral shift and the intensity changes because of environmental changes. An intensity ratio method is applied in which the ratios of the low‐ to high‐intensity changes in the emission bands are used to determine the degree of the curing process. There is a smooth correlation between the intensity ratio method and the degree of cure. The method enables one to follow the changes in the polymer structure at low and intermediate degrees of the curing process (below 70%) and obtain comparable results from different types of probes during the same curing process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1773–1780, 2002     

淀粉基生物质胶粘剂的固化与性能研究

将淀粉在硫酸作用下水解的产物用于替代甲醛与苯酚进行缩聚反应生成淀粉基酚醛树脂,然后以六次甲基四胺为固化剂进行交联固化。研究了淀粉基酚醛树脂的凝胶时间、固化反应表观活化能、冲击强度、热失重性能与断面形貌,并与甲醛基酚醛树脂性能进行比较。结果表明,淀粉基酚醛树脂的固化反应表观活化能为19.8kJ/mol,冲击强度为741J/m2,600℃质量残留率为40%,具有良好的耐热性能,游离甲醛质量分数仅为0.4%,大大低于常规酚醛树脂的甲醛含量。     

Addition curable phenolic resins based on ethynyl phenyl azo functional novolac

Novel addition curable phenolic resins bearing terminal ethynyl groups anchored to benzene ring through a phenyl azo linkage were realized by the coupling reaction between novolac and 3-ethynyl phenyl diazonium salt. The diazo-coupling occurred to a maximum of 50 mol%. The apparent molecular weight, determined from gel permeation chromatography showed a downward drift with increase in degree of acetylene substitution. The resin underwent curing in a broad temperature range 140-240 °C. Analyses using a model compound indicate that the curing occurs via various addition polymerization of acetylene groups. The thermal stability and anaerobic char yield of the polymers increased proportional to the crosslinking and were considerably superior to those of a conventional resole. Isothermal pyrolysis studies implied the possibility for the decomposition occurring mainly by loss of nitrogen gas, and hydrocarbon to form mostly an amorphous char.     

Partners sought for UV catalyst development

THE CREATOR of an ultraviolet (UV) light activated catalyst for curing liquid phenolic resole resins is looking for industry partners to further develop his technology.This is a short news story only. Visit www.reinforcedplastics.com for the latest plastics industry news.     

C NMR study on structure, composition and curing behavior of phenol-urea-formaldehyde resole resins

Phenol-urea-formaldehyde (PUF) resole resins were synthesized and analyzed by both liquid and solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy. The liquid ¹³C NMR analysis indicated that the co-condensation reactions between the phenolic ring and the urea unit occurred during the synthesis of the resins. The addition of the urea component effectively reduced the free formaldehyde content in the resin systems. Methylene ether bridges in the resins were found to be mainly associated with the urea units. pH had significant influences on the structure and composition of the resins. Solid-state ¹³C NMR measurements of the cured resins suggested that the pH probably affected the curing mechanism. A longer time and a higher temperature can generally accelerate the curing process and increase the rigidity of the cured network.     

Phenolic resins: 100 Years and still going strong

After 100 years phenolic resins continue to be a prominent resin system with an impressive worldwide volume of nearly 6 million tons/year. It is a ubiquitous adhesive for a diverse spectrum of materials such as wood, glass, metal, paper and rubber with several of these applications being developed by Baekeland during the early stages of his resin commercialization. Many recent technical conferences have been held and were identified with important early Baekeland advances such as Baekeland 2007, Baekeland 2009 and the more recent Baekeland 2011 – all commemorating different initial activities of Baekeland and centennial recognition of his 1907 patent, first production of phenolic resin in Erkner, Germany in 1909 and the centennial celebration of the production of phenolic resin in Japan in 1911. This presentation provides an overview and evaluation of large volume application markets for resole and novolak resins in 2011 and comments related to anticipated greater growth of novolak resins over resole resins. Both resole and novolak resins are viewed as reactive intermediates that undergo a variety of chemical transformations into various improved and in many instances upgraded resin systems that lead to both recognizable and newly reactive resins for value added products. New areas involving phenolic resins are described and consist of Phenol Resorcinol Formaldehyde (PRF) resins, Nanomodification, Novel Novolak Process, ionic liquids, Phenolic Hybrids, and Poly Aryl Ether Amide based on novolak and phenylene bisoxazoline (PBO).     

Structural analysis of phenolic resole resins

The chemical structure and cure characteristics of a group of phenolic resole resins were studied by means of three major analytical techniques. In particular, the effects on structure and reactivity of formaldehyde/phenol ratio and the type of reaction catalyst used were studied. Gel permeation chromatography was used to determine resin molecular weight distributions, and NMR, to determine chemical structural features. In this connection a selective oxidation procedure, converting free methylol groups to adehydes, has allowed unambiguous determination of methylene ether bridge structures to be made from the NMR data. The F/P ratio in a resole largely determines the type of molecular structures which are formed. However, triethylamine as a catalysts tends to favor methylene ether bridge formation, whereas sodium hydroxide favors methylene bridges. The rate and direction of subsequent thermal cure of the resoles prepared is shown by differential scanning calorimetry to depend markedly on the type of catalyst present during the curing stage. The DSC curing curves are interpreted in the light of the structural information provided by NMR.     

Nonisothermal curing of a solid resole phenolic resin

A commercial solid resole phenolic resin was thoroughly characterized with Fourier transform infrared spectroscopy, NMR, and gel permeation chromatography, and its nonisothermal curing reaction was studied systematically with differential scanning calorimetry at a series of heating rates (βs) of 3, 4.5, 5.7, and 10°C/min. The results show that the solid resole had a higher molecular weight than conventional liquid resoles, and its reactive hydroxymethyl (CH₂ OH) and dibenzyl ether (CH₂ O CH₂) functionalities participated in the crosslinking reaction upon heating. The nonisothermal curing reaction of the solid resole exhibited a relatively constant reaction heat, whereas the onset, peak, and end curing temperatures increased gradually with increasing βs. In addition, the reaction kinetics of the solid resole was analyzed with an nth‐order reaction model, the global activation energy was determined with the Kissinger method, and the reaction order was derived from the Crane equation. The obtained rate equation was applied to simulate the reaction time, conversion, and reaction rate, with a good fit achieved between the experimental data and the model predications. In conclusion, this study provided us with new knowledge on solid resoles at a molecular level and was also a great help for the curing procedure design, property optimization, and practical application of this commercial solid resole. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

催化剂对Resole酚醛树脂结构与性能的影响

分别以氨水、三乙胺、氢氧化钠为催化剂合成了3种Resole酚醛树脂,通过pH值,凝胶色谱、红外光谱分析等方法,讨论了不同催化剂的催化反应机理,催化剂对Resole树脂的分子质量及分布以及树脂结构的影响。将3种树脂通过浸渍和热压工艺制备了酚醛树脂层压板,测试了其弯曲性能。结果表明,3种催化剂的催化效率依次为是NaOH>三乙胺>氨水。采用3种催化剂所合成的树脂具有相似的化学结构。采用三乙胺为催化剂时,所制备的层压板具有最佳的工艺性和力学性能。     

Polyaniline Hydrochloride for a Novel Application: Accelerator and Filler for Phenol-Formaldehyde Resin

Abstract

In this work, a study has been made of a novel application of polyaniline hydrochloride (PAn.HCl) in the field of adhesives. Different concentrations of PAn.HCl (0%, 3%, 8%, 13%, 15%, 25%, 35%, 45% and 55% w/w) were blended with phenol formaldehyde resin (resole) by mechanical mixing and the effect of the blending on the adhesive strength and gel time of resin solution was studied. It was discovered that PAn.HCl had an accelerating effect upon the curing of the resin and the curing time was found to be significantly reduced. It was also discovered that PAn.HCl can play a role as a filler in phenolic resin polymer matrices, resulting in an improvement in the mechanical properties (adhesive strength) of the prepared resins. Resole and its blends with PAn.HCl were characterized in terms of their structure, by Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The room temperature d.c. electrical conductivities of resole and resole/PAn.HCl blends were studied by the conventional four-point probe method.     

Sustainable phenolic thermosets coatings derived from urushiol

The over-exploitation of finite fossil resources and/or the increased environmental and sustainable awareness inspire scientists and technologists to search for inexpensive alternatives from renewable chemicals. Phenol formaldehyde (PF) resins, the oldest type of synthetic polymers with good mechanical properties and heat resistance, are widely used in the production of coatings, laminates, molding compositions, and glues. Here, biobased urushiol-derived PF resins were synthesized from the alkali-catalyzed reaction between urushiol and formaldehyde. The chemical compositions and molecular structures of resole resins were characterized by carbon-13 nuclear magnetic resonance and Fourier transform infrared spectroscopy, and their curing behaviors were studied by differential scanning calorimetry. The as-prepared urushiol-derived resole resins had methylol (Ph−CH₂OH), ortho- and para-hemiformal groups (Ph−CH₂OCH₂OH), and the para−para/ortho−para/ortho−ortho links of methylene groups (Ph−CH₂−Ph), whereas the resole resins had low curing temperatures at about 100–113°C. Additionally, given the long side alkyl group moiety on the aromatic rings of urushiol, the films of cured urushiol-derived resole resins had low glass transition temperatures of 132 ± 2°C. Furthermore, the as-prepared urushiol-derived coatings exhibited excellent physical and mechanical properties.     

Condensation–addition‐type resole resins with phenyl ethynyl functions: Synthesis,characterization, and thermal properties

Novel phenolic resins bearing methylol and phenyl ethynyl functions and curing by both condensation and addition mechanisms were synthesized by the reaction of 3‐(phenyl ethynyl) phenol (PEP) with formaldehyde under alkaline conditions. Resins with varying relative concentration of the two functional groups were synthesized and characterized. The resins underwent a two‐stage cure, confirmed by both DSC and DMA analyses. The low‐temperature cure due to methylol condensation led to early gelation of the system. The ultimate curing through addition reaction of phenylethynyl group required heating at 275°C. The cured resins exhibited better thermal stability and anaerobic char yield in comparison to a conventional resole. The thermal stability and char‐yielding property showed a diminishing trend with enhanced methylol substitution. Resin with F/P ratio less than unity offered excellent thermal stability and anaerobic char yield. The thermal degradation of the cured resins occurred in two kinetic steps. Methylene groups favored the initial degradation, whereas the higher temperature carbonization process was independent of the network structure. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3371–3377, 2001     

Computer-simulation der polykondensation von phenol mit formaldehyd

The polycondensation of phenol with formaldehyde to resole type phenolic resins has been studied using a kinetic model suitable for computer simulation. Important properties like residual amounts of monomers, number average degree of polymerization as well as degrees of branching and methylolation are calculated as functions of time for different values of initial molar ratios of phenol to formaldehyde and various rate constants. In addition the influence of intramolecular curing, due to formation of loops has been discussed in detail.     

Dynamic mechanical analysis study of the curing of phenol‐formaldehyde novolac resins

The curing reaction of typical commercial phenol‐formaldehyde novolac resins with hexamethylentetraamine (HMTA) was followed by dynamic mechanical analysis. The evolution of the rheological parameters, such as storage modulus G′, loss modulus G″, and tanδ (G″/G′), as a function of time, for samples of the phenolic resins on cloth, was recorded. The curing reaction, leading to the formation of a crosslinked structure, is described by a third‐order phenomenological equation. This equation takes into account a self‐acceleration effect, as a consequence not only of the chemical reaction of crosslinking after the gel point but of phase segregation as well. This rheokinetic model of the curing of phenolic novolac resins permits the determination of the numerical values of the kinetic equation constants. The influence of the composition, structure, and physical treatment on the curing kinetics of the novolac resins is evaluated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1902–1913, 2001     

Adhesives and coatings based on poly(vinyl acetal)s

Phenolic resins such as resole phenol– and cresol–formaldehyde, as well as low-molecular-weight epoxy resin based on bis(4-hydroxy phenol) cyclohexane were prepared and modified with various types of the prepared poly(vinyl acetal)s. Poly(vinyl formal), poly(vinyl isobutyral), and poly(vinyl propional) were used. This study indicated that the optimum conditions for curing phenolic or epoxy resin–poly(vinyl acetal)s adhesive compositions are of an equal weight ratio or a 2 : 1 weight ratio in the presence of phthalic anhydride (10 or 20 wt %) of resin content as a curing agent at 150°C for 20 or 60 min, respectively. The effect of acetal type on the tensile shear strength values of resin samples, cured under the previously mentioned optimum conditions for different times, was investigated. The effect of structure of cresol–formaldehyde and epoxy resins was also studied. Metallic and glass coatings from the previous pure resins and their formulated mixtures were also prepared and evaluated as varnishes or paints. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1769–1777, 1998     

Epoxy resins toughened by poly(propylene carbonate)

Poly(propylene carbonate) (PPC) was used as a toughening agent for improving the brittleness of cured epoxy resins (EP). Methyl tetrahydrophthatic anhydride (MTHPA) was used as a curing agent. The activation energies for the reactions of PPC/MTHPA and EP/MTHPA measured by FTIR were 115.8 and 66.5 kJ/mol, respectively, while for the composite system of PPC/EP/MTHPA, the activation energy obtained from DSC was 52.9 kJ/mol. Gel contents, DMA, and DSC displayed that the cured resins of PPC/EP/MTHPA were phase-separation crosslinking systems and most of PPC could react with MTHPA or the epoxy group. The toughness of cured resins was reinforced by the addition of PPC. The optimum mechanical properties and toughness for cured resins of PPC/EP/MTHPA corresponded to the system containing 20 phr PPC, which achieved a 33% increase in tensile strength and a 45% increase in the fracture toughness at no expense of the elongation of cured resins. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 2457–2465, 1997     

Graphitization of phenolic resins for carbon-based refractories

The chemical resistance and thermo-mechanical properties of refractories bonded with resole or novolak resins depend on the presence of crystalline carbon phases (preferentially with features close to graphite ones) in their compositions. Although thermosetting resins are commonly classified as non-graphitizing carbon sources, many efforts have been made in recent years in order to find effective routes to induce the in situ graphitization of such components in refractory products during service. This work evaluates the role of processing parameters (mixing, curing and firing temperature) and additives (ferrocene, boric acid and exfoliated graphite) in the graphitization process of two commercial resins (resole and novolak) and a synthesized one (modified-novolak). X-ray diffraction, Raman spectroscopy and thermogravimetric analyses were carried out to identify the microstructural evolution of the compositions. According to the results, carbon graphitization was already detected after firing the samples at 1000 °C for 5 h under reducing atmosphere. Ferrocene addition favored a more effective graphitization of the selected resins, but H₃BO₃ also induced the rearrangement of the carbon derived from the commercial novolak product. The mixing and curing procedures used when preparing the compositions proved to be very important steps as they affected, to a greater extent, the resulting graphitization degree of the fired samples.     

酚醛树脂固化动力学研究及其耐热性能评价

利用差示扫描量热(DSC)法分析了甲醛、苯酚物质的量之比为1.9:1、1.7:1、1.5:1、1.3:1时酚醛树脂(PF)的固化性能,采用Kissinger法计算了4批PF固化反应的表观活化能。用热失重分析(TG)法对4批PF的耐热性能进行了考察。试验结果表明,甲醛、苯酚物质的量之比为1.7:1时,PF的固化反应活化能最低,即固化时需要较少的热量,易固化,其耐热性能最好。     

Novel phosphorilated flame retardant thermosets: epoxy-benzoxazine-novolac systems

Modified novolac resins with benzoxazine rings were prepared and cured with isobutyl bis(glycidylpropylether) phosphine oxide (IHPOGly) as crosslinking agent. Their curing behaviour using different epoxy/phenol molar ratios and with or without triphenylphosphine as catalyst was studied. Two different phenolic groups react with oxirane ring, those initially free and those generated after benzoxazine ring opening. In absence of catalyst, it is not possible to distinguish between them. However, for the catalyzed curing of the highest modification degree benzoxazine based novolac resin is possible to distinguish both reactions. The thermal, thermomechanical and flame retardant properties of the cured materials were measured. V-O materials were obtained when the resins were tested for ignition resistance with the UL-94 test.