Phenol-formaldehyde Prepolymer Research Articles

Assessment of phenol-formaldehyde adhesive distribution on the strand surface by light microscopy

This study reports on a new approach for the detection of phenol-formaldehyde (PF) resin distribution on the strands surface after air-spray application in a glue drum using reflecting light microscopy (LM). The method allows visualization and quantification of PF adhesive distribution on wood strands by using either waterproof paper or 200 µm thick microtomed kiri (Paulownia tomentosa) veneer slices, which were clipped with staples on conventional strands typically used for the production of oriented strand boards (OSB). These strands were mixed with other conventional OSB strands and two types of molecular weight PF prepolymers were sprayed on the strand mixture. While the total area of adhesive coverage was similar for both adhesives, the low molecular weight (LMW) PF prepolymer formed a higher number of adhesive droplets than the high molecular weight (HMW) PF prepolymer. The study offers a new, easy applicable approach for a qualitative investigation of adhesive distribution on the strand surface during gluing on a laboratory and pilot plant scale.

Birch Wood Surface Characterization after Treatment with Modified Phenol-Formaldehyde Oligomers.

Phenol-formaldehyde (PF) resins with well-established molecular sizes are promising treatment agents for wood bulk protection. However, due to the presence of hydroxyl groups on the periphery, the PF oligomers tend to absorb the water, which can lead to water penetration into the wood. To overcome this drawback different PF pre-polymers have been chemically modified with different long-chain fatty acid chlorides (FAC) via esterification. To obtain the modified PF (M-PF) resins, the PF pre-polymers with average molecular weight (Mw) from 266 to 884 g/mol were esterified with decanoyl, lauroyl, myristoyl, palmitoyl, and stearoyl chloride in pyridine as the reaction medium. Silver birch (Betula pendula) wood specimens (15 × 70 × 150 mm3) were coated with M-PF pre-polymer 5% (w/w) solutions in tetrahydrofuran (THF), and hydrophobic properties of treated birch wood specimens were evaluated using surface contact angle (CA) measurements of water droplets. For all M-PF resin-treated specimens, CA was almost 2–2.5 times higher than for untreated wood (45°) and it remained 80–125° after 60 s. The aging properties of M-PF resin-coated birch wood were analyzed using artificial weathering with ultraviolet (UV) light and combination of both UV and water spray. Results clearly confirm, that the hydrophobic properties of M-PF-treated wood has short-term character and will gradually disappear during long-term application in outdoor conditions.

The evolution of nanopores in allylated calixarene resin during thermal cure

In this paper one kind of new thermosetting resin, allyl etherified calixarene (allylated calixarene), was prepared and investigated. Claisen rearrangement reaction could not occurred due to the existence of para-positioned substituent in allylated calixarenes, and thermal cure proceeded at comparably low curing temperature (210–230 °C, lower than the curing temperature of allylated Bisphenol-A and allylated phenol-formaldehyde prepolymer at 330 °C). Allylated p-methylcalixarene cannot remain its nanopore conformation (i.e., cone conformation) even before its thermal cure. Allylated p-tert-butylcalixarene can keep its cone conformation at room temperature and low curing temperature (e.g., <130 °C), however its nanopores will be destroyed upon heating at high temperature (the gradually level-off and quietly weak diffraction peak in the Small Angle X-ray Diffraction profile). Allylated p-phenylcalixarene can preserve its nanopore conformation at room temperature and high curing temperature (e.g., 200 °C). The results indicated that the larger para-substituent will hinder the inversion of phenolic ring, and the higher curing temperature will promote the rotation of phenolic ring.

Adhesive and curing properties of chicken feather/blood-based adhesives for the fabrication of medium-density fiberboards

ABSTRACTThis study was conducted to investigate the adhesive properties of chicken feather (CF)-based adhesives for wood-based panels. CF was hydrolysed in sodium hydroxide solutions of 5%, 7.5% and 10% (CF-AK). Chicken blood (CB) hydrolysed in sulfuric acid solution of 5% (CB-AC) was used as a hardener. The adhesives were formulated by crosslinking 60% CF-AK, 10% CB-AC and 30% formaldehyde-based crosslinking agents (formalin, melamine-urea-formaldehyde and phenol-formaldehyde prepolymers) on a solid weight basis. The CF-based adhesives were very viscous at room temperature, but the viscosity at 50 °C ranged from 300 to 600 mPa·s resulting in a sprayable adhesive. From the DSC analysis, the use of CF-AK-10% in the CF-based adhesives need longer curing time compared with that of CF-AK-5%. Most mechanical strength properties and dimensional stability of MDF bonded with CF-based adhesives were similar to those of commercial urea-formaldehyde (UF) resin. However, internal bonding strength of most MDF bonded with CF-based adhesives was higher than that with the UF resin. Most adhesive properties of the MDF manufactured with the new CF adhesive met the Korean Standard requirements for interior MDF. These results suggest that CF and/or CB can be used as raw materials for environment-friendly adhesives for producing wood panels.

Adhesive Properties of Medium-Density Fiberboards Fabricated with Rapeseed Flour-Based Adhesive Resins

This study examined the adhesive properties of adhesives formulated with rapeseed flour (RSF), a by-product of edible oil and bio-diesel manufacture, for medium-density fiberboards (MDFs). The RSF was hydrolyzed by sulfuric acid (AC-RSFH) and sodium hydroxide (AK-RSFH) solutions of 3%, 5%, and 7%. Phenol–formaldehyde (PF) prepolymers were prepared with formaldehyde to phenol molar ratios of 1.5, 1.8, and 2.1 (1.5-, 1.8-, and 2.1-PF). RSF-based adhesives were formulated by cross-linking 35% AC-RSFH, 35% AK-RSFH, and 30% PF prepolymers on a solid weight basis. The mechanical strength and dimensional stability of the MDFs were improved by decreasing the concentration of RSF-hydrolytic agents. The properties of the MDFs bonded with RSFH/1.8-PF resins were superior to those of RSFH/1.5- or 2.1-PF resins. These results suggest that RSF can be used as a raw material for environment-friendly adhesives used in MDF production.

유채박 가수분해물을 이용한 중밀도섬유판(MDF) 제조용 접착제의 개발

목질 판상재료 생산을 위하여 현재 주로 사용되고 있는 석유화학계 접착제를 대체하여 재생가능한 원료로부터 대체 접착제를 개발하기 위한 관심이 증대하고 있다. 본 연구에서는 바이오 디젤 부산물인 유채박을 산 및 알칼리 가수분해를 통해 접착제를 제조하고, 이 접착제를 중밀도섬유판(MDF) 제조에 적용한 후 물성과 강도 특성을 조사하여 유채박의 중밀도 섬유판 제조용 접착제에 대한 가능성을 확인하고자 하였다. 먼저 유채박 접착제 조제를 위하여 유채박을 산과 알칼리 가수분해를 통해 개량한 다음, phenol formaldehyde (PF) prepolymer 와 혼합하여 접착제를 제조하고 이를 중밀도 섬유판 제조용 접착제로 사용하였다. 제조된 중밀도 섬유판의 평균 함수율과 밀도는 모두 KS의 기준을 만족시키는 것으로 나타났으며, 흡수 두께 팽창률은 다소 높게 나타났다. 중밀도 섬유판의 휨강도는 요소수지 접착제로 제조한 중밀도 섬유판보다 낮은 것으로 나타났지만 박리강도는 일부 조건에서 요소수지 접착제로 제조한 중밀도 섬유판보다 높게 나타나 석유화학계 접착제의 대체 접착제로의 가능성을 보여주었다. 접착성능의 향상을 위해서는 최적화되는 중밀도 섬유판의 제조공정의 변수에 대한 추가 연구가 필요할 것으로 생각된다. The interest to develop adhesives from renewable resources is growing to substitute petroleum-based adhesive resins in the manufacture of wood based panels. In our study, rapeseed flour (RSF), which is the by-product of bio-diesel produced from rapeseed, were hydrolyzed with acid and alkali. As a crosslinking agents of the RSF hydrolyzates, phenol-formaldehyde prepolymers (PF) were prepared. The RSF hydrolyzates and PF were mixed to complete the formulation of RSF-based adhesive resins, and the resins were applied to make the medium density fiberboard (MDF). The physical and mechanical properties of the MDF were measured to examine whether RSF can be used as raw materials of adhesive resins for the manufacture of MDF or not. The average moisture content and density of the MDF made with RSF-based adhesive resins satisfied the minimum requirement of KS standard, but the thickness swelling was not. The bending strengths of the MDF made with RSF-based adhesive resins were lower than that of the MDF made with commercial UF resins, but the internal bonding strengths of tested MDF in some make-up conditions of RSF-based adhesive resins were higher than that of MDF made with commercial UF resins. These results showed the potential of RSF as a raw material of adhesives for the production of MDF. Future works on the optimal manufacturing process conditions of MDF made with RSF-based adhesive resins are required to improve the performance of MDF made with RSF-based resins.

유채박을 이용한 단판적층재용 접착제의 개발 및 성능평가

목질계 판상재료 생산을 위하여 현재 주로 사용되고 있는 석유화학계 접착제는 원유의 가격 상승과 포름알데히드 방산과 같은 문제로 인해 대체 접착제에 대한 개발 필요성이 오래전부터 대두되었다. 본 연구에서는 석유화학계 접착제를 대체하기 위하여 바이오 디젤 부산물인 유채박의 효소 가수분해를 통해 접착제를 조제하고, 이 접착제를 단판적층재 제조에 적용한 후 물리 및 기계적 특성을 조사하여 유채박의 단판적층재 제조용 접착제 제조를 위한 원료화 가능성을 확인하고자 수행하였다. 먼저 유채박 접착제 조제를 위하여 유채박을 4가지 효소의 조합을 통해 개량한 다음, phenol formaldehyde (PF) prepolymer와 혼합하여 접착제를 제조하고 이를 단판적층재 제조에 사용하였다. 제조된 단판적층재의 평균함수율과 내수성은 모두 KS의 기준을 만족시키는 것으로 나타났으며, 유채박 접착제의 열분석에서 pectinase 가수분해물로 조제한 접착제를 제외하고 페놀수지 접착제와 열경화 특성이 큰 차이를 보이지 않았다. 단판적층재의 휨강도는 페놀수지 접착제로 제조한 단판적층재보다 높거나 유사한 것으로 나타나 기존 석유화학계 접착제의 대체 접착제로써 가능성을 보여주었다. 추후 접착성능의 향상을 위해 적절한 유채박의 효소가수분해 조건에 대한 연구와 도포성능 개선에 대한 연구가 필요할 것으로 생각된다. Due to the increase of oil price and the environmental issue such as the emission of volatile organic compounds, the necessity for developing alternative resins of petroleum-based adhesive resins, which have extensively been used for the manufacture of wood-based products, has been speculation since the early 1990. In our study, rapeseed flour (RSF), which is the by-product of bio-diesel produced from rapeseed, were hydrolyzed by enzymes. As a crosslinking agents of the RSF hydrolyzates, phenol-formaldehyde prepolymers (PF) were prepared. The RSF hydrolyzates and PF were mixed to complete the formulation of RSF-based adhesive resins, and the resins were applied to make the laminated veneer lumber (LVL). The physical and mechanical properties of the LVL were measured to examine whether RSF can be used as raw materials of adhesive resins for the fabrication of LVL or not. The average moisture content and soaking delamination rate of the LVL bonded with RSF-based adhesive resins exceeded the minimum requirement of KS standard. Moreover, thermal analysis of the RSF-based resins showed similar tendencies except for the RSF-based adhesive resins formulated with pectinase-hydrolyzed RSF. The bending strengths of the LVL were higher than that of the LVL made with commercial PF resins. These results showed the potential of RSF as a raw material of alternative adhesives for the production of LVL. Further works on the optimal conditions of RSF hydrolysis and spreading characteristics for RSF-based adhesive resins is required to improve the adhesive performance of RSF-based resins.

유채박의 알칼리 가수분해물을 이용한 합판용 접착제의 개발

현재 석유화학계 접착제는 합판과 같은 목질계 판상재료 생산을 위하여 주로 사용되고 있다. 그러나 석유화학계 접착제의 기본 원료인 원유의 가격 상승과 포름알데히드 방산과 같은 문제로 대체 접착제에 대한 개발이 절실한 상황이다. 본 연구는 석유화학계 접착제를 대체하기 위하여 바이오 디젤 부산물인 유채박을 이용하여 접착제를 조제하였으며, 이 접착제를 합판 제조에 적용한 후 접착능 및 포름알데히드 방산량을 조사함으로써 유채박의 합판용 접착제 제조를 위한 원료화 가능성을 확인하고자 하였다. 유채박 접착제 조제를 위하여 먼저 유채박을 수산화나트륨으로 화학적으로 개량한 후, phenol formaldehyde (PF) prepolymer와 혼합하여 접착제를 제조하고 그 접착제를 합판 제조에 적용하였다. 유채박 접착제는 가수분해 조건과 PF prepolymer의 몰비에 따라 26.08~36.12%의 고형분 함량을 보유하였으나, 점도가 매우 높은 것으로 조사되었다. 한편 유채박 접착제로 제조된 합판의 인장 전단강도와 목파율은 유채박의 가수분해 조건과 PF prepolymer의 종류와 상관없이 KS 규격의 보통 합판 품질기준을 상회하였다. 포름알데히드 방산량은 1.8몰의 포름알데히드와 1몰의 phenol로 조제한 PF prepolymer를 사용한 접착제에서 유채박의 가수분해 조건과 상관없이 KS 규격의 E0 기준보다 낮은 것으로 나타났다. 결과적으로 유채박이 합판용 접착제의 원료로서 사용될 수 있을 것으로 생각되나, 열압시간을 단축시키기 위한 유채박 접착제의 고형분 함량을 증가시키는 방안과 접착제의 목재 침투 정도와 인장 전단강도 사이의 관계를 확인하는 현미경적 미세구조에 대한 연구가 유채박 접착제의 상용화를 위해 필요할 것으로 판단된다. Petroleum-based adhesive resins have extensively been used for the production of wood panels. However, it is necessary to develop environmentally friendly adhesive resins due to the increase of manufacturing cost and the environmental issue, such as the emission of volatile organic compounds, of the pertroleum-based adhesive resins. This study was conducted to formulate environmentally friendly adhesive resins using by rapeseed flour (RSF), which is the by-product of bio-diesel produced from rapeseed, for replacing petroleum-based adhesives with them. To formulate RSF-based adhesive resins, RSF was hydrolyzed in de-ionized water, 1% and 3% sodium hydroxide solutions. As a crosslinking agent, PF prepolymers were prepared with 1.8, 2.1 and 2.4 mol formaldehyde and 1 mol phenol (1.8-, 2.1- and 2.4-PF), and then mixed with RSF hydrolyzates to complete the formulation of RSF-based adhesive resins. The RSF-based adhesive resins were applied to fabricate 3-ply plywood panels. The solid content of RSF-based adhesive resins were ranged from 26.08% to 36.12% depending on the hydrolysis condition of RSF and PF prepolymer type with a high viscosity. The tensile shear strength and wood failure of plywood fabricated with RSF-based adhesive resins exceeded a minimum requirement of KS standard for ordinary plywood regardless of the hydrolysis condition of RSF and PF prepolymer type. Formaldehyde emissions of the plywood panels fabricated with 1.8-PF and RSF hydrolyzates were lower than that of E0 specified in the KS standard. Based on the results, RSF might be used as a raw material of environmentally friendly adhesives for the production of plywood panels, but further researches - the increase of solid content of RSF-based adhesives for reducing press time and the microscopic observation of plywood specimen for identifying the relationship between tensile shear strength and the penetration of adhesives into wood structure - are required to commercialize the RSF-based adhesives.

Structure and curing mechanism of resol phenol-formaldehyde prepolymer resins

Prepolymer resol resins with different phenol/formaldehyde/NaOH molar ratios were synthesized and characterized by technical analysis as well as by 13 C NMR spectra for samples in CD3OD solution. Larger amounts of NaOH promoted the binding of formaldehyde and para substitution including the formation of benzoquinone rings with two o, p'-methylene groups in the para position. The polycondensation between ortho-hydroxymethyl groups and one-substituted aromatic para positions as the main thermosetting curing process continued in the heat treatment of resol resins. The self-condensation between ortho-hydroxymethyl groups, the release and oxidation of formaldehyde, and the formation of hemiformals are processes of low significance in curing resol resins. The assignment of 13 C NMR resonances depending on the presence of phenolic hydroxyl groups, phenoxide ions, and substituted quinone rings is discussed.

Morphology Control of Carbon, Silica, and Carbon/Silica Nanocomposites: From 3D Ordered Macro-/Mesoporous Monoliths to Shaped Mesoporous Particles

We demonstrate that confinement of a concentrated triconstituent precursor solution (a soluble phenol-formaldehyde prepolymer, tetraethylorthosilicate, and the nonionic triblock copolymer F127) in a poly(methyl methacrylate) (PMMA) colloidal crystal template permits control over the external morphology of mesostructured products. It is possible to produce either monoliths with hierarchical porosity (ordered macropores from PMMA spheres and large mesopores from F127) or cubic and spherical mesoporous nanoparticles. The specific morphology depends on the concentration of F127 and on the presence of 1,3,5-trimethyl benzene (TMB) as an additive. At lower F127 content and without TMB, macroporous monoliths of the carbon/silica composite are obtained, which can be converted to carbon monoliths with dual porosity after the extraction of silica with hydrofluoric acid or to silica monoliths after calcination in air. Large worm-like mesopores are present in macropore walls. An increase in the F127 concentration lea...

Kinetics of hydroxymethyl phenols formation by in‐line FTIR spectroscopy

AbstractThe kinetics of phenol–formaldehyde prepolymers catalyzed by sodium hydroxide at various temperatures was studied. Several reactions were conducted with different phenol to formaldehyde as well as phenol to sodium hydroxide molar ratios. The React‐IR system was used to monitor the reaction as well as to determine residual free phenol and formaldehyde.The changes in the concentrations of phenol and formaldehyde with the reaction time were determined. The value of the concentration of the hydroxide ion, [OH−], was obtained by measuring the pH value of reaction mixture. The concentration of the hydroxide ion, [OH−], expressed as a function of reaction time, was fitted by the six‐order polynomial to the experimental data. On the basis of the proposed reaction scheme the kinetic model was developed. The kinetic parameters were obtained by adjusting the experimental evolution of phenol and formaldehyde during the synthesis. Using this method the changes in the concentrations of five species of hydroxymethyl phenols with the reaction time was also been calculated. The activation energy and preexponential factor have been calculated for individual reactions. The accuracy of the kinetic model was confirmed by comparing experimental concentration profiles of formaldehyde and phenol with the calculated ones for different molar ratios. The experimental tendencies are in agreement with the results of the model. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Fully quantitative carbon-13 NMR characterization of resol phenol–formaldehyde prepolymer resins

Different resol phenol–formaldehyde prepolymer resins have been synthesized with different Formaldehyde/Phenol (F/P) ratios or different catalysts and characterized by 13C NMR spectroscopy in solution. A fast quantitative measuring protocol is proposed based on the use of chromium(III)acetylacetonate as a relaxation agent. APT (attached proton test) and DEPT (distortionless enhancement by polarisation transfer) spectra were acquired to enable proper resonance assignments, especially in the regions with severe signal overlap. Equations are presented in which the methylene bridges (MB), the methylol groups (MG) and the dimethylene ether bridges (DMEB) of resol resins are quantitatively taken into account. Important structural factors determined quantitatively for resol prepolymer resins are the F/P ratio after reaction, the degree of polymerization ( n), the number average molecular weight ( M n) and the content of free ortho and para positions.

One‐ and two‐dimensional NMR study of resol phenol—formaldehyde prepolymer resins

AbstractA one‐ and two‐dimensional NMR study was performed on three commercial resol phenol—formaldehyde (PF) prepolymer resins. 1H, 13C, CSCM and DQF COSY NMR spectral data, in acetone‐d6, were obtained on each resin and on PF model compounds: phenol, five methylolphenols, four diphenylmethanes, two formals, two dibenzyl ethers and two dibenzylamines. Gated‐decoupled 13C experiments, using 2,4,6‐trimethylphenol as internal standard, were used to quantitate the major components present in each of the three resins. The major chemical differences of the three resins were noted. A DQF COSY method was developed that allowed the qualitative identification of most of the major phenolic components present in each of the PF resins.

Quantitative Analysis of Gross Adhesive Penetration in Wood Using Fluorescence Microscopy

Abstract An optimum amount of adhesive penetration is desirable for economy of production and development of bond strength in wood composites. A general method that allows quantitative measurement of gross adhesive penetration in wood is described. Staining techniques have been developed that can provide sharp contrast between a cured adhesive and the wood substrate using fluorescence microscopy. An image analysis system utilizes this contrast to quantify gross adhesive penetration in wood. An example of this technique is provided, whereby the effect of molecular weight distribution of phenol formaldehyde prepolymers on gross adhesive penetration into yellow poplar (Liriodendron tulipifera) flakes is observed and quantified. Adhesive penetration into wood flakes was shown to be correlated with the molecular weight distribution of the prepolymer, decreasing with higher weight average molecular weight. Gross adhesive penetration into hardwoods is likely to be dominated by flow into vessel elements, as demon...

1H- and13C-NMR Studies on Phenol-Formaldehyde Prepolymers for Tannin-Based Adhesives

Abstract The number average structure and the molecular weight distribution of phenol-formaldehyde prepolymers for use in synthesis of tannin-based adhesive resins were determined with 1H- and 13C-NMR spectroscopy and gel permeation chromatography of acetylated resins. These methods were used to determine differences in phenol-formaldehyde prepolymens prepared under different reaction conditions. Quantitative 13C-NMR techniques provided a detailed analysis of the structure of a phenol-formaldehyde prepolymer.