• Korean Journal of Materials Research
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• v.26 no.9
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• pp.472-477
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• 2016

Microstructure evolutions of thermosetting resin coating layers fabricated by electrostatic spray deposition (ESD) at various processing conditions were investigated. Two different typical polymer systems, a thermosetting phenol-formaldehyde resin and a thermoplastic polyvinylpyrrolidone (PVP), were employed for a comparative study. Precursor solutions of the phenol-formaldehyde resin and of the PVP were electro-sprayed on heated silicon substrates. Fundamental differences in the thermomechanical properties of the polymers resulted in distinct ways of microstructure evolution of the electro-sprayed polymer films. For the thermosetting polymer, phenol-formaldehyde resin, vertically aligned micro-rod structures developed when it was deposited by ESD under controlled processing conditions. Through extensive microstructure and thermal analyses, it was found that the vertically aligned micro-rod structures of phenol-formaldehyde resin were formed as a result of the rheological behavior of the thermosetting phenol-formaldehyde resin and the preferential landing phenomenon of the ESD method.

• Journal of the Korean Wood Science and Technology
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• v.21 no.1
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• pp.51-58
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• 1993

The phenol resorcinol formaldehyde resin (PRF) adhesives which are curing at ambient temperature for structural purposes were synthesized. A PRF resin is produced according to the two-stage reaction system. In first stage, a low-condensed resol or methylolated phenol were prepared from phenol by reaction with a formaldehyde in alkaline condition. The molar ratio of phenol to formaldehyde was 1.0~1.4. And in second-stage, resorcinol was added to combine with the methylol group of a low-condensed resol(R/P molar ratio 0.3). The glue-joint strength, pot-life and workability of this synthetic PRF resin were superior to conventional ambient temperature setting adhesives such as oilic urethane or water based polymer-isocyanate resin for wood adhesives.

• Journal of the Korean Wood Science and Technology
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• v.15 no.1
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• pp.1-11
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• 1987

A kraft black liquor obtained from pulping of pine (Pinus densiflora Sieb et Zucc) was used for producing three kinds of adhesive such as black liquor-phenol formaldehyde resin, methyloeated kraft lignin-phenol formaldehyde resin, and lignin cake-phenol resin. In case of producing black liquor-phenol formaldehyde resin, about 60 percent of the phenolic resin could be replaced by black liquor. Also the optimal press condition appeared to be $160^{\circ}C$ for 7 min. (l5.77Kg/$cm^2$ in dry test, 8.54Kg/$cm^2$ in 4 hr. boil test). Phenol could be substituted up to 80-90 percent by methylolated kraft lignin. The suitable conditions of factors affecting bond quality were pH to 2.6, methanol as solvent and 0.2ml formaldehyde per 1g of the adhesives, respectively. The optimal press condition was $150^{\circ}C$ for 4 min. (188.54Kg/$cm^2$ in dry test, 10.08Kg/$cm^2$ in 4 hr. boil test). In preparing lignin cake-phenol resin, a suitable mixing ratio of phenol to powered kraft lignin was one to one by weight. The optimal press condition was $150^{\circ}C$ for 4 min.(18.46Kg/$cm^2$ in dry test, 12.31Kg/$cm^2$ in 4 hr. hoil test).

• Journal of the Korean Wood Science and Technology
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• v.23 no.3
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• pp.33-39
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• 1995

To accelerate the cure of phenolic resin adhesives for plywood, the complexation with melamine resin and the addition of cure-accelerating agents were discussed. The hot-pressing temperature and time of phenol resin could be decreased by complexation with melamine resin. but the wet glue-joints strength of phenol melamine resin was lower than that of ordinary phenol resin in case of plywood using spruce veneer at core layer. Among the tested cure-accelerating agents. the sodium carbonate showed the greatest effect on shortening gelation time of phenolic resin. In addition, in the manufacturing scale test, the hot-pressing time of phenol resin with the addition of 5 parts sodium carbonate could be shortened about 20% compared with ordinary phenol resin which had same glue-joints properties.

• Applied Chemistry for Engineering
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• v.16 no.2
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• pp.288-291
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• 2005

Resol type phenol-formaldehyde (PF) resin was synthesized by addition reaction of formaldehyde (F) and phenol (P). And the PF resin was synthesized by condensation reaction in which water was removed. In this work, we studied the influence of experimental parameters in the addition reaction, such as F/P mole ratio, amount of catalyst, reaction temperature, reaction time, and so on. Also, we studied the influence of molecular weight and viscosity of PE resin as a function of condensation time. As a result, in addition reaction, the reaction time decreased remarkably as the catalyst concentration increased, and the time decreased with increasing reaction temperature at a constant catalyst concentration. Also, in condensation reaction, the viscosity of resol type PF resin increased from 1500 to 9000 cps as a function of condensation time; molecular weight showed from 500 to 1100 g/mol.

• Journal of the Korean Wood Science and Technology
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• v.32 no.3
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• pp.25-32
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• 2004

This research work explored physical and mechanical properties of impregnated sawdust boards from three softwood species (P, densifora, L. kaemferi, and P. koraiensis) with phenol-formaldehyde (PF) resin by various vacuum treatment methods of combining pressure, vacuum, and ultrasonic waves. Simultaneous vacuum and ultrasonic wave treatments with no pressure resulted in the greatest increase in resin content, density, dimensional changes (thickness and length), bending strength, and hardness of impregnated board. This result seemed to be attributed to the ultrasonic wave treatment.

• Journal of the Korean Wood Science and Technology
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• v.24 no.2
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• pp.15-19
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• 1996

To utilize the waste materials and develope wood adhesive from isolated bloods of slaughtered cow and pig and also to prevent water pollution, simple and rapid method of isolation and purification of plasma proteins from pig bloods with trichloroacetic acid(TCA) treatment was developed. Adding of TCA-precipitated blood powder to the phenol formaldehyde resin(PF) improved dry and wet strength of plywood and resulted in fast hot pressing times.

• Journal of Preventive Medicine and Public Health
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• v.27 no.2 s.46
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• pp.274-285
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• 1994

The effects of resin on the respiratory health have been investigated in 309 workers from four iron and steel foundries and the results compared with those from 122 workers who were not significantly exposed to resin gas and silica dust at the same industries. Phenol-formaldehyde resin was used in the core making and molding processes and workers were exposed to their decomposition products as well as to silica dust containing particulates. The subjects were grouped according to formaldehyde, dust and other gas exposures, and smoking habits were considered also in thi analysis. Standardized respiratory symptom questionnaire was administered by trained interviewers. Chest radiograph, pulmonary funtion tests, and methacholine challenge tests were done. Environmental measurements at the breathing zone were carried out to determine levels of formaldehyde, respiable dust and total dust. Foundry workers had a higher prevalence of symptoms of chronic bronchitis with chronic phlegm and chronic cough when exposed to dust. Exposure to gas was significantly associated with lowered $FEV_1$ and obstructive pulmonary function changes. Exposure to formaldehyde and phenol gas was associated with wheezing symptom among workers, but $FEV_1$ changes after methacholine challenge were not significantly different among different exposure groups. When asthma was defined as the presence of bronchial hyperreactivity with more than 20% decrease in $FEV_1$ after methacholine challenge, 17 workers out of 222 tested had asthma. Fewer asthmatic welters were found among groups exposed to formaldehyde, gas and dust, which indicates a healthy worker effects ill a cross-sectional study. The concentration of formaldehyde gas ranged from 0.24 to 0.43 ppm among studied foundries. The authors conclude that formaldehyde and phenol gas from combusted resin is probably the cause of asthmatic symptoms and also a selection force of those with higher bronchial reactivity away from exposures.

• Journal of the Korean Applied Science and Technology
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• v.24 no.4
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• pp.339-346
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• 2007

The influence of adding urea to phenol-formaldehyde (PF) resins as a co-polymer component were investigated aiming at synthesizing useful phenol-urea-formaldehyde resins. Urea was added at 10% by total resin weight. Several methods for the addition of urea to the PF resins during synthesizing resins to see the co-polymerization occurs between urea and PF resins. The urea was added at the beginning, at three different middle stages, and at the end of PF resin synthesis. The copolymerized methylene bridges between phenol and urea molecules were not observed by $^{13}C-NMR;$ no signal around 50ppm. The curing of urea-modified PF resins, evaluated by dynamic mechanical analysis(DMA), showed some differences among the resins. DMA gel times ranged from 2.75 min to 3.25 min and the resins made with earlier urea additions showed slightly shorter gel times. The longest cure time and gelation time was observed for the resin PFU. Catalyst effects on the DMA cure time values of resins were not significant with different amounts of catalyst or different types of catalyst for all resins tested. Gel times of urea-modified PF resins shortened the most by triacetin catalyst.

• Journal of Adhesion and Interface
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• v.7 no.1
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• pp.16-22
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• 2006

In this work, the effect of cure temperature and time on the thermal stability and the exothermic cure reaction peak of a waterborne resol-type phenol-formaldehyde resin, which may be used for preparing phenolic sheet molding compounds (SMC), has been investigated using a thermogravimetric analyzer and a differential scanning calorimeter. The weight loss of waterborne phenol-formaldehyde resin was mainly occurred at three temperature stages: near $200^{\circ}C,\;400^{\circ}C$, and $500^{\circ}C$. The carbon yield at $750^{\circ}C$ for the cured resin was about 62%~65%. Their thermal stability increased with increasing cure temperature and time. Upon cure, the exothermic reaction was taken placed in the range of $120^{\circ}C{\sim}190^{\circ}C$ and the maximum peak was found in between $165^{\circ}C$ and $170^{\circ}C$. The shape and the maximum of the exothermic curves depended on the given cure temperature and time. To remove $H_2O$ and volatile components, the uncured resin needed a heat-treatment at $100^{\circ}C$ for 60 min at least prior to cure or molding. Curing at $130^{\circ}C$ for 120 min made the exothermic peak of waterborne phenol-formaldehyde resin completely disappeared. And, post-curing at $180^{\circ}C$ for 60 min further improved the thermal stability of the cured resin.