Neat PF Research Articles

Improved flame retardancy and smoke suppression properties of phenolic resin by incorporating MoO3 particles

Phenolic resin (PF) is widely used in aerospace, composite materials, and other fields. However, large amount of heat and smoke are produced during its combustion process, which is an important factor limiting its usage. To solve this problem, additive flame retardant MoO3 has been incorporated into PF for improving its flame retardancy and smoke suppression properties. Thermogravimetric analyses results show that the T5% of PF composites was gradually decreased from 264°C to 184°C and the char yield of PF-10% MoO3 is 57 wt.%, higher than that of neat PF (50 wt.%). The PF composites with 10 wt.% MoO3 passed UL-94 V-0 rating with a limiting oxygen index value of 29.8%. Meanwhile, the total heat release and total smoke production of PF-10% MoO3 are 37.60 MJ/m2 and 5.79 m2 respectively, which are reduced by 30.5% and 24.8% compared with neat PF. Only 10 wt.% MoO3 provide a 56.5% reduction (from 255 to 111) in maximal smoke density, meaning the good smoke suppression properties of MoO3. The pyrolysis products components are determined by thermogravimetric analysis combined with Fourier transform infrared spectroscopy. Furthermore, the micromorphology and chemical structure of char residue are also investigated by scanning electron microscopy, x-ray diffraction and Raman spectroscopy techniques. The promoting carbonization effect of MoO3 significantly reduces the heat release and toxic smoke production of PF composites.

Bio-oil-based phenol–formaldehyde resin: comparison of weight- and molar-based substitution of phenol with bio-oil

The objectives of this study were (i) to synthesize bio-oil-based phenol–formaldehyde resin to be used for the wood products industry, and (ii) to investigate the effect of phenol substitution (molar-based vs. weight-based) with bio-oil on the properties of resulting PF resin. Bio-oil was produced by hydrothermal liquefaction (HTL) process using sweetgum hardwood, and utilized as a bio-based phenolic feedstock as an alternative for petroleum-based phenol in the synthesis of PF resin. Phenol was substituted with bio-oil (both as weight- and molar-based). The resulting PF resin was noted as BPF-W and BPF-M when bio-oil was used to replace 50% of phenol in weight- and molar-based, respectively, and then compared with neat PF resin in terms of free formaldehyde content, gel time, pH of the resin, solid content, bond strength and thermal stability. Results showed that BPF-M resin had less free formaldehyde content and longer gel time than BPF-W resin. No significant difference in pH and solid content was observed between bio-oil-based PF resins. Moreover, molar-based substitution resulted in a resin with higher bonding strength than that of weight-based substitution, and both BPF-W and BPF-M showed higher bonding strength then neat PF resin. TGA analysis of the resin revealed that substitution of phenol with bio-oil lowered the thermal stability of bio-oil derived PF resins. However, molar-based substitution of phenol with bio-oil could enhance the thermal stability.

Influence of the Addition of Nano-porous Graphite/Parafffin Additive on the Wear Properties of Phenol-Formaldehyde Resin Composites

Phenol-formaldehyde resin (PF) composites with a nano-porous graphite additive (NPGA) in various contents were fabricated and the wear behaviors under low and high sliding speeds were studied. The addition of NPGA significantly improved the wear resistance of the PF. The specific wear rates of PF composites under low sliding speed first decreased with increasing NPGA and then slightly increased when the NPGA content surpassed 15 wt%; the specific wear rate of the composite with 15 wt% NPGA was reduced by 77% compared with the neat PF. Under high sliding speed the specific wear rates of the composite material decreased continuously with increasing NPGA content and the maximum wear resistance of the composite with 20 wt% NPGA was more than 12 times that of the neat phenolic resin. The results are attributed to the combined effects of load-capacity and the lubrication role of the included NPGA. The surface morphology of the worn surface was characterized, and the wear mechanism for the composites is discussed.

The Synergistic Effects of Multi-Filler Addition on the Mechanical and Thermo-Mechanical Properties of Phenolic Resins

The effects of the carbon fiber (CF), carbon black (CB) and nanosilica (SiO2) on the mechanical properties of the phenolic resin (PF) were studied and the optimum composition was selected for the preparation of quaternary composites (CF/CB/SiO2 phenolic composites). The incorporation of poly (acrylonitrile-co-butadiene) rubber (NBR) to strengthen the quaternary composites were also studied. The morphological, mechanical and thermo-mechanical properties of unmodified and NBR modified-quaternary phenolic composites were investigated. The phenolic compounds were mixed by ball milling and the phenolic composites were fabricated by hot compression molding. Scanning electron microscopy images of NBR modified-quaternary phenolic composites show the high fracture surface roughness. The results show that the addition of 5 wt% NBR in the quaternary composites offer the highest tensile strength and Young’s modulus which are significantly improved by 176% and 235%, respectively, and they also offer the high flexural strength, impact strength and flexural modulus which are improved by 79%, 29% and 12%, respectively, compared to neat PF. The glass transition temperature (Tg) of unmodified and NBR modified-quaternary phenolic composites are higher than that of neat PF (107.3 °C). The increase of NBR content does not deteriorate Tg of the quaternary phenolic composites. This study provides a new pathway for making advanced phenolic composites.

Situ preparation of SiO2 on graphene-assisted anti-oxidation for resol phenolic resin

Easily oxidized group of traditional phenolic resin (PF) results in poor oxidation resistance at high temperature, which is unable to satisfy the requirements of advanced aerospace vehicles for high-performance application, especially ablation resistance. In order to improve the oxidation resistance of PF, a SiO2/RGO binary hybrid nanomaterial assisted anti-oxidation for PF was designed. Here, we reported a simple sol-gel process and high temperature reduction for synthesis of dispersed SiO2 nanoparticles on graphene (G-S). The designed structure of G-S was confirmed by FTIR, XRD, SEM and TEM. Introduction of G-S into PF (P-G-S) was beneficial to enhancement of oxidation resistance in whole temperature range (0–1000 °C). P-G-S-3 (3 wt.% of G-S) exhibits both lower thermal oxidative decomposition rate and higher termination temperature of thermal oxidative decomposition (increase from about 750 °C up to 900 °C) than those of neat PF in air. In addition, P-G-S-3 decomposed by thermal oxidation in air (at 557 °C, weight loss> 30 wt.%) later than neat PF (at 519 °C, weight loss> 20 wt.%). What's more, compared to the collapse of skeleton structure and few residual fragments of neat PF, P-G-S-3 showed greater oxidation resistance which resulted in the retention of a large number of aromatic C-C, methylene and different kinds of ether bond at temperature from 550 °C to 700 °C by FTIR and XPS. The section of P-G-S-3 expresses skin lamination that can act as a barrier to slow down the diffusion of oxygen into resin matrix. And SiO2 on the surface protected the matrix continually as indicated from the SEM analysis.

Lignins from enzymatic hydrolysis and alkaline extraction of steam refined poplar wood: Utilization in lignin-phenol-formaldehyde resins

In this study, a steam refining process, optimized earlier with respect to carbohydrate yield, was used to extract lignins from non-debarked poplar wood from short growth plantations by enzymatic hydrolysis (EHL) and alkaline extraction (AEL) for the utilization in lignin-phenol-formaldehyde resins (LPF). Three different pretreatment conditions were chosen at 190°C and 16min, 210°C and 15min and 200°C, 15min, 2.5% SO2. Characterization of the lignins revealed that the carbohydrate content decreased about 47% (210°C, 15min) to 58% (200°C, 15min, 2.5% SO2) with intensification of the pretreatment conditions. Furthermore, the average molecular weight and polydispersity increased. The chemical and physico-chemical properties of lignin-phenol-formaldehyde resins synthesized with these lignins were evaluated and gluebond performance was tested by the Automated Bonding Evaluation System (ABES). LPF resins with AEL and EHL (190°C, 16min) were used to produce particleboards. LPF resins with Organosolv lignin (OL) and Kraft lignin as well as neat PF resins served as references. The mechanical properties of these panels were evaluated. The results showed high dry (EHL: 0.64Nmm−2, AEL: 0.73Nmm−2) and wet internal bond strength (EHL: 0.21Nmm−2, AEL: 0.25Nmm−2) of LPF bonded particleboards. LPF resin with AEL fulfills the requirements for the relevant standard specifications P7 according to DIN EN 312:2010-12.

Effects of bark extraction before liquefaction and liquid oil fractionation after liquefaction on bark-based phenol formaldehyde resoles

Liquid product from white birch bark liquefaction in water/ethanol (50:50, v/v) mixture was successfully applied in substituting 50wt% of phenol in the synthesis of bark based phenol formaldehyde (BPF) resole (i.e., 50% HTL-oil BPF resole). Besides, eHTL-oil from liquefaction of the bark extracted in 70vol% aqueous acetone, and fHTL-oil obtained after HTL-oil fractionation in water, were also used to substitute 50% of phenol for BPF resoles synthesis. The results showed that all the three BPF resoles contained more free formaldehyde than the neat PF resole, and bark extraction before liquefaction and HTL-oil fractionation after liquefaction led to higher free formaldehyde contents in the resulted 50% eHTL-oil BPF resole and 50% fHTL-oil BPF resole. Furthermore, bark extraction before liquefaction retarded the curing of the resulted 50% eHTL-oil BPF resole, while HTL-oil fractionation after liquefaction slightly promoted the curing of the resulted 50% eHTL-oil BPF resole. All the three BPF resoles displayed less thermal stability than the neat PF resole, but the effects of bark extraction before liquefaction and HTL-oil fractionation after liquefaction on the thermal stability of the resulted BPF resoles were negligible. All the three BPF resoles could meet the bond strength requirements as adhesives for plywood in accordance to the JIS standard. Bark extraction before liquefaction led to less water resistance for the resulted 50% eHTL-oil BPF resole, while HTL-oil fractionation after liquefaction improved the water resistance of the resulted 50% fHTL-oil BPF resole.

Thermal Properties and Mechanical Performance of Unsaturated Polyester/Phenolic Blends Reinforced by Kenaf Fiber

In this study, unsaturated polyester resin (UP) is blended with resole type phenolic resin (PF) to develop a material with good flame retardancy. The UP/PF resin blends are expected to show good compatibility when compounded with natural fibers which in this research is kenaf fiber. The thermal properties were investigated by thermogravimetric analysis (TGA). The char yields of the UP/PF blends reinforced kenaf composite increased with PF content. The degradation temperature of the composite at 50% weight loss rose to 410.13°C as the PF content was increased to 40%. The result shows with additional of PF to UP resin enhance the thermal stability of the composite. Meanwhile the mechanical performance of UP/PF kenaf composite were evaluated and compared with neat UP and PF reinforced with kenaf fiber using tensile and impact testing. The mechanical properties of all resin blends at different mixing proportions slightly decrease by increasing the phenolic content but shown an improvement as compared to the PF kenaf fiber composite. The fracture surface morphology of the tensile testing samples of the composites was performed by scanning electron microscopy (SEM).

Thermal degradation performance of bark based phenol formaldehyde adhesives

Neat phenol formaldehyde adhesive (neat PF), bark bio-crude synthetic bio-based phenol formaldehyde adhesive (bio-crude synthetic BPF) in which 50% phenol was substituted by bio-crude during synthesis, bark bio-crude formulated bio-based phenol formaldehyde adhesive (bio-crude formulated BPF) that was prepared through direct blending of aqueous bio-crude with neat PF at the weight ratio of 50:50, and bark extractives synthetic bio-based phenol formaldehyde adhesive (extractive synthetic BPF) in which 50% phenol was substituted by alkali extractives during synthesis were characterized by thermogravimetry analyzer coupled to Fourier transform infrared spectroscopy (TGA/FTIR), to investigate the stability, thermal degradation kinetics, structure change and the evolved gaseous products. It was found neat PF and BPFs all went through typical three stages degradation. Introduction of bio-crude into BPF reduced the thermal stability for the resulted BPF to a greater extent than extractive introduction. With respect to residual weight after degradation at 800°C, adhesives thermal stability followed the order: neat PF>extractives synthetic BPF≫bio-crude formulated BPF>bio-crude synthetic BPF, which is consistent with the activation energy for the adhesives degradation in the main degradation stage. Auto-oxidation occurred during all the adhesive thermal degradation. But bio-crude based BPFs are more auto-oxidation resistant than neat PF or extractive synthetic BPF. Gaseous products evolved from neat PF degradation mainly consisted of water, phenol, cresol, CO2, CH4, CO and carboxylic acids. During BPFs degradation, CH4, phenol, cresol were yielded at lower temperatures than neat PF degradation. Besides, xylenol not yielded during neat PF degradation was evolved from BPF degradation.

Adhesives formulated from bark bio-crude and phenol formaldehyde resole

Rather than replacing phenol in the synthesis of PF resole, bark-derived bio-crudes were used as an adhesive constituent by simply formulation with neat PF adhesive in this study. Bio-crude derived from white birch bark (WBB)—a typical hardwood bark and white spruce bark (WSP)—a typical softwood bark were blended with neat PF adhesive to prepare bark bio-crude formulated bio-phenol formaldehyde (BPF) adhesive (designated as bio-crude formulated BPF adhesive). It was discovered that the viable formulation ratio between bark bio-crude and neat PF adhesive depended on the bark species. WBB bio-crude could be formulated with neat PF adhesive at a formulation ratio of 50:50 (wt/wt), while WSP bio-crude can be formulated with neat PF adhesive at a higher formulation ratio up to 75:25 (wt/wt). The peak curing temperatures of the bio-crude formulated BPF adhesives were lower than that of neat PF adhesive. Activation energy for the curing of WBB bio-crude formulated BPF adhesives was higher than that for the curing of neat PF adhesive, while WSP bio-crude formulated BPF adhesive required less activation energy for curing than neat PF adhesive. Condensation between bio-crude and neat PF adhesive occured during the pre-curing process at 125°C and was confirmed by FTIR spectra. Interestingly, the introduction of bio-crude enhanced the thermal stability of the bio-crude formulated BPF adhesives at low temperatures, but as expected, thermal stability of the bio-crude formulated BPF adhesives reduced at higher temperatures and a higher formulation ratio led to lower thermal stability. At a same formulation ratio, WSP bio-crude formulated BPF adhesives showed better thermal stability than WBB bio-crude. More interestingly, the free formaldehyde emission level of 3-ply plywood bonded by bio-crude formulated BPF adhesives, in particular with the WSP bio-crude, was lower than that of the neat PF adhesive bonded plywood. Free formaldehyde emission levels from 3-ply plywood bonded with WSP bio-crude formulated BPF adhesives at the formulation ratios of 50:50 (wt/wt) and 75:25 (wt/wt) reached JIS F*** level. However, bio-crude formulated BPF adhesives reduced the tension shear strength of bonded 3-ply plywood, in particular at higher formulation ratios. At the same bio-crude formulation ratio, WSP bio-crude formulated BPF adhesives gave better tension shear strength for 3-ply plywood than the WBB bio-crude formulated BPF adhesives. Nevertheless, 3-ply plywoods bonded with bark bio-crude formulated BPF adhesives at a ratio up to 50:50 (wt/wt) still met the JIS standards with respect to tension shear strength.

In situ chemical reduction and functionalization of graphene oxide for electrically conductive phenol formaldehyde composites

We report an efficient one-step approach to reduce and functionalize graphene oxide (GO) during the in situ polymerization of phenol and formaldehyde. The hydrophilic and electrically insulating GO is converted to hydrophobic and electrically conductive graphene with phenol as the main reducing agent. Simultaneously, functionalization of GO is realized by the nucleophilic substitution reaction of the epoxide groups of GO with the hydroxyl groups of phenol in an alkali condition. Different from the insulating GO and phenol formaldehyde resin (PF) components, PF composites are electrically conductive due to the incidental reduction of GO during the in situ polymerization. The electrical conductivity of PF composite with 0.85vol.% of GO is 0.20S/m, nearly nine orders of magnitude higher than that of neat PF. Moreover, the efficient reduction and functionalization of GO endows the PF composites with high thermal stability and flexural properties. A striking increase in decomposition temperature is achieved with 2.3vol.% of GO. The flexural strength and modulus of the PF composite with 1.7vol.% GO are increased by 316.8% and 56.7%, respectively.

Synergistic effect of boron nitride flakes and tetrapod-shaped ZnO whiskers on the thermal conductivity of electrically insulating phenol formaldehyde composites

Tetrapod-shaped zinc oxide (T-ZnO) whiskers and boron nitride (BN) flakes were employed to improve the thermal conductivity of phenolic formaldehyde resin (PF). A striking synergistic effect on thermal conductivity of PF was achieved. The in-plane thermal conductivity of the PF composite is as high as 1.96Wm−1K−1 with 30wt.% BN and 30wt.% T-ZnO, which is 6.8 times higher than that of neat PF, while its electrical insulation is maintained. With 30wt.% BN and 30wt.% T-ZnO, the flexural strength of the composite is 312.9% higher than that of neat PF, and 56.2% higher that of the PF composite with 60wt.% BN. The elongation at break is also improved by 51.8% in comparison with that of the composite with 60wt.% BN. Such a synergistic effect results from the bridging of T-ZnO whiskers between BN flakes facilitating the formation of effective thermal conductance network within PF matrix.

Modified Phenolic Resins Based on Hyperbranched Polysiloxane with Improved Thermal Stability and Flame Retardancy

A novel modified phenolic (PF) resin with high performance was developed, which was prepared by hybranched phenyl polysiloxane (HPSi) synthesized by our research group with PF resin. The effect of the incorporation of HPSi into PF resin on typical performance of HPSi/PF resins were systemically discussed. Results show that the incorporation of HPSi can not only effectively promote the thermal properties, but also improve the flame retardancy. For example, in the case of the modified PF resin with 10wt% HPSi, initial decompose temperature (Tdi) of HPSi is at about 405°C, which is 18°C more than that of neat PF resin at the heating rate of 10°C/min; its char yield at 800°C increases from 68.9% to 76.2% at the heating rate of 10°C/min. What’s more, HPSi10/PF resin has the maximum LOI value, which is 14.6% more than that of neat PF resin. The novel modified PF resin with improving integrated properties exhibits great potential to be used for many cutting-edges fields.

Preliminary Study on Chicken Feather Protein–Based Wood Adhesives

The objective of this preliminary study was to partially replace phenol in the synthesis of phenol-formaldehyde resin with feather protein. Feather protein–based resins, which contained one part feather protein and two parts phenol, were formulated under the conditions of two feather protein hydrolysis methods (with and without presence of phenol during hydrolysis), two formaldehyde/phenol molar ratios (1.8 and 2.0), and three pH levels (9.5, 10.5, and 11.5). Southern pine fiberboard bonded with feather protein–based resins was fabricated and bending strength, bending stiffness, internal bonding strength, and percent thickness swell were evaluated. Results indicated that the test parameters all significantly affected resin quality. The resin formulated with feather protein hydrolyzed in the presence of phenol, using a F/P ratio of 2.0, and at a pH of 10.5 performed as well as the neat PF resin. Based on our findings, feather protein is a potential cost-effective material for the production of PF-type adhesive resins.

Effect of chemical modifications on the thermal stability and degradation of banana fiber and banana fiber‐reinforced phenol formaldehyde composites

AbstractBanana fiber has been modified by treatments with sodium hydroxide, silanes, cyanoethylation, heat treatment, and latex treatment and the thermal degradation behavior of the fiber was analyzed by thermogravimetry and derivative thermogravimetry analysis. Both treated and untreated fibers showed two‐stage decomposition. All the treatments were found to increase the thermal stability of the fiber due to the physical and chemical changes induced by the treatments. The thermal degradation of treated and untreated banana fiber‐reinforced phenol formaldehyde composites has also been analyzed. It was found that the thermal stability of the composites was much higher than that of fibers but they are less stable compared to neat PF resin matrix. Composite samples were found to have four‐stage degradation. The NaOH treated fiber‐reinforced composites have very good fiber/matrix adhesion and hence improvement in thermal stability is observed. Though both silane treatments increased the thermal stability of the composite the vinyl silane is found to be more effective. Heat treatment improves the crystallinity of the fiber and decreases the moisture content, hence an improved thermal stability. The latex treatment and cyanoethylation make the fiber surface hydrophobic, here also the composite is thermally more stable than untreated one. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Morphological Analysis of PF/pMDI Hybrid Wood Adhesives

Simple blends of polymeric methylenebis(phenylisocyanate), pMDI, dispersed in aqueous phenol formaldehyde, PF, were studied to determine how the emulsion structure impacted the resulting solid-state morphology. Shortly after mixing, optical microscopy of the liquid emulsions revealed rapid membrane formation around the dispersed pMDI droplets. This membrane appeared to arise from the pMDI/PF reaction and not from the pMDI/H2O reaction. Field emission scanning electron microscopy (FE/SEM) and atomic force microscopy (AFM) of partially cured blends detected a pMDI-borne dispersed phase exhibiting a sharp phase boundary. AFM revealed a halo surrounding the dispersed phase. This halo feature extended into the PF continuous phase; it was interpreted as evidence for a copolymeric region, suggesting that pMDI diffused into the continuous phase. Dynamic mechanical analysis of the partially cured blends revealed two overlapping secondary transitions, interpreted as phenolic relaxations from neat PF and separately from a PF/pMDI copolymer. Supporting the putative copolymer formation is the fact that the pMDI dispersed phase is associated with accelerated cure in comparison to neat PF. Collectively, the results indicate that the liquid emulsion morphology is largely preserved in the resulting solid, but that some interdiffusion occurs between phases during cure. The resulting copolymer formation accelerates cure and possibly enhances toughness near the phase boundary.

Fine Structure of Fluorinated Copolymer / Nano-filler Composites

Fine structure in the matrix polymer and dispersion state of fillers for poly [tetrafluoroethylene-co-(perfluoroalkylvinylether)] (abbrev. PFA) I nano-fillers (such as organo-modified smectite, organo-modified mica, and porous silica particles) composites were investigated by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). From the results of TEM observation, it was found that nano-fillers were almost uniformly dispersed in PF A matrix. Further, PFA I nano-filler composites are exhibited relatively larger distance between lamellar gravity at least 30 nm estimated by SAXS than general hydrogenated crystalline polymer. This result means that fluorinated copolymer formed the thicker lamella crystal. In addition, a melting peak these nanocomposites showed in DSC thermograms was shifted to higher temperature side than that of neat PF A. It is suggested that the origin of this thermal behavior corresponds to occurrence the nucleator effect of nano-fillers to the matrix PFA.