Phenolic Foam Composites Research Articles

Lignin-Based Phenolic Foam Reinforced by Poplar Fiber and Isocyanate-Terminated Polyurethane Prepolymer.

Phenolic foams (PFs) are lightweight (<200 kg/m3), high-quality, and inexpensive thermal insulation materials whose heat and fire resistance are much better than those of foam plastics such as polyurethane and polystyrene. They are especially suitable for use as insulation in chemical, petroleum, construction, and other fields that are prone to fires. However, PFs have poor mechanical properties, poor abrasion resistance, and easy pulverization. In this paper, a polyurethane prepolymer was treated with an isocyanate, and then the isocyanate-terminated polyurethane prepolymer and poplar powder were used to prepare modified lignin-based phenolic foams (PUPFs), which improved the abrasion resistance and decreased the pulverization of the foam. The foam composites were comprehensively evaluated by characterizing their chemical structures, surface morphologies, mechanical properties, thermal conductivities, and flame-retardant properties. The pulverization ratio was reduced by 43.5%, and the thermal insulation performance and flame-retardancy (LOI) were improved. Compared with other methods to obtain lignin-based phenolic foam composites with anti-pulverization and flame-retardant properties, the hybrid reinforcement of foam composites with an isocyanate-terminated polyurethane prepolymer and poplar powder offers a novel strategy for an environmentally friendly alternative to the use of woody fibers.

The synthesis of DOPO-g-ESO and its effect on the properties of phenolic foam composites

In order to improve the properties of phenolic foam (PF), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was introduced into the structure of epoxidized soybean oil (ESO), and DOPO-grafted ESO (DOPO-g-ESO) was obtained to modify phenolic resin (PR) and to prepare modified PF (DEMPF). The structures of ESO and DOPO-g-ESO were verified by Fourier transform infrared spectroscopy and nuclear magnetic resonance. In comparison with ESO, DOPO-g-ESO shows slightly worse thermal stability; the initial decomposition temperature (Ti) and residual carbon (600°C) decreased by 18.3 and 5.57%, respectively. DOPO-g-ESO-modified PR (DEMPR) shows a slightly higher decomposition temperature in comparison with PR. The carbon residues (600°C) of DEMPR decreased with the increase in the DOPO-g-ESO/phenol (P) content. Moreover, with the increase in the DOPO-g-ESO/P content, the activation energies of DEMPR gradually increased, and the reaction orders were all non-integers. Compared with PF, when the dosage of DOPO-g-ESO/P was less than or equal to 10%, the mechanical properties of DEMPF improved and then deteriorated. However, the flame retardancy of DEMPF decreased slightly, but not too much. In addition, the cell sizes of DEMPF gradually increased. Using comprehensive analysis, the optimal dosage of DOPO-g-ESO/P was found to be about 10%.

Phenolic Resin Foam Composites Reinforced by Acetylated Poplar Fiber with High Mechanical Properties, Low Pulverization Ratio, and Good Thermal Insulation and Flame Retardant Performance.

Phenolic foam composites (PFs) are of substantial interest due to their uniform closed-cell structure, low thermal conductivity, and good thermal insulation performance. However, their disadvantages of a high pulverization rate and poor mechanical properties restrict their application in building exterior insulation. Therefore, the toughening of these composites is necessary. In this paper, poplar fiber was treated with an acetylation reagent, and the acetylated fiber was used to prepare modified phenolic foams (FTPFs); this successfully solved the phenomenon of the destruction of the foam structure due to the agglomeration of poplar fiber in the resin substrate. The foam composites were comprehensively evaluated via the characterization of their chemical structures, surface morphologies, mechanical properties, thermal conductivities, and flame retardant properties. It was found that the compressive strength and compressive modulus of FTPF-5% respectively increased by 28.5% and 37.9% as compared with those of PF. The pulverization ratio was reduced by 32.3%, and the thermal insulation performance and flame retardant performance (LOI) were improved. Compared with other toughening methods for phenolic foam composites, the phenolic foam composites modified with surface-compatibilized poplar fiber offer a novel strategy for the value-added utilization of woody fiber, and improve the toughness and industrial viability of phenolic foam.

Effects of Bamboo Fiber Length and Loading on Mechanical, Thermal and Pulverization Properties of Phenolic Foam Composites

In order to improve the mechanical properties and toughness of phenolic foams, a reinforcement method using two kinds of bamboo fibers was optimized with respect to the fiber contents. The compressive and flexural properties, thermal stability, friability and morphology of the phenolic foam composites were studied. The mechanical properties of the pristine foam and composites were evaluated by measuring the compressive strength. The results showed that the greatest mechanical properties were achieved by incorporating 2.5wt% of the reinforcement, and the compressive and flexural strengths of the two composites increased by 26.21% and 24.35%, respectively, compared with that of the pristine foam. The results of thermogravimetric testing demonstrated that the addition of bamboo fiber imparted better thermal stability to the phenolic foam, which was mainly attributed to the higher initial thermal decomposition temperature of the bamboo fiber. However, the influences of both reinforcements on the thermal stability of the material were negligible. The incorporation of bamboo fiber decreased the friability of the phenolic foam. Furthermore, the reduction in friability of the foam composites with longer lengths were higher than that in foams with shorter bamboo fibers. Moreover, the morphology and cell sizes of the fiber-reinforced phenolic foams were analyzed by scanning electron microscopy, the results indicated strong bonding between the fibers and phenolic matrix, and the incorporation of the bamboo fibers into the foam resulted in increased cell size of the material. Finally, the thermal conductivity and flame resistance of the phenolic foams reinforced by the bamboo fibers were also measured.

Preparation and Characterization of DOPO-ITA Modified Ethyl Cellulose and Its Application in Phenolic Foams.

In order to improve the performance of phenolic foam, an additive compound of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and Itaconic acid (ITA) were attached on the backbone of ethyl cellulose (EC) and obtained DOPO-ITA modified EC (DIMEC), which was used to modify phenolic resin and composite phenolic foams (CPFs). The structures of DOPO-ITA were verified by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H NMR). The molecular structure and microstructure were characterized by FT-IR spectra and SEM, respectively. Compared with EC, the crystallinity of DIMEC was dramatically decreased, and the diffraction peak positions were basically unchanged. Additionally, thermal stability was decreased and Ti decreased by 24 °C. The residual carbon (600 °C) was increased by 25.7%. With the dosage of DIMEC/P increased, the Ea values of DIMEC composite phenolic resins were increased gradually. The reaction orders were all non-integers. Compared with PF, the mechanical properties, flame retardancy, and the residual carbon (800 °C) of CPFs were increased. The cell size of CPFs was less and the cell distribution was relatively regular. By comprehensive analysis, the suitable dosage of DIMEC/P was no more than 15%.

Synthesis of DOPO‐g‐GPTS modified wood fiber and its effects on the properties of composite phenolic foams

ABSTRACTA novel 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) grafted γ‐glycidoxy propyl trimethoxy silane (GPTS) was synthesized and introduced on the surface of wood fiber (WF). DOPO‐g‐GPTS modified wood fiber (DGMWF) was then used to prepare DGMWF composite phenolic foam (DGMWFCPF). The structures of DOPO‐g‐GPTS were verified by Fourier transform infrared spectroscopy (FT‐IR) and nuclear magnetic resonance (1H‐NMR). The structure of DGMWF was confirmed by FT‐IR. The crystallinity of DGMWF was slightly increased, however, the diffraction peak positions were basically unchanged. In addition, the thermal stability was dramatically improved, and T i and Tmax increased by 26.6 and 33.2 °C respectively. The carbon residue (800 °C) was reduced by 3.65%. By comparison with pure phenolic foam, the mechanical properties, flame retardancy of DGMWFCPF were increased. No significant changes were observed for the microstructure. By comprehensive analysis, the interfacial compatibility was significantly improved between DGMWF and phenolic resin. The suitable dosage of DGMWF was 4–6%. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46917.

Effect of novel DOPO-g-coupling agent treated wood fibers on properties of composite phenolic foams

9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) graft γ-amino propyltriethoxy silane (APS), γ-glycidoxy propyltrimethoxy silane (GPS), and methacryloyl propyltrimethoxysilane (MPS) were synthesized and introduced on the surface of wood fiber. DOPO-g-APS (GPS and MPS) treated wood fibers (DAWF, DGWF, and DMWF) were used to prepare composite phenolic foams (DAWFCPF, DGWFCPF, and DMWFCPF). The chemical structures of DOPO-g-APS (GPS and MPS) were confirmed by Fourier transform infrared (FT-IR) spectra and nuclear magnetic resonance. The structures of DAWF, DGWF, and DMWF were confirmed by FT-IR. The diffraction peak positions were basically unchanged, but the crystallinity was slightly increased. Compared with WF, thermal stabilities were increased. The residue (800 °C) was slightly reduced. Compared with phenolic foam, the properties of DAWFCPF and DGWFCPF were better than others. Besides compression strength, the mechanical properties were increased dramatically, limited oxygen index was slightly enhanced, the cellular pore distribution was more regular, and the size of bubble cell was smaller and more uniform. By comprehensive analysis, the properties of DAWFCPF were best in all samples. The interfacial compatibility was significantly improved between DAWF and phenolic resin. These results confirmed that DOPO-g-APS is a suitable material for treating wood fibers and preparing composite phenolic foams.

A novel DOPO-g-KH550 modification wood fibers and its effects on the properties of composite phenolic foams

Abstract A novel 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) graft γ-amino propyl triethoxy silane (KH550) was synthesized and introduced on the surface of wood fiber. Finally DOPO-g-KH550 treated wood fiber (DKTWF) was used to prepare DKTWF composite phenolic foams (DKTWFCPF). The structures of DOPO-g- KH550 was acknowledged by Fourier transform infrared (FT-IR) and nuclear magnetic resonance (1H-NMR). The structures of DKTWF were confirmed by FT-IR. Compared with wood fiber, the diffraction peaks’ position was basically unchanged, but the crystallinity was slightly increased and thermal stability were dramatically improved, T5% and Tmax increased by 21.9o and 36.1o respectively. But the char yield (800o) was slightly reduced. With the dosage of DKWF, there were different degrees of improvement including the mechanical properties, flame retardancy and microstructure of DKTWFCPF. Comprehensive analysis, the interfacial compatibility was significantly improved between DKTWF and phenolic resin, and the suitable content of DKTWF was 4%.

The structure and properties of eucalyptus fiber/phenolic foam composites under N-β(aminoethyl)-γ-aminopropyl trimethoxy silane pretreatments

Abstract Eucalyptus fibers were modified with N-β(aminoethyl)-γ-aminopropyl trimethoxy silane to research the fiber surface’s changes and the influence of the treatment on the mechanical properties, flame resistance, thermal conductivity and microstructure of eucalyptus fiber composite phenolic foams (EFCPFs). The results showed that the partial of hemicelluloses, waxes, lignin and impurities from the fiber surface were dissolved and removed. Compared with untreated EFCPFs, the mechanical properties of treated EFCPFs were increased dramatically; The size of cells was smaller and the distribution was more uniform; The thermal conductivities were basically reduced; Especially the ratio of mass loss decreased obviously. However limited oxygen indexs (LOIs) reduced. And the mechanical properties and LOIs of EFCPFs were basically decreased with the increase of eucalyptus fibers. By comprehensive analysis, the results showed that the interfacial compatibility has been significantly improved between eucalyptus fibers and phenolic resin. And the suitable dosage of eucalyptus fibers was about 5%.

Morphologies and compression performance of graphene oxide/SiO2 modified phenolic foam

In this study, the graphene oxide/SiO2 hybrid materials with different sizes (GO/SiO2-80, GO/SiO2-170, GO/SiO2-250) were prepared via in situ preparation. Different sizes and weight fraction of GO/SiO2 were added into phenolic resin to prepare phenolic foam composites. The cell properties, morphologies, and mechanism of GO/SiO2 reinforced PF composites were studied. The results showed that the GO/SiO2-80 can improve the cell structure and compressive property obviously than other size nanoparticles. The PF modified with 1 wt% GO/SiO2-80 exhibited most uniform cell structure, and it showed a mean cell size of 117 µm and narrow cell size distribution from 50 µm to 225 µm. The obtained PF/(1 wt% GO/SiO2-80) also showed an excellent compressive strength and modulus of 0.18 and 3.22 MPa, which has increased by 80% and 61%, respectively, compared to the pure PF. This method may make it possible for using GO/SiO2 hybrid materials to enhance the cell structure and compression performance of the phenolic foam composites with broader applications.

Effects of Fiber Surface Treatments on the Properties of Wood Fiber–Phenolic Foam Composites

Wood fibers were modified with alkaline solution and silane coupling agent to study changes on the fiber surface and the influence of these treatments on the mechanical properties, flame resistance, thermal conductivity, and microstructure of wood fiber-phenolic foam composites. Test results indicated that the lignin, waxes, hemicelluloses, and other impurities from the fiber surface were partially dissolved and removed. The mechanical properties of treated wood fiber-phenolic foam composites increased dramatically, the cellular pore distribution was more regular, the size of bubble cells was smaller and more uniform, and the thermal conductivity was reduced, and, in particular, the fragility of treated wood fiber-phenolic foam composites decreased. However, with increasing wood fiber content, the mechanical properties and limited oxygen index (LOI) of composite foam decreased. By comprehensive analysis, it was shown that the interfacial compatibility between the fibers and phenolic resin was improved. Nevertheless, the amount of wood used could not be too high, and the optimum amount was approximately 5%.

Open-cell phenolic carbon foam and electromagnetic interference shielding properties

In this study, phenolic foam composites (PFC2Fs) with closed-cell structure consisting of multi-walled carbon nanotubes (MWCNTs) and nano-Fe3O4 were prepared via in-situ polymerization. The introduction of MWCNTs and nano-Fe3O4 can endow the PF with electromagnetic interference (EMI) shielding property. The sample with 2 wt% MWCNTs and 7 wt% Fe3O4 (PFC2F7) with thickness of 2 mm exhibited the EMI shielding effectiveness (SE) with ∼34 dB at 8–12 GHz. Furthermore, novel high-performance carbonized PF/2 wt% MWCNTs/Fe3O4 composite foams (C-PFC2Fs, carbon foam) with open-cell structure were fabricated by using high-temperature heat treating method. The obtained C-PFC2F7 exhibited the highest EMI SE of ∼62 dB at 8–12 GHz. The shielding mechanism of MWCNTs and nano-Fe3O4 was investigated. The method is fast and simple, which may promote the commercialization of composite foams in the potential applications as EMI shielding materials in the fields of spacecraft and aircraft.

Effect of multi-walled carbon nanotubes on mechanical, thermal and electrical properties of phenolic foam via in-situ polymerization

In this study, phenolic foam (PF)/multi-walled carbon nanotubes (MWCNTs) composites were fabricated by in-situ polymerization, and carbonized foams based on these PF foams were prepared and the electrical property was investigated. TEM results indicated excellent dispersion of MWCNTs in the phenolic resin matrix. Scanning electron microscope results indicated that PF composites exhibited smaller cell size, thicker cell wall thickness, and higher cell density, compared with pure PF. The incorporating of MWCNTs significantly improved the mechanical properties of PF. All PF composites showed a lower thermal conductivity versus pure PF. Moreover, the carbonized pure and composites PF exhibited open-cell three-dimensional skeleton carbon structure and the MWCNTs were well-dispersed on the surface of the skeletons. It is noteworthy that the introduction of MWCNTs significantly improved the electrical performances of foams and carbonized foams by construction of conductive MWCNTs network.

Effect of zinc oxide on properties of phenolic foams/halogen‐free flame retardant system

ABSTRACTA halogen‐free flame retardant system consisting of ammonium polyphosphate (APP) as an acid source, blowing agent, pentaerythritol (PER) as a carbonific agent and zinc oxide (ZnO) as a synergistic agent, was used in this work to enhance flame retardancy of phenolic foams. ZnO was incorporated into flame retardant formulation at different concentrations to investigate the flammability of flame retardant composite phenolic foams (FRCPFs). The synergistic effects of ZnO on FRCPFs were evaluated by limited oxygen index (LOI), thermogravimetric analysis (TGA), cone calorimeter tests, and images of residues. Results showed that the flame retardant significantly increased the LOI of FRCPFs. Compared with PF, heat release rate (HRR), total heat release (THR), effective heat of combustion (EHC), production or yield of carbon monoxide (COP or COY) and Oxygen consumption (O2C) of FRCPFs all remarkably decreased. However specific extinction area (SEA) and total smoke release (TSR) significantly increased, which agreed with the gas‐phase flame retardancy mechanism of the flame retardant system. The results indicated that FRCPFs have excellent fire‐retardant performance and less smoke release. And the bending and compression strength were decreased gradually with the increase of ZnO. The comprehensive properties of FRCPFs were better when the amount of ZnO was 1∼1.5%. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42730.

Mechanical and Thermal Properties of Phenolic Foams Reinforced by Hollow Glass Beads

Hollow glass beads / phenolic foam composites were prepared by molding method. The influence of HGB on thermal performance and mechanical properties of phenolic foams were investigated using thermal conductivity measurement, thermogravimetric analysis (TGA) and compression tester. The results show that the addition of hollow glass beads lead to a significant improvement in the compressive property of phenolic foams, with the compressive strength reaching the maximum adding 10% HGB and HGB pretreated by silicane coupling agent further enhance the compressive property. FT-IR spectroscopy shows the reaction between alcohol-OH groups on the surface of HGB and methoxy (-OCH3) groups on silane coupling agent (KH560). The morphology indicates the average cell size decreases with HGB content increasing up to 10%, and again the cell size of foams reinforced by pretreated HGB are better. Addition of HGB improved the thermal stability property of phenolic foams, due to the porosity was mainly responsible for thermal conductivity property of phenolic foams, so HGB filled materials achieved higher thermal conductivity.

Preparation and characterization of phenolic foams with eco-friendly halogen-free flame retardant

The high solid resol phenolic resin was prepared via step polymerization of formaldehyde, paraformaldehyde, and phenol using sodium hydroxide and calcium oxide as catalysts, and employed to prepare the phenolic foams (PFs) by the introduction of retardant additives including eco-friendly halogen-free flame retardants (ammonium polyphosphate), char-forming agents (pentaerythritol), and synergists (zinc oxide, molybdenum trioxide, cuprous chloride, and stannous chloride). The effects of these additives on flame retardancy, heat resistance, and fire properties of flame-retardant composite phenolic foams (FRCPFs) were evaluated by limiting oxygen index (LOI) tests, thermogravimetric analyzer, and cone calorimeter tests. It was found that the flame retardan significantly increased the LOIs of FRCPFs. Compared with PF, heat release rate, total heat release, effective heat of combustion, production or yield of carbon monoxide (COP or COY), and Oxygen consumption (O2C) of FRCPFs all remarkably decreased. However specific extinction area and total smoke release significantly increased, which agreed with the gas-phase mechanism of the flame-retardant system. The results indicate that FRCPFs have excellent fire-retardant performance and less smoke release. APP/PER/ZnO is shown to be better flame-retardant system for PFs.

Diffusivity and Climatic Simulation of Hybrid Foams

Hybrid composite phenolic foams reinforced with glass and aramid fibers were prepared and evaluated as potential materials for insulation and cladding applications. In particular, moisture uptake, flammability, and accelerated aging experiments were performed. A statistical approach was employed to model and predict the moisture absorption of the foams. Hybrid foams exhibited much lower diffusivity of water molecules and moisture content compared to unreinforced foam. The properties of hybrid foams were also compared to commercial expanded polystyrene (EPS) foam. The flammability properties of hybrid foams were markedly superior to EPS. Accelerated aging test revealed excellent dimensional stability of hybrid foams even under extreme conditions. Compressive stiffness of hybrid foams was retained even after aging.

Mechanical Behavior of Hybrid Composite Phenolic Foam

Hybrid composite phenolic foams are reinforced with chopped glass and aramid fibers in varied proportions. The mechanical properties are measured and compared with those of foams reinforced with only aramid and glass fibers. The compression and shear properties of the hybrid reinforced foams are also compared with those of commercial polyurethane foams. The reinforced hybrid phenolic foams exhibit greater resistance to cracking and are significantly stiffer and stronger than foams with only glass and Nomex® fibers. In general, the mechanical properties of reinforced hybrid phenolic foams are comparable to that of commercial polyurethane foam of equivalent density. The experimentally observed compressive properties (compression modulus) of reinforced phenolic foam with different fiber loading have been compared with existing theories of reinforcement. Composite models such as parallel, series, Halpin—Tsai, and the Hirsch model have been evaluated to fit the experimental data. The findings presented here, coupled with earlier results, demonstrate the potential use of hybrid composite foams as a low-cost engineering material that is tough, strong, and fire retardant.

Analysis of pulling force during pultrusion process of phenolic foam composites

An analysis was carried out to predict the pulling force during the pultrusion process of phenolic foam composites. Pulling force for foamed composites is considerably higher than composites without foam due to the pressure exerted by expanding bubbles. In order to model the process, the pressure applied on both tapered and flat regions of the heated die wall was estimated by one-dimensional porous medium flow model. For solidified matrix after the gel point, the energy equation and the thermoelastic problem considering the pressure of growing bubbles were solved together using the finite element method. For experimental study, a lab-scale pultrusion apparatus was constructed. Pulling force was measured by a load cell during the process. Methylene chloride (CH 2Cl 2) was used as the physical blowing agent and glass fiber roving was employed as the reinforcement. Matrix resin was a Resol type phenolic resin. The numerical results were compared with the experimental data for different process variables such as temperature, amount of blowing agent and pulling speed. Close agreement between the experimental data and the numerical results was observed.

Analysis of bubble nucleation and growth in the pultrusion process of phenolic foam composites

A study was carried out to analyze the foaming characteristics in the pultrusion process of phenolic foam composites. For the experimental study, a lab-scale pultrusion apparatus was constructed. Glass fiber roving and a resol type phenolic resin were used as reinforcement and matrix, respectively. Methylene chloride (CH 2Cl 2) was employed as a physical blowing agent. The number and the average size of bubbles were measured using a scanning electron microscope and an image analyzer. For the theoretical analysis, a model that combines classical heterogeneous nucleation with bubble growth in a gradually hardening resin was considered. The process variables considered were the pulling speed, the die wall temperature and the mass fraction of blowing agent. A computer code was written to solve a system of equations from the model. Numerical results were compared with the experimental data for different process variables. Close agreement was observed.