Novel phenolic resins with improved mechanical and toughness properties

Enhanced electrocatalytic removal of bisphenol a by introducing Co/N into precursor formed from phenolic resin waste

Bisphenol A (BPA) is a typical endocrine disruptor, which can be used as an industrial raw material for the synthesis of polycarbonate and epoxy resins, etc. Recently, BPA has appeared on the list of priority new pollutants for control in various countries and regions. In this study, phenolic resin waste was utilized as a multi-carbon precursor for the electrocatalytic cathode and loaded with cobalt/nitrogen (Co/N) on its surface to form qualitative two-dimensional carbon nano-flakes (Co/NC). The onset potentials, half-wave potentials, and limiting current densities of the nitrogen-doped composite carbon material Co/NC in oxygen saturated 0.5 mol H2SO4 were -0.08 V, -0.61 V, and -0.41 mA cm-2; and those of alkaline conditions were -0.65 V, -2.51 V, and -0.38 mA cm-2, and the corresponding indexes were improved compared with those of blank titanium electrodes, which indicated that the constructed nitrogen-doped composite carbon material Co/NC was superior in oxygen reduction ability. The catalysis by metallic cobalt as well as the N-hybridized active sites significantly improved the efficiency of electrocatalytic degradation of BPA. In the electro-Fenton system, the yield of hydrogen peroxide generated by cathodic reduction of oxygen was 4.012 mg L-1, which effectively promoted the activation of hydroxyl radicals. The removal rate of BPA was above 95% within 180 min. This work provides a new insight for the design and development of novel catalyst to degrade organic pollutants.

Influence of dodecyl surfactants on the cross-linking, plasticization and damping behavior of epoxy novolac resins

A series of modified epoxy novolac resins (ENRs) were prepared by incorporating dodecyl chain surfactants with polar groups such as amine, carboxylic acid, phenol, resorcinol and benzene sulfonic acid. Except for the case of benzene sulfonic acid, no macrophase separation is seen in any of the modified ENRs. The addition of these dodecyl surfactants to ENR hinders the cross-linking reaction as revealed from their dynamic and isothermal DSC curing measurements and reduced glass transition temperatures (T_g). The cross-link density evaluated from the storage modulus (E') in the rubbery region using DMTA measurements is found to be low with the addition of surfactants in agreement with their plasticization behavior. The stiffness of the materials obtained at low temperatures showed a moderate increase for ENRs with carboxylic acid and phenol surfactants. Upon heating, their storage modulus drops at low temperatures compared to ENR supporting the mechanism of plasticization in them. This high value of E' for the plasticized material in the glassy phase is different from the generally known behavior. Such unusually high storage modulus together with increased 'd' spacing from the XRD results seems to indicate 'partial segmental confinement' of epoxy chains. It is believed that high damping obtained in these two materials is due to 'partial segmental confinement' of epoxy chains because of interaction with lauric acid and phenolic surfactants and the associated internal and interfacial friction in them. Dielectric relaxation measurements support the plasticization process based on the high dielectric loss and ionic conductivity in the surfactant modified ENR, as compared to the pristine ones.

Identification by GC-MS Analysis of Organics in Manufactured Articles through a D-Optimal Design

Many manufactured articles are made of composite materials often bonded by a phenolic resin. Through a D-optimal design, we optimized a method to characterize phenolic resins after the extraction process by GC-MS analysis. The study was conducted on three different phenolic resins and four manufactured articles with the same inorganic composition and different analyzed binders. Moreover, three cardanol resins that differ in their production systems were analyzed to see if there were differences between them. Through Soxhlet extraction with dichloromethane or acetone, it is possible to differentiate the raw materials through characteristic compounds and to identify them in the manufactured articles.

Effect of Cyrtostachys renda Fiber Loading on the Mechanical, Morphology, and Flammability Properties of Multi-Walled Carbon Nanotubes/Phenolic Bio-Composites

This research focuses on evaluating the effect of Cyrtostachys renda (CR) fiber and the impact of adding multi-walled carbon nanotubes (MWCNT) on the morphological, physical, mechanical, and flammability properties of phenolic composites. MWCNT were supplemented with phenolic resin through a dry dispersion ball milling method. Composites were fabricated by incorporating CR fiber in 0.5 wt.% MWCNT-phenolic matrix by hot pressing. Nevertheless, the void content, higher water absorption, and thickness swelling increased with fiber loading to the MWCNT/phenolic composites. The presence of MWCNT in phenolic enhanced the tensile, flexural, and impact strength by as much as 18%, 8%, and 8%, respectively, compared to pristine phenolic. The addition of CR fiber, however, strengthened MWCNT-phenolic composites, improving the tensile, flexural, and impact strength by as much as 16%, 16%, and 266%, respectively, for 50 wt.% loading of CR fiber. The CR fiber may adhere properly to the matrix, indicating that there is a strong interface between fiber and MWCNT-phenolic resin. UL-94 horizontal and limiting oxygen index (LOI) results indicated that all composite materials are in the category of self-extinguishing. Based on the technique for order preference by similarity to the ideal solution (TOPSIS) technique, 50 wt.% CR fiber-reinforced MWCNT-phenolic composite was chosen as the optimal composite for mechanical and flammability properties. This bio-based eco-friendly composite has the potential to be used as an aircraft interior component.

Aging Properties of Phenol-Formaldehyde Resin Modified by Bio-Oil Using UV Weathering

The aging properties of phenol-formaldehyde resin modified by bio-oil (BPF) were analyzed using ultraviolet (UV) weathering. The variations on bonding strength of BPF were measured, and the changes on microstructure, atomic composition and chemical structure of BPF were characterized by using a scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR), respectively. With the increase of aging time, the bonding strength decreased gradually, the resin surface became rougher and the O/C radio of resin surface increased. However, the loss rate of bonding strength of BPFs was 9.6⁻23.0% lower than that of phenol-formaldehyde resin (PF) after aging 960 h. The aging degree of BPF surfaces was smaller in comparison to PF at the same aging time. These results showed that the bio-oil had a positive effect on the anti-aging property. Analytical results revealed that with increasing the aging time, the XPS peak area of C⁻C/C⁻H decreased, while that of C=O and O⁻C=O increased. The intensity of methylene and ether bridges in NMR analysis decreased along with increasing the intensity of aldehydes, ketones, acids and esters. These results indicated that the aging mechanism of BPF was a process of the breakage of molecular chains and formation of oxygen-containing compounds.

Graphene/cardanol modified phenolic resin for the development of carbon fiber paper-based composites

Carbon fiber paper-based composites (GCPC) were prepared by impregnating carbon fiber papers in a solution of graphene and cardanol modified phenolic resin (GCP). GCP was characterized by thermal gravimetric analysis (TGA), and the electrical conductivity, mechanical properties, pore distribution, and porosity of GCPC were investigated by a four-probe tester, universal testing machine, microtopography, and porous material analyzer, respectively. The results show that the electrical properties and mechanical strength of GCPC were improved with the increase of graphene and cardanol content. The porosity decreased and the proportion of small holes increased with the increase of graphene, while the porosity increased and the proportion of small holes decreased with the increase of cardanol. When the content of cardanol was 20% (mass fraction), the tensile strength of the composite reached 38.17 MPa, the resistivity reached 18.46 mΩ cm, and the porosity reached 67.46%.

Carbon fiber paper-based composites (GCPC) were prepared by impregnating carbon fiber papers in a solution of graphene and cardanol modified phenolic resin (GCP).

Thermal behavior of phenolic-based ceramizable composites modified by nano-aluminum oxide

A novel ceramizable organic composite was prepared by compression molding using silicone-modified phenolic resin (PR) as the matrix, nano-aluminum oxide powder as the filler, glass powder with low melting point as the forming additive, and vitreous silica fiber as the reinforced material. The ablative characteristics were explored in terms of linear/mass ablation rate and microscopic pattern of ablation via the oxyacetylene torch tests. Thermal stability of the investigated composites was estimated by means of thermogravimetric analysis. The final charring yields after pyrolysis increased from 63% to 69% and 74%, respectively. The silicone-modified PR acted as cross-linking adhesive at low-temperature region and tended to convert to bonding layer at high-temperature region. The formation and growth of the ceramic phase after thermal treatment enhanced the thermal stability and ablation performance of the composites at high-temperature region. The morphology and phase composition of the residual chars were studied by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction, respectively. The test results revealed that the modified composite possessed excellent thermal stability and ablation property.

Bio-Based Polymers with Potential for Biodegradability

A variety of renewable starting materials, such as sugars and polysaccharides, vegetable oils, lignin, pine resin derivatives, and proteins, have so far been investigated for the preparation of bio-based polymers. Among the various sources of bio-based feedstock, vegetable oils are one of the most widely used starting materials in the polymer industry due to their easy availability, low toxicity, and relative low cost. Another bio-based plastic of great interest is poly(lactic acid) (PLA), widely used in multiple commercial applications nowadays. There is an intrinsic expectation that bio-based polymers are also biodegradable, but in reality there is no guarantee that polymers prepared from biorenewable feedstock exhibit significant or relevant biodegradability. Biodegradability studies are therefore crucial in order to assess the long-term environmental impact of such materials. This review presents a brief overview of the different classes of bio-based polymers, with a strong focus on vegetable oil-derived resins and PLA. An entire section is dedicated to a discussion of the literature addressing the biodegradability of bio-based polymers.

Novel cardanol-containing boron-modified phenolic resin composites

To improve the thermal stability of phenolic resin and develop functional sustainable adhesive, a thermal-resistant cardanol-containing boron–phenolic resin (CBPR) was prepared by copolymerizing salicyl alcohol, cardanol, and boric acid. The structure of CBPR was characterized by Fourier transform infrared spectroscopy. Thermal stability of the investigated composites was estimated using thermogravimetric analysis (TGA). The results of TGA indicated that the modified resin exhibited excellent thermal stability. Specifically, the B-0.2 thermoset had a char yield of 69% when the boron content was only 1.27 wt%. The curing kinetic behavior was well described by differential scanning calorimetry and model-free kinetic analysis. Further, CBPRs, nano-aluminum oxide powders, glass powders with low melting point, and vitreous silica fibers were used as resin matrix, filler, forming additive, and reinforced material, respectively, to produce a novel ceramizable phenolic molding composite. The ablative characteristics of the co-cured blends were explored in terms of linear/mass ablation rate and microscopic pattern of ablation via the oxyacetylene torch tests. After thermal treatment, the formation and growth of the ceramic phase enhanced the thermal stability and ablation performance of the composites at high-temperature region. The morphology and phase composition of the residual chars were studied by scanning electron microscopy and energy dispersive spectroscopy, respectively. The linear and mass ablation rates for the modified composites decreased obviously in comparison with those of the unmodified composites, indicating that the modified composites possessed enhanced thermal stability and ablation property.

Microwave-assisted synthesis and characterization of resole-type phenolic resins

Resoles were prepared under microwave irradiation with different phenols, such as phenol, o-, p-, and m-cresols, separately with formaldehyde having formaldehyde/phenol ratio of 2:1 in basic medium. Analogical synthesis was performed using conventional heating for comparing the methods. The methylolation of phenol was confirmed by Fourier transform infrared spectroscopic analysis and a reaction mechanism was proposed. The number-average molecular weight was found by gel permeation chromatography technique. On the basis of the calculated value of kinetic chain length, the structure of the resole-type phenolic resin was proposed. Differential scanning calorimetry technique was used to investigate the curing behavior. As assessed by dynamic thermogravimetry, traces of resole sample prepared from p-cresol were found to possess better thermal stability, both in conventional as well as microwave-irradiated systems, among all other resole samples. The tensile strength, elongation at break, and impact strength showed an increasing trend. The main advantage of the process is about sixfold reduction of reaction time of the process carried at microwave reactors in comparison with the conventional heating.

The Preparation and Performance of Phenolic Foams Modified by Active Polypropylene Glycol

A series of active polypropylene glycols (APPGs) were synthesized by the reaction of hexamethylene-1,6-diisocyanate (HDI) and polypropylene glycol (PPG). They were then mixed and reacted with resol resin in catalyst condition to prepare the phenolic foams. The structure of modified phenolic foams was investigated. The influence of Mn of PPG and proportion of APPG on mechanical and fire-retardant performances of foams was discussed. The research results showed that the flexible PPG can be inducted into the crosslink structure of phenolic foam by the together crosslink reaction of –NCO groups in APPG with –CH2–OH groups in resol resin. When the molecular weight of PPG was 2000 and the dosage of APPG was 15% the max strain increased by 87%, mass loss (friability) decreased by 52%, thermal conductivity decrease from 0.033 to 0.028 W/(m·K), meanwhile the LOI can maintain above 30.

Synthesis, characterization and anti-microbial activity of phenylurea-formaldehyde resin (PUF) and its polymer metal complexes (PUF-Mn(II)

Phenylurea-formaldehyde polymer (PUF) was synthesized via polycondensation of phenylurea and formaldehyde in basic medium, its polymer-metal complexes [PUF-M(II)] were prepared with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) ions. PUF and PUF-M(II) were characterized with magnetic moment measurements, elemental and spectral (UV-visible, FTIR, 1H-NMR, 13C-NMR and ESR) analysis. The thermal behaviors of all the synthesized polymers were carried out using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The thermal data revealed that all of the PUF-M(II) showed higher thermal stabilities than the PUF and also ascribed that the PUF-Cu(II) showed better thermal stability than the other PUF-M(II). The kinetic parameters such as activation energy, pre-exponential factor etc., were evaluated for these polymer metal complexes using Coats-Redfern equation. In addition, the antimicrobial activity of the synthesized polymers was tested against several microorganisms using agar well diffusion methods. Among all of the PUF-M(II), the antimicrobial activity of the PUF-Cu(II) showed the highest zone of inhibition because of its higher stability constant and may be used in biomedical applications.