Kinetics studies and characterization of poly(furfuryl alcohol) for use as bio‐based furan novolacs

Poly(furfuryl alcohol) (PFA) is an attractive target for the development of bio‐based novolac resins. However, control of the polycondensation reaction is not well understood and side reactions are an important factor for PFA and the development of new resins. The polymerization reactions and kinetics of furfuryl alcohol and 2‐furyl ethanol into polymeric resins are detailed in this work. Nuclear magnetic resonance spectroscopy analysis of reaction kinetics, molecular weight analysis, and rheology analysis confirm that the polymerization reaction rate of 2‐furyl ethanol is much faster than that of furfuryl alcohol because the addition of this methyl group serves to stabilize the carbocation transition state. Side reactions, such as Diels–Alder crosslinking and in particular branching, are quantified and were found to be much more prevalent in the polymerization of PFA. The glass transition temperature was measured to be 376 K for PFA and only 294 K for poly(2‐furyl ethanol). Molecular dynamics simulations showed that the alternative structure that forms in PFA that causes branching results in greater backbone rigidity causing its higher glass transition temperature. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46608.     

Synthesis and characterization of cetirizine‐containing,pH‐sensitive acrylic acid/poly(vinyl alcohol) hydrogels

In this study, interpenetrated acrylic acid (AA)/poly(vinyl alcohol) (PVA) hydrogels were prepared by free‐radical polymerization with N,N‐methylene bisacrylamide (MBAAm) as a crosslinker. The basic structural parameters, such as the molecular weight between crosslinks, volume interaction parameter, number of crosslinks, Flory–Huggins solvent interaction parameter, and diffusion coefficient, were calculated. Cetirizine dihydrochloride was loaded as a model drug in selected samples. The prepared hydrogels were evaluated for swelling, sol–gel fraction, and porosity. The swelling of the AA/PVA hydrogels was found to be directly proportional to the pH, that is, 1.2–7.5, depending on composition. The percentage of cetirizine hydrochloride was found to be directly proportional to the buffer pH and was at its maximum at pH 7.5, that is, 90–95%, and its lowest at pH 1.2, that is, 20–30%. The gel fraction increased with increasing concentration of AA and MBAAm, whereas the porosity showed the same response with AA, but an inverse relationship was observed with MBAAm. The drug‐release data were fitted into various kinetics models, including the zero‐order, first‐order, Higuchi, and Peppas models, which showed non‐Fickian diffusion. The prepared hydrogels were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, and no interaction was found among the polymer ratio and the drug. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43407.     

Thermochemical and isoconversional kinetic analysis of a polyester–epoxy hybrid powder coating resin for wood based panel finishing

Powder coating is an established technology especially for the surface finishing of metallic substrates for example in the automotive industry. Moreover, powder technology holds also great promises for the coating of non-conventional substrates like plastics or wood due to the lack of solvents and good recoverability. Here, low-temperature curing resins are required and especially mild processing conditions are demanded by the substrates. Advanced characterization methods need to be established that allow the precise balancing of the processing conditions required for adequate melting, flowing and curing of the powder with the process conditions that can be tolerated by the temperature-sensitive substrates. In the present contribution it is shown that differential scanning calorimetry (DSC) in combination with isoconversional kinetic analysis (ICKA) provides great potential for this purpose. DSC is a standard thermo-chemical method that can be successfully used to study both the melting and curing processes of powder coatings and to determine, for example the glass transition temperature of the cured coating directly from the measured thermograms. However, still more information can be extracted from the enthalpy signals when more sophisticated methods of data post-treatment and analysis are employed. Isoconversional kinetic analysis techniques such as the Kissinger–Akahira–Sunose (KAS) or the advanced Vyazovkin (VA) approaches allow calculating the time-dependencies of physical and chemical processes at various temperatures based on the estimates of activation energies which are obtained from DSC raw data. These analyses allow for example to calculate the time required for a certain degree of cross-linking in the coating after processing the coating under specified curing conditions. In the present contribution the application of ICKA of DSC measurements for the analysis of the flowing and curing behaviour of a powder coating based on a polyester–epoxy hybrid resin is illustrated and the potential of this approach to predict optimal curing times for arbitrary curing temperatures is demonstrated. This is especially useful when temperature-sensitive substrates like wood-based panels are coated. Additionally, the potential to relate the thermo-chemical properties of the powder coating to the surface properties of the coated substrates is discussed.     

A study of mechanical properties of biobased epoxy network: Effect of addition of epoxidized soybean oil and poly(furfuryl alcohol)

A novel biobased thermoset interpenetrating network was introduced in this study. Epoxidized soybean oil (ESO) and poly(furfuryl alcohol) (PFA) were added to a commercial biobased epoxy resin. It was hypothesized that addition of ESO and PFA can decrease brittleness of bioepoxy resin and also increase biobased content. Mechanical properties of samples were evaluated using tensile and impact test. It was found that the addition of ESO and PFA increased notched Izod impact energy by 76.6%. This significant increase was related to incorporation of long flexible chains of ESO into the matrix. Hybridization of ESO and PFA in bioepoxy reduced tensile strength (around 70%), tensile modulus (around 90%), and glass transition temperature in comparison to neat bioepoxy. Tensile strength and modulus of hybridized system can be further improved by addition of natural fibers and the resultant composite may be considered as a good candidate for applications in which damping properties are important. Crosslink density was calculated using dynamic mechanical analysis and a decrease in crosslink density was observed in hybridized system. PFA domains were observed in the matrix using atomic force microscopy in peak force quantitative nano‐mechanical mode and it revealed inhomogeneity in the crosslinked structure. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44352.     

Isothermal and nonisothermal cure kinetics of an epoxy/poly(oxypropylene)diamine/octadecylammonium modified montmorillonite system

The effect of an octadecylammonium‐exchanged montmorillonite on the curing kinetics of a thermoset system based on a bisphenol A epoxy resin and a poly(oxypropylene)diamine curing agent were studied with differential scanning calorimetry (DSC) in isothermal and dynamic (constant‐heating‐rate) conditions. Montmorillonite and the prepared composites were characterized by X‐ray diffraction analysis and simultaneous DSC and thermogravimetric analysis. The analysis of the DSC data indicated that the intercalated octadecylammonium cations catalyzed the epoxy–amine polymerization. A kinetic model, arising from an autocatalyzed reaction mechanism, was applied to the DSC data. Fairly good agreement between the experimental data and the modeling data was obtained. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1765–1771, 2006     

Nonisothermal curing kinetics of epoxy resin composite utilizing Ga (III) xanthate as a latent catalyst

Cure kinetics and curing mechanism of epoxy resin composite utilizing gallium (III) xanthate as a latent catalyst was investigated and compared with the commercial latent catalyst UCAT3512T formulation. Nonisothermal differential scanning calorimetric technique at different heating rates was employed to investigate the kinetic parameters. Activation energy was determined using Kissinger's and Flynn‐Wall‐Ozawa methods. Ga (III) xanthate was found to possess superior latent properties compared with UCAT3512T since the activation energy value obtained was higher for epoxy resin composite consisting of Ga (III) xanthate than UCAT3512T. Friedman's isoconversional method was utlizied to for kinetic modeling. An autocatalytic model was found to be successful in describing the curing reaction for both of the formulations. The calculated conversion rate as a function of temperature obtained by solving the autocatalytic equation showed a very good fit with experimental values. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42149.     

Advanced anticorrosion coatings prepared from polybenzoxazine/siloxane-containing epoxy resin

In this study, a new type of coating comprising benzoxazine and siloxane-containing epoxy (SiEP) resin was prepared by the thermal curing method. The FTIR (Fourier transform infrared) analysis not only confirmed the complete reaction between polybenzoxaine and SiEP resin after heat curing, but also found the hydrogen-bonding interactions between them. The addition of SiEP resin significantly enhanced the hydrophobicity and adhesion ability of the coating and greatly improved the water contact angles of the blend coatings (>108°), compared to that of the pristine PBa coating, which attributed to the introduction of a Si O Si network structure in the matrix. In addition, the corrosion resistance of the coating was tested though a series of electrochemical experiment. According to the results, the corrosion current values of the blend coatings decreased by about four orders of magnitude compared to that of the pristine carbon steel, and the corrosion protection efficiency of the blend coatings were >99%, indicating good application prospect of these blend coatings.     

Controlled release of aspirin from pH‐sensitive chitosan/poly(vinyl alcohol) hydrogel

The aim of this study was to develop a cheap, pH‐sensitive enteric coating of aspirin with biocompatible polymers. A novel approach was used to develop enteric coating from chitosan (CS) and poly(vinyl alcohol) (PVA). Solutions of CS and PVA (5 : 1 mol ratio) were mixed and selectively crosslinked with tetraethoxysilane. IR analysis confirmed the presence of the incorporated components and the existence of siloxane linkages between CS and PVA. The crosslinking percentage and thermal stability increased with increasing amount of crosslinker. The response of the developed coating in different media, such as water, pH (nonbuffer and buffer), and ionic media showed hydrogel properties. All hydrogels showed low swelling in acidic and basic pH media, whereas maximum swelling was exhibited at neutral pH. This pH sensitivity of the hydrogel has been exploited as enteric coating for commercial aspirin tablets. The dissolution test of enteric‐coated aspirin tablet in simulated gastric fluid (pH 1.2) showed 7.11% aspirin release over a period of 2 h, whereas a sustained release of remaining aspirin (83.25%) was observed in simulated intestinal fluid (pH 6.8). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Coating of cotton yarn with poly(vinyl alcohol) and poly(N‐vinyl‐2‐pyrrolidone) crosslinked via ultraviolet radiation

The coating of cotton fiber is used in the textile industry to increase the mechanical resistance of the yarn and their resistance to vibration, friction, impact, and elongation, which are some of the forces to which the yarn is subjected during the weaving process. The main objective of this study was to investigate the use of synthetic hydrophilic polymers, poly(vinyl alcohol) (PVA), and poly(N‐vinyl‐2‐pyrrolidone) (PVP) to coat 100% cotton textile fiber, with the aim of giving the fiber temporary mechanical resistance. For the fixation of the polymer on the fiber, UV‐C radiation was used as the crosslinking process. The influence of the crosslinking process was determined through tensile testing of the coated fibers. The results indicated that UV‐C radiation increased the mechanical resistance of the yarn coated with PVP by up to 44% and the yarn coated with PVA by up to 67% compared with the pure cotton yarn, that is, without polymeric coating and crosslinking. This study is of great relevance, and it is important to consider that UV‐C radiation dispenses with the use of chemical substances and prevents the generation of toxic waste at the end of the process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Antifungal effect of carbendazim supported on poly(ethylene‐co‐vinyl alcohol) and epoxy resin

Ethylene‐vinyl alcohol copolymers (EVOH) were prepared by the conventional saponification of poly(ethylene‐co‐vinyl acetate) using a solution of potassium hydroxide in ethanol. An organic fungicide, consisting of a 2‐benzimidazole carbamoyl (CBZ) group supported on EVOH (EVOH‐CBZ), was prepared by the transesterification reaction of methyl 2‐benzimidazole cabamate (carbendazim) with EVOH. The antifungal activity of the synthesized polymers was examined by the halo zone test against Aspergillus fumigatus and Penicillium pinophilum. The synthesized EVOH‐CBZ complex showed a strong antifungal activity. The bound CBZ units were susceptible to hydrolysis. CBZ bonded to an epoxy resin precursor, diglycidyl ether of bisphenol A (DGEBA‐CBZ), retained its antifungal activity, which was somewhat weaker in comparison with that of EVOH‐CBZ. When the DGEBA‐CBZ complex was crosslinked by isophoronediamine, the antifungal activity disappeared almost completely, indicating that it is necessary for the CBZ units to release from their polymer supports to have the antifungal effects. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 728–736, 2001     

Effect of furfuryl alcohol addition on the cure of furfuryl alcohol resin used in the glassy carbon manufacture

Glassy carbon can be manufactured practically without pores, named Monolithic Vitreous Carbon (MVC) or presenting up to 98% in transport pore volume, foam form, denominated Reticulated Vitreous Carbon (RVC). The glassy carbon processing is affected by some processing parameters, among them it can be cited the resin viscosity. The present work involves the optimization of RVC manufacture by monitoring the polyurethane (PU) foam impregnation with furfuryl alcohol resin with different viscosity values, which were obtained by dilution of the resin with different amounts of furfuryl alcohol. The resin samples used in the PU impregnation were characterized by thermal and rheological analyses. These results were correlated with scanning electron microscopy observations and compression test results of the impregnated polyurethane foam. The results show that the rheological behavior of the resin has significant influence on the polymerization step, affecting the homogeneity of impregnated foam and, consequently, its final properties, mainly the mechanical one. The impregnated foam prepared with the furfuryl alcohol resin diluted with 10% of furfuryl alcohol (η = 11.4 Pa s) showed higher compression values (0.26 MPa). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

A statistical approach to develop biocomposites from epoxy resin,poly(furfuryl alcohol), poly(propylene carbonate), and biochar

Epoxy composites are typically petroleum based and prone to fracture. Increasing concerns about climate change have motivated scientists to find green alternatives. To address both drawbacks, effect of addition of poly(propylene carbonate) polyol (PPC), a polyol derived from carbon dioxide, and biochar, a byproduct of pyrolysis in an epoxy/poly(furfuryl alcohol) (PFA) network was studied. It is hypothesized that addition of PPC will increase impact strength while addition of inexpensive biochar will offset cost of final product. In addition, incorporation of PFA, PPC, and biochar can increase biobased content of thermoset. A statistical approach was used to find a systematic correlation between constituent contents and mechanical properties of biocomposites. Mixture design of experiment and backward elimination regression were used to model mechanical properties of biocomposites. The fitted models showed a great ability to predict mechanical properties of new formulations. Addition of 10% biochar increased tensile strength and toughness by 13% and 34%, respectively. Biochar also increased modulus while it had adverse effect on impact strength. Promising effect of PPC on toughening of matrix was proved and it was found that addition of 30% of PPC increased impact strength by fivefolds. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45307.     

Amino‐capped aniline trimer/epoxy resin intercrosslinked networks

An amino‐capped aniline trimer (ACAT) in emeraldine base form was reacted with an epoxy resin to produce intercrosslinked networks. The quinoid structure of the ACAT was able to crosslink on curing and, thus, led to a very high glass‐transition temperature of the cured resin. The epoxy resin cured with the ACAT showed superior thermal properties over the resins cured with p‐phenylenediamine and 4,4′‐diamino diphenylamine. These findings were based on differential scanning calorimetry, IR, dynamic mechanical analysis, and thermogravimetric analysis data. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 222–226, 2006     

Toward poly(furfuryl alcohol) applications diversification: Novel self‐healing network and toughening epoxy–novolac resin

Poly(furfuryl alcohol) bioresin (PFA) was synthesized and utilized through two distinct alloying strategies. It was crosslinked by a bismaleimide (BMI) via a Diels–Alder (DA) reaction. The novel PFA–BMI polyadduct network was spectrally, thermally, and thermo‐mechanically characterized and its thermally repeatable self‐healing behavior was visually established. The network showed a high pyrolytic thermostability (char yield ∼51% at 600 °C). PFA was also used for modification of epoxy–novolac resin (EP). EP hybrid resins containing 5, 10, and 15 wt % of PFA were cured by a polyamine hardener. Despite of different curing mechanisms of the two resins, PFA had no effect on EP curing behavior as revealed by differential scanning calorimetry, which proved homogeneous formation of the thermosets. PFA at the composition of 15 wt % improved tensile properties and toughness of EP, so that it almost doubled tensile modulus and elongation at break. However, PFA slightly deteriorated flexural properties of EP. PFA also decreased T_g of EP, with a maximum decrease of 22 °C. Besides, PFA disfavored initial thermostability of EP, but improved its pyrolytic char yield. In conclusion, PFA can be beneficial from smart materials to toughen hybrid epoxy thermosets with potential applications in composites, adhesives, and surface coatings. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45921.     

Properties of chitosan/poly(vinyl alcohol) films for drug‐controlled release

With bovine serum albumin (BSA) as a model drug, drug‐loaded films of chitosan (CS) and poly(vinyl alcohol) (PVA) were obtained by a casting/solvent evaporation method and crosslinked by tripolyphosphate (TPP). The films were characterized by FTIR, XRD, and SEM. The influential factors of drug‐loaded films on drug‐controlled release were studied. These factors included, primarily, the component ratio of CS and PVA, the loaded amount of BSA, the pH and ionic strength of the release solution, and the crosslinking time with TPP. The results showed that within 25 h, when the weight ratios of CS to PVA in the drug‐loaded films were 90 : 10, 70 : 30, 50 : 50, and 30 : 50, the cumulative release rates of BSA were 63.3, 72.9, 81.8, and 91.8%, respectively; when the amounts of model drug were 0.1, 0.2, and 0.3 g, the release rates were 100, 81.8, and 59.6%, respectively; when the pH values of the drug release medium were 1.0, 3.8, 5.4, and 7.4, the release rates reached 100, 100, 37.9, and 7.8%, respectively; the cumulative release rates of BSA were 78.4, 82.3, 84.3, and 91.7% when the ionic strengths of the release solution were, respectively, 0.1, 0.2, 0.3, and 0.4M; when the crosslinking times of these drug films in the TPP solution were 0, 5, 15, 30, and 60 min, the release rates attained 100, 100, 81.8, 65, and 43.3%, respectively. All the results indicated that the CS/PVA film was useful in drug delivery systems. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 808–813, 2005     

Silica/poly(styrene-alt-maleic anhydride) hybrid particles as a reactive toughener for epoxy resin

Amino-modified silica nanoparticles (SiO₂─NH₂) were first prepared by hydrolytic condensation of tetraethyl orthosilicate and 3-aminopropylmethyldiethoxysilane. Then, organic–inorganic hybrid particles (SiO₂─SMA) were prepared by the amidation reaction between SiO₂─NH₂ and poly(styrene-alt-maleic anhydride) (SMA). Subsequently, SiO₂─SMA particles were employed for modifying bisphenol-A epoxy/anhydride thermoset. Compared with pure cured epoxy, the modified epoxy thermosets with only 1 wt % of SiO₂─SMA particles could achieve a simultaneous toughening and reinforcing performance. The tensile strength, impact strength, and fracture toughness of epoxy thermoset were increased by 14.1, 44.3, and 114.4%, respectively. Moreover, the modification also improved the thermal stability of epoxy thermosets, and the modulus and glass transition temperature of cured resin were not sacrificed. It can be attributed to the rigid structure of SiO₂, as well as the anhydride and carboxyl groups onto the surface of SiO₂─SMA particles participating in the epoxy curing reaction and effectively enhancing the crosslinking density of epoxy thermoset.     

丁香酚环氧有机硅树脂的制备及其固化动力学研究

利用丁香酚环氧和环四硅氧烷硅氢加成得到新型生物基环氧树脂D4EUEP,通过核磁共振氢谱和飞行时间质谱表征其准确结构。使用非等温DSC对D4EUEP/33DDS固化体系进行分析,采用双参数自催化模型和Málek判据建立了该体系固化动力学模型。模型计算结果与实验结果相关系数大于99%,证明该模型可以较好地描述D4EUEP/33DDS体系的固化过程。通过AICM方法研究了体系的有效活化能与转化率之间的关系,揭示了微观反应机理的变化,并通过Vyazovkin法对D4EUEP/33DDS体系进行了等温固化预测。     

Curing of poly(furfuryl alcohol) resin catalyzed by a homologous series of dicarboxylic acid catalysts: Kinetics and pot life

Curing kinetics and pot life are two vital characteristics for the application of poly(furfuryl alcohol) (PFA) resin because of the complexities both in the resin composition and curing mechanisms involved. However, few reports have provided a complete picture of PFA curing behavior. In this research, the effect of the addition of catalysts on the pot life and curing behavior of a PFA resin were evaluated. A homologous series of dicarboxylic acids [i.e., oxalic acid (OX), succinic acid (SU), and adipic acid (SA)] were used as the catalysts. Rheometric and nonisothermal differential scanning calorimetry (DSC) measurements and headspace gas chromatography/mass spectrometry analysis were carried out at 0, 6, and 24 h after the addition of the catalyst. The relaxation exponent (n), gel stiffness (S), and gel strength (A_F) of the prepared compositions were calculated with the Winter and Chambon and Gabriele rheological models. Furthermore, the curing kinetics were evaluated by the fitting of nonisothermal, multiple‐heating‐rate models. The DSC measurements showed a higher curing degree for samples containing OX catalyst compared to their counterparts containing either SU or AD. The rheometric findings supported an increased stiffness, gel strength, and curing development of the resin in the presence of OX compared to samples containing SU or AD. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44009.     

A logistic kinetic model for isothermal and nonisothermal cure reactions of thermosetting polymers

A model describing the low‐temperature crystallization kinetics observed for thermoplastic polymers from the melt by differential scanning calorimetry (DSC) was shown to accurately predict the cooling curves as a function of time and temperature. The model was successful for treating data for several cooling rates as well as for isothermal DSC data. In this article, we extended the model to cure reactions of thermosetting polymers. The parameters representing lower and upper exotherm reference temperatures in crystallization events have a different meaning for curing events. Thus, the model was modified to account for this change of context. The new model was tested for exothermic reactions of a Hysol® FP4527 epoxy adhesive system using data from DSC ramp heating experiments at several heating rates and also from isothermal experiments. Good fits were obtained for all the varied experimental conditions. The model made use of three fitting parameters with physical significance: a lower critical temperature (T_c) an activation energy (E_b), and a reaction order (τ + 1). Additionally, to complete the kinetic fitting, the dependence of the time to reach the reaction peak maximum for isothermal cure was considered. That dependence was found to follow a more simple model which is formally equivalent to that observed in isothermal crystallization, and which makes use of two parameters related to the limits of the temperature range in which the polymerization may occur. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40670.     

Curing of epoxy resin with poly(m‐phenylene methylphosphonate)

The mechanism and kinetics of curing of epoxy resin with poly(m‐phenylene methylphosphonate) (PMP) was studied by extraction and swelling experiments, DSC, ³¹P NMR, and FTIR. It was shown that at linear heating of 20°C/min PMP cures bisphenol A type epoxy resin at 230–300°C, whereas in the presence of catalytic amount of 2‐methyl imidazole the curing occurs at 200–230°C. Under isothermal conditions, epoxy resin was cured with PMP after 40–70 min at 150°C. An unusual mechanism of curing due to opening and insertion of epoxy into the phosphonate bond was suggested. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4011–4022, 2006