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Open AccessArticle

Green Processes for Green Products: The Use of Supercritical CO₂ as Green Solvent for Compatibilized Polymer Blends

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Polymers 2018, 10(11), 1285; https://doi.org/10.3390/polym10111285 - 19 Nov 2018

Cited by 10 | Viewed by 3761

Abstract

Polycaprolactone-g-glycidyl methacrylate (PCL-g-GMA), a reactive interfacial agent for PCL-starch blends, is synthesized using supercritical carbon dioxide (scCO₂) as reaction medium and relatively high molecular weight PCL (M_w = 50,000). Higher GMA and radical initiator intakes [...] Read more.

Polycaprolactone-g-glycidyl methacrylate (PCL-g-GMA), a reactive interfacial agent for PCL-starch blends, is synthesized using supercritical carbon dioxide (scCO₂) as reaction medium and relatively high molecular weight PCL (M_w = 50,000). Higher GMA and radical initiator intakes lead to higher functionalization degrees (FD) for PCL-g-GMA samples. A mathematical model is developed to describe the correlation between monomer and initiator intake and FD values. The model shows an excellent R²-value (0.978), which implies a good fit of the experimental data. Comparison of this model with a similar one for the reaction in the melt clearly indicates a better reaction efficiency in scCO₂. Furthermore, GPC results show that less degradation occurred for samples made in scCO₂. Finally, the use of the PCL-g-GMA made in scCO₂ (as interfacial agent) in ternary blend of PCL/starch/PCL-g-GMA results in better mechanical properties with respect to those obtained by using the same graft-copolymer as prepared in the melt. Full article

(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)

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Open AccessArticle

Synthesis of Linseed Oil-Based Waterborne Urethane Oil Wood Coatings

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Chia-Wei Chang

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Jing-Ping Chang

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Kun-Tsung Lu

Polymers 2018, 10(11), 1235; https://doi.org/10.3390/polym10111235 - 07 Nov 2018

Cited by 11 | Viewed by 4126

Abstract

The linseed oil glyceride (LOG) was synthesized by using a transesterification process with a glycerol/linseed oil molar ratio of 1.0. The waterborne urethane oil (WUO) wood coating was prepared by acetone process. First, dimethylolpropionic acid was reacted with hexamethylene diisocyanate (HDI) or isophorone [...] Read more.

The linseed oil glyceride (LOG) was synthesized by using a transesterification process with a glycerol/linseed oil molar ratio of 1.0. The waterborne urethane oil (WUO) wood coating was prepared by acetone process. First, dimethylolpropionic acid was reacted with hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI), followed by adding LOG at various NCO/OH molars of 0.7, 0.8, and 0.9, respectively, and the COOH-containing prepolymer was obtained. Then, the ionomer which was prepared by neutralizing prepolymer with trimethylamine, was dispersed by adding deionized water, and the water–acetone dispersion was obtained. Finally, the acetone was removed by vacuum distillation. In the whole synthesized process, the LOG and COOH-containing prepolymer could be steadily synthesized by FTIR analysis, and the weight-average molecular weight and polydispersity of COOH-containing prepolymer increased with an increase of NCO/OH molar ratios. During the water dispersion process of the ionomer acetone solution, the point of phase inversion was prolonged, meaning the solid content decreased with an increase of NCO/OH molar ratios. After acetone was removed, the color of WUO was milky-white, and it was weakly alkaline and possessed a pseudoplastic fluid behavior. The particle size of WUO increased with increasing of NCO/OH molar ratios, however, the storage stability was extended for HDI and shortened for IPDI synthesized with increasing of NCO/OH molar ratios. Full article

(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)

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Open AccessArticle

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

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Polymers 2018, 10(11), 1183; https://doi.org/10.3390/polym10111183 - 24 Oct 2018

Cited by 12 | Viewed by 4000

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)

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Open AccessArticle

Diels–Alder-Crosslinked Polymers Derived from Jatropha Oil

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Muhammad Iqbal

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Remco Arjen Knigge

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Hero Jan Heeres

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Antonius A. Broekhuis

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Francesco Picchioni

Polymers 2018, 10(10), 1177; https://doi.org/10.3390/polym10101177 - 22 Oct 2018

Cited by 6 | Viewed by 4205

Abstract

Methyl oleate, methyl linoleate, and jatropha oil were fully epoxidized using in situ-generated performic acid. The epoxidized compounds were further reacted with furfurylamine in a solvent-free reaction to obtain furan-functionalized fatty esters which, then, functioned as oligomers for a network preparation. Thermoreversible crosslinking [...] Read more.

Methyl oleate, methyl linoleate, and jatropha oil were fully epoxidized using in situ-generated performic acid. The epoxidized compounds were further reacted with furfurylamine in a solvent-free reaction to obtain furan-functionalized fatty esters which, then, functioned as oligomers for a network preparation. Thermoreversible crosslinking was obtained through a (retro) Diels–Alder reaction with bismaleimide, resulting in the formation of a brittle network for furan-functionalized methyl linoleate and jatropha oil. The furan-functionalized fatty esters were mixed with alternating (1,4)-polyketone reacted with furfurylamine (PK-Furan) for testing the mechanical and self-healing properties with DMTA and DSC, respectively. Full self-healing properties were found, and faster thermoreversibility kinetics were observed, compared to PK-Furan. Full article

(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)

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Open AccessArticle

Lignin Phenol Formaldehyde Resoles Using Base-Catalysed Depolymerized Kraft Lignin

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Pia Solt

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Björn Rößiger

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Johannes Konnerth

and Hendrikus W. G. Van Herwijnen

Polymers 2018, 10(10), 1162; https://doi.org/10.3390/polym10101162 - 17 Oct 2018

Cited by 34 | Viewed by 10059

Abstract

Lignin phenol formaldehyde (LPF) resols were produced using depolymerized lignin fractions at various levels of phenol substitution (50 to 70 wt %). To produce monomeric-rich (BCD-oil) and oligomeric (BCD-oligomers) bio-based phenolic compounds, softwood kraft lignin was base-catalysed degraded. These base-catalysed depolymerized (BCD) building [...] Read more.

Lignin phenol formaldehyde (LPF) resols were produced using depolymerized lignin fractions at various levels of phenol substitution (50 to 70 wt %). To produce monomeric-rich (BCD-oil) and oligomeric (BCD-oligomers) bio-based phenolic compounds, softwood kraft lignin was base-catalysed degraded. These base-catalysed depolymerized (BCD) building blocks were further used to substitute phenol in the synthesis of phenolic resins and were characterized in detail (such as viscosity, free formaldehyde and phenol content, chemical composition, curing and bonding behaviour). The adhesive properties were compared to a phenol formaldehyde (PF) reference resin and a LPF with untreated kraft lignin. The resins synthesized with the two depolymerized lignin types differ significantly from each other with increasing phenol substitution. While with LPF-BCD-oligomers the viscosity increases and the bonding strength is not effected by increasing lignin content in the resin, a reduction of these properties could be observed with LPF-BCD-oil. Furthermore, LPF-BCD-oil showed similar curing behaviour and ultimate strength as the reference LPF. Adhesive bonds made using LPF-BCD-oligomers exhibited similar strength to those made using PF. Compared to the reference resins, it has been demonstrated that modified renewable lignin based phenolic components can be an equally performing alternative to phenol even for high degrees of substitution of 70%. Full article

(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)

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Open AccessArticle

Improve the Performance of Soy Protein-Based Adhesives by a Polyurethane Elastomer

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Polymers 2018, 10(9), 1016; https://doi.org/10.3390/polym10091016 - 13 Sep 2018

Cited by 24 | Viewed by 4839

Abstract

The purpose of this study was to improve the performance of soy protein isolate (SPI) adhesives using a polyurethane elastomer. Triglycidylamine (TGA), SPI, thermoplastic polyurethane elastomer (TPU), and γ-(2,3-epoxypropoxy) propyltrimethoxysilane (KH-560) were used to develop a novel SPI-based adhesive. The residual rate, functional [...] Read more.

The purpose of this study was to improve the performance of soy protein isolate (SPI) adhesives using a polyurethane elastomer. Triglycidylamine (TGA), SPI, thermoplastic polyurethane elastomer (TPU), and γ-(2,3-epoxypropoxy) propyltrimethoxysilane (KH-560) were used to develop a novel SPI-based adhesive. The residual rate, functional groups, thermal stability, and fracture surface micrographs of the cured adhesives were characterized. Three-ply plywood was fabricated, and the dry/wet shear strength was determined. The experimental results suggested that introducing 2% TGA improved the residual rate of the SPI/TGA adhesive by 4.1% because of the chemical cross-linking reaction between epoxy groups and protein molecules. Incorporating 7% TPU into the SPI/TGA adhesive, the residual rate of the adhesive increased by 5.2% and the dry/wet shear strength of plywood bonded by SPI/TGA/TPU adhesive increased by 10.7%/67.7%, respectively, compared with that of SPI/TGA adhesive. When using KH-560 and TPU together, the residual rate of the adhesive improved by 0.9% compared with that of SPI/TGA/TPU adhesive. The dry and wet shear strength of the plywood bonded by the SPI/TGA/TPU/KG-560 adhesive further increased by 23.2% and 23.6% respectively when compared with that of SPI/TGA/TPU adhesive. TPU physically combined with the SPI/TGA adhesive to form a interpenetration network and KH-560 acted as a bridge to connect TPU and SPI/TGA to form a joined crosslinking network, which improved the thermo stability/toughness of the adhesive and created a uniform ductile fracture section of the adhesive. Full article

(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)

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Open AccessArticle

Effect of Selected Thiols on Cross-Linking of Acrylated Epoxidized Soybean Oil and Properties of Resulting Polymers

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Polymers 2018, 10(4), 439; https://doi.org/10.3390/polym10040439 - 14 Apr 2018

Cited by 20 | Viewed by 8819

Abstract

The effect of the chemical structure and functionality of three structurally different thiols on the cross-linking of acrylated epoxidized soybean oil and on the properties of the resulting polymers was investigated in this study. 1,3-Benzenedithiol, pentaerythritol tetra(3-mercaptopropionate), and an hexathiol synthesized from squalene [...] Read more.

The effect of the chemical structure and functionality of three structurally different thiols on the cross-linking of acrylated epoxidized soybean oil and on the properties of the resulting polymers was investigated in this study. 1,3-Benzenedithiol, pentaerythritol tetra(3-mercaptopropionate), and an hexathiol synthesized from squalene were used in the cross-linking of acrylated epoxidized soybean oil by thiol–Michael addition reaction. The reactivity of thiols determined from calorimetric curves followed the order: 1,3-benzenedithiol > pentaerythritol tetra(3-mercaptopropionate) > hexathiolated squalene. Thermal and mechanical properties and the swelling in different solvents of the cross-linked polymers were studied. The cross-linked polymer obtained from 1,3-benzenedithiol showed the highest swelling values in chloroform and toluene. The cross-linked polymer with pentaerythritol tetra(3-mercaptopropionate) fragments showed the best mechanical performance (highest mechanical strength and Young’s modulus) and thermal stability. The cross-linked polymers from hexathiolated squalene showed the highest glass transition temperature. Full article

(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)

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Open AccessArticle

Synthesis and Characterization of Wooden Magnetic Activated Carbon Fibers with Hierarchical Pore Structures

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Polymers 2018, 10(4), 435; https://doi.org/10.3390/polym10040435 - 13 Apr 2018

Cited by 5 | Viewed by 4141

Abstract

Wooden magnetic activated carbon fibers (WMACFs) with hierarchical pore structures were obtained by adding magnetic iron oxide (Fe₃O₄) nanoparticles into the liquefied wood. The structures and properties of WMACFs were analyzed by scanning electronmicroscopy (SEM), X-ray diffraction (XRD), Fourier [...] Read more.

Wooden magnetic activated carbon fibers (WMACFs) with hierarchical pore structures were obtained by adding magnetic iron oxide (Fe₃O₄) nanoparticles into the liquefied wood. The structures and properties of WMACFs were analyzed by scanning electronmicroscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption, and vibrating sample magnetometer (VSM). The results showed that WMACFs had high Brunauer-Emmett-Teller (BET) surface area (1578 m²/g) and total pore volume (0.929 cm³/g), of which 45% was the contribution of small mesopores of 2–3 nm. It is believed that Fe₃O₄ nanoparticles play an important role in the formation of hierarchical pores. With the Fe₃O₄ content increasing, the yield rate of WMACFs decreased, and the Fe₃O₄ crystal plane diffraction peaks and characteristic adsorption peaks were obviously observed. At the same time, it was also found that WMACFs had favorable magnetic properties when the Fe₃O₄ content was above 1.5%. As a result, WMACFs could be a promising candidate for high efficiency, low cost, and convenient separation for the magnetic field. Full article

(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)

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Open AccessArticle

Preparation and Characterization of Graphene Oxide-Modified Sapium sebiferum Oil-Based Polyurethane Composites with Improved Thermal and Mechanical Properties

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Polymers 2018, 10(2), 133; https://doi.org/10.3390/polym10020133 - 30 Jan 2018

Cited by 32 | Viewed by 5164

Abstract

Bio-based polyurethane (PU) composites with superior thermal and mechanical properties have received wide attention. This is due to the recent rapid developments in the PU industry. In the work reported here, novel nano-composites with graphene oxide (GO)-modified Sapium sebiferum oil (SSO)-based PU has [...] Read more.

Bio-based polyurethane (PU) composites with superior thermal and mechanical properties have received wide attention. This is due to the recent rapid developments in the PU industry. In the work reported here, novel nano-composites with graphene oxide (GO)-modified Sapium sebiferum oil (SSO)-based PU has been synthesized via in situ polymerization. GO, prepared using the improved Hummers method from natural graphene (NG), and SSO-based polyol with a hydroxyl value of 211 mg KOH/g, prepared by lipase hydrolysis, were used as raw materials. The microstructures and properties of GO and the nano-composites were both characterized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and tensile tests. The results showed that GO with its nano-sheet structure possessed a significant number of oxygen-containing functional groups at the surface. The nano-composites containing 1 wt % GO in the PU matrix (PU1) exhibited excellent comprehensive properties. Compared with those for pure PU, the glass transition temperature (T_g) and initial decomposition temperature (IDT) of the PU1 were enhanced by 14.1 and 31.8 °C, respectively. In addition, the tensile strength and Young’s modulus of the PU1 were also improved by 126% and 102%, respectively, compared to the pure PU. The significant improvement in both the thermal stability and mechanical properties for PU/GO composites was attributed to the homogeneous dispersion and good compatibility of GO with the PU matrix. The improvement in the properties upon the addition of GO may be attributable to the strong interfacial interaction between the reinforcing agent and the PU matrix. Full article

(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)

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Open AccessArticle

Styrene-Assisted Maleic Anhydride Grafted Poly(lactic acid) as an Effective Compatibilizer for Wood Flour/Poly(lactic acid) Bio-Composites

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Polymers 2017, 9(11), 623; https://doi.org/10.3390/polym9110623 - 15 Nov 2017

Cited by 22 | Viewed by 9400

Abstract

This study aimed to evaluate the effect of styrene-assisted maleic anhydride-grafted poly(lactic acid) (PLA-g-St/MAH) on the interfacial properties of wood flour/poly(lactic acid) (PLA) bio-composites. PLA-g-St/MAH was synthesized by free-radical melt grafting using styrene as a comonomer and dicumyl peroxide [...] Read more.

This study aimed to evaluate the effect of styrene-assisted maleic anhydride-grafted poly(lactic acid) (PLA-g-St/MAH) on the interfacial properties of wood flour/poly(lactic acid) (PLA) bio-composites. PLA-g-St/MAH was synthesized by free-radical melt grafting using styrene as a comonomer and dicumyl peroxide as an initiator. The structure of PLA-g-St/MAH was characterized by Fourier transform infrared spectroscopy. Wood flour/PLA composites were prepared by compression molding using PLA-g-St/MAH as a compatibilizer. The effects of PLA-g-St/MAH on the rheological and mechanical properties, as well as on the fractured surface morphology of the composites were investigated. Results indicated that storage modulus, complex viscosity, equilibrium torque, and shear heat were significantly increased. The mechanical properties of the wood flour/PLA composites were also significantly increased after the addition of PLA-g-St/MAH. The maximum values were achieved at the loading rate of 3 wt % because of the improved interfacial adhesion between the wood flour and the PLA matrix. Full article

(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)

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Open AccessArticle

Stereocomplexation, Thermal and Mechanical Properties of Conetworks Composed of Star-Shaped l-Lactide, d-Lactide and ε-Caprolactone Oligomers Utilizing Sugar Alcohols as Core Molecules

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Polymers 2017, 9(11), 582; https://doi.org/10.3390/polym9110582 - 06 Nov 2017

Cited by 8 | Viewed by 4858

Abstract

It is important to develop tailor-made biodegradable/biocompatible polymer networks usable for biomaterials whose thermal and mechanical properties are easily controlled by changing the composition. We synthesized sugar-alcohol-based polymer networks (SPN-mscLAO/3CLO, m = 4, 5 or 6) by the crosslinking reactions of [...] Read more.

It is important to develop tailor-made biodegradable/biocompatible polymer networks usable for biomaterials whose thermal and mechanical properties are easily controlled by changing the composition. We synthesized sugar-alcohol-based polymer networks (SPN-mscLAO/3CLO, m = 4, 5 or 6) by the crosslinking reactions of erythritol, xylitol or sorbitol-based m-armed star-shaped l-lactide and d-lactide oligomers (HmSLLAO and HmSDLAO), a glycerol-based 3-armed star-shaped ε-caprolactone oligomer (H3SCLO) and hexamethylene diisocyanate (HDI) at the weight ratios of HmSLLAO/HmSDLAO = 1/1 and (HmSLLAO + HmSDLAO)/H3CLO = 100/0, 75/25, 50/50, 25/75 or 0/100). The influence of the arm number on the crystallization behavior, thermal and mechanical properties of SPN-mscLAO/3CLOs were systematically investigated by comparing with those of sugar-alcohol-based homochiral polymer network (SPN-mLLAO, m = 4, 5 or 6) prepared by the reaction of HmSLLAO and HDI. Stereocomplex (sc) crystallites are dominantly formed for SPN-mscLAO/3CLOs 100/0–25/75, whereas SPN-mLLAOs were amorphous. The higher order of melting temperature of sc-crystals for SPN-mscLAO/3CLOs 100/0–25/75 was m = 5 > m = 6 > m = 4. The sc-crystallinities of SPN-4scLAO/3CLOs 100/0–50/50 were significantly lower than those of SPN-mscLAO/3CLOs 100/0–50/50 (m = 5 and 6). The larger order of the sc-spherulite size at crystallization temperature of 110 °C was m = 5 > m = 6 > m = 4 for SPN-mscLAO/3CLO 100/0. The size and number of sc-spherulites decreased with increasing crystallization temperature over the range of 110–140 °C and with increasing CLO fraction. Among all the networks, SPN-5scLAO/3CLOs 75/25 and 50/50 exhibited the highest and second highest tensile toughnesses (21.4 and 20.3 MJ·m⁻³), respectively. Full article

(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)

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Open AccessArticle

Fast Curing Bio-Based Phenolic Resins via Lignin Demethylated under Mild Reaction Condition

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Polymers 2017, 9(9), 428; https://doi.org/10.3390/polym9090428 - 07 Sep 2017

Cited by 65 | Viewed by 7715

Abstract

Demethylation technique has been used to enhance lignin reactivity for preparation of phenolic resins. However, the demethylation efficiency and the demethylated lignin (DL) reactivity were still unsatisfactory. To improve the demethylation efficiency, alkali lignin was demethylated under different mild conditions using sodium sulfite [...] Read more.

Demethylation technique has been used to enhance lignin reactivity for preparation of phenolic resins. However, the demethylation efficiency and the demethylated lignin (DL) reactivity were still unsatisfactory. To improve the demethylation efficiency, alkali lignin was demethylated under different mild conditions using sodium sulfite as a catalyst. Lignin and DL were characterized by ¹H-NMR (nuclear magnetic resonance) and Fourier transform infrared (FT-IR) spectroscopy to determine the demethylation mechanism. With the demethylation of lignin, the methoxyl group content decreased from 1.93 m mol/g to 1.09 m mol/g, and the phenolic hydroxyl group content increased from 0.56 m mol/g to 0.82 m mol/g. These results revealed that methoxyl groups were attacked by SO₃²⁻, and some methoxyl groups were converted to phenolic hydroxyl groups by a nucleophilic substitution reaction, generating DL with high reactivity. The chemical properties of lignin-based phenolic resins were studied by ¹³C-NMR and FT-IR spectroscopy, and their physical properties were also investigated. The results indicated that lignin-based phenolic resins exhibited faster curing rate and shorter gel time. In addition, the bonding strength increased from 0.92 MPa to 1.07 MPa, and the formaldehyde emission decreased from 0.58 mg/L to 0.22 mg/L after lignin demethylated at the optimum condition. Full article

(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)

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