Bio-based Unsaturated Polyester Resins Research Articles

Life cycle assessment of an innovative bio-based unsaturated polyester resin and its use in glass fibre reinforced bio-composites produced by vacuum infusion

Oil-based polymeric resins are widely used in the manufacture of fibre-reinforced polymer (FRP) composites, contributing up to 70 % to their total weight. In an effort to reduce the dependence on oil-based feedstock, bio-based alternatives are being increasingly investigated. This study comprises a cradle-to-gate life cycle assessment (LCA) of a bio-based unsaturated polyester resin (UPR) and of glass-FRP (GFRP) composites produced with it using the vacuum infusion method. The bio-based unsaturated polyester prepolymer was developed by partially replacing oil-based chemical components with bio-based alternatives, namely fumaric acid, isosorbide, and 1,3-propanediol. Additionally, the use of the carcinogenic reactive diluent styrene was reduced by partial replacement (50 %) with 2-hydroxyethyl methacrylate. As benchmark, an oil-based UPR obtained from a typical formulation has been considered. The environmental profiles of resins, composites and of the production technique have been analysed to identify their relative contribution to the environmental burdens, which were estimated considering various impact categories. The LCA study revealed lower environmental impact from the bio-based UPR compared to its oil-based counterpart in most categories, namely climate change (total) (CCT, −75 %), ozone depletion (OD, −73 %), photochemical ozone formation (PCOF, −27 %), resource use (fossils) (RUF, −35 %), resource use (minerals and metals) (RUMM, −87 %), non-renewable primary energy (NRPE, −35 %); on the other hand, the conventional UPR was found to perform better in acidification (AC, −54 %), eutrophication (freshwater) (EFW, −55 %), eutrophication (terrestrial) (ET, −76 %), and renewable primary energy (RPE, −92 %) categories. Fumaric acid, isosorbide, and 1,3-propanediol used in the bio-based UPR were identified as the major contributors to impact categories. However, carbon sequestration from the production of 1,3-propanediol and fumaric acid together is responsible for a reduction of 54 % in the CCT indicator relative to considering the impacts from the net carbon emitting monomers alone. Similarly, the bio-UPR based GFRP composite has been found to perform better in CCT (−31 %), OD (−48 %), PCOF (−6 %), RUF (−17 %), RUMM (−10 %), and NRPE (−17 %), while the oil-based counterpart outperformed in AC (−26 %), EFW (−31 %), ET (−46 %), and RPE (−80 %). The single score of EN 15804:2012 + A2:2019 method reveals the better environmental performance of both bio-based UPR and its corresponding GFRP composite comparing to the conventional counterparts. These findings have the potential to support the selection, optimization, and design of more sustainable fibre-polymer composite materials for several industries, namely for structural applications in the construction sector.

Bio-based unsaturated polyester resin from post-consumer PET.

This study explores the utilization of post-consumer poly(ethylene terephthalate) (PET) as a material in the synthesis of styrene-free unsaturated polyester (UP) resin. The process involves glycolysis of PET waste with diethylene glycol and condensation polymerization with bio-based itaconic acid. The resulting unsaturated polyester possesses reactive methylidene functions that, in contrast to commonly employed fumarates/maleates, facilitate copolymerization with non-styrene reactive diluents. To formulate the resins, methacrylates and itaconates were used for dilution, and the curing process is achieved through a redox initiation system at room temperature, followed by post-curing at elevated temperatures. The cured formulations were characterized by their glass transition temperature, determined by DMA analysis. Mechanical properties were evaluated using standardized tests in tension, flexure, and compression. Particularly promising characteristics are observed in formulations incorporating bio-based dimethyl itaconate (DMI), allowing the formulation of materials with a high ultimate flexural strength (σf,max = 161.4 MPa) and compressive yield point (σc,yield = 131.3 MPa). Furthermore, the low volatility of DMI addresses the health, safety, and ecological concerns associated with the commonly used styrene. This technology not only presents a promising avenue for sustainable UP resin for glass fiber reinforced composites but also allows upcycling PET waste.

Novel Bio-based Branched Unsaturated Polyester Resins for High-Temperature Applications

AbstractUnsaturated polyester resins, one of the most important thermosets, are invariably produced from oil-based monomers. Their application is limited in areas where high thermal stability is required due to their low Tg. Besides, these resins contain 30–40% hazardous styrene as a reactive solvent. Therefore, developing bio-based solventless unsaturated polyester resin with medium to high thermomechanical properties compared to petrochemical-based counterparts is important. In order to achieve this, a series of branched bio-based unsaturated polyester resins were synthesized using bulk polymerization method in two steps. In the first step, four different intermediates were prepared by reacting glycerol (as a core molecule) with either isosorbide (diol), 1,3-propanediol (diol), 2,5-furandicarboxylic acid (saturated diacid), or adipic acid (saturated diacid). In the second step, the branched intermediate was end capped with methacrylic anhydride to introduce reactive sites for cross-linking on the branch ends. The chemical structure of the resins was characterized by 13C-NMR. FT-IR confirmed the polycondensation reaction in the first step and the end functionalization of the resins with methacrylic anhydride in the second step. The effect of 2,5-furandicarboxylic acid and isosorbide on thermomechanical and thermal properties was investigated using dynamic mechanical analysis, differential scanning calorimetry, and thermo-gravimetric analysis. Results indicated that 2,5-furandicarboxylic acid based resins had superior thermomechanical properties compared to a commercial reference unsaturated polyester resin, making them promising resins for high-temperature composite applications. For example, the resin based on 2,5-furandicarboxylic acid and isosorbide and the resin based on 2,5-furandicarboxylic acid and 1,3-propanediol gave glass transition temperatures of 173 °C and 148 °C, respectively. Although the synthesized 2,5-furandicarboxylic acid based resins had higher viscosity (22.7 Pas) than conventional unsaturated polyester (0.4–0.5 Pas) at room temperature, preheated resins can be used for making high-temperature-tolerance fiber-reinforced composite.

Synthesis, Characterization and Application of Biobased Unsaturated Polyester Resin Reinforced with Unmodified/Modified Biosilica Nanoparticles.

This paper presents sustainable technology for environmentally friendly composite production. Biobased unsaturated polyester resin (b-UPR), synthesized from waste polyethylene terephthalate (PET) glycosylate and renewable origin maleic anhydride (MAnh) and propylene glycol (PG), was reinforced with unmodified and vinyl-modified biosilica nanoparticles obtained from rice husk. The structural and morphological properties of the obtained particles, b-UPR, as well as composites, were characterized by Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The study of the influence of biosilica modification on the mechanical properties of composites was supported by hardness modeling. Improvement of the tensile strength of the b-UPR-based composite at 2.5 wt.% addition of biosilica modified with vinyl silane, named "b-UPR/SiO2-V" composite, has been achieved with 88% increase. The thermal aging process applied to the b-UPR/SiO2-V composite, which simulates use over the product's lifetime, leads to the deterioration of composites that were used as fillers in commercial unsaturated polyester resin (c-UPR). The grinded artificially aged b-UPR composites were used as filler in c-UPR for the production of a table top layer with outstanding mechanical properties, i.e., impact resistance and microhardness, as well as fire resistance rated in the V-0 category according to the UL-94 test. Developing sustainable composites that are chemically synthesized from renewable sources is important from the aspect of preserving the environment and existing resources as well as the extending their life cycle.

Freeze-Thaw Durability of Basalt Fibre Reinforced Bio-Based Unsaturated Polyester Composite.

This paper presents an experimental study of the wet freeze-thaw (FT) durability of a fibre-polymer composite produced by vacuum infusion using an innovative bio-based unsaturated polyester resin (UPR) and basalt fibres. As the benchmark, an equivalent composite produced with a conventional (oil-based) UPR was also tested. The composites were preconditioned in water immersion for 30 days at 20 °C followed by exposure to wet FT for up to 300 cycles; each FT cycle consisted of 3 h in dry freezing condition (-20 °C) and 8 h in thawing condition (23 °C) submerged in water. The composites' properties were assessed after preconditioning and after 100, 200, and 300 FT cycles, through mechanical (tensile, compressive, in-plane shear, interlaminar shear) and thermomechanical (dynamic mechanical analysis) tests. Gravimetric and scanning electron microscope analyses were also carried out. The results obtained show that the preconditioning stage, involving water immersion, caused most of the damage, with property reductions of 5% to 39% in the bio-composite, while in the oil-composite they ranged between 4% and 22%, being higher for matrix-dominated properties. On the other hand, FT alone had an insignificant effect on the degradation of material properties; after exposure to FT, property recovery was observed, specifically in matrix-dominated properties, such as interlaminar shear strength, which recovered by 12% in the bio-composite during exposure to FT. The overall performance of the bio-composite was inferior to the conventional one, especially during the preconditioning stage, and this was attributed to the hydrophilicity of some of the components of its bio-based resin.

Recent Advances on the Production of Itaconic Acid via the Fermentation and Metabolic Engineering

Itaconic acid (ITA) is one of the top 12 platform chemicals. The global ITA market is expanding due to the rising demand for bio-based unsaturated polyester resin and its non-toxic qualities. Although bioconversion using microbes is the main approach in the current industrial production of ITA, ecological production of bio-based ITA faces several issues due to: low production efficiency, the difficulty to employ inexpensive raw materials, and high manufacturing costs. As metabolic engineering advances, the engineering of microorganisms offers a novel strategy for the promotion of ITA bio-production. In this review, the most recent developments in the production of ITA through fermentation and metabolic engineering are compiled from a variety of perspectives, including the identification of the ITA synthesis pathway, the metabolic engineering of natural ITA producers, the design and construction of the ITA synthesis pathway in model chassis, and the creation, as well as application, of new metabolic engineering strategies in ITA production. The challenges encountered in the bio-production of ITA in microbial cell factories are discussed, and some suggestions for future study are also proposed, which it is hoped offers insightful views to promote the cost-efficient and sustainable industrial production of ITA.

GFRP biocomposites produced with a novel high-performance bio-based unsaturated polyester resin

This paper presents the manufacturing and the mechanical and thermomechanical properties of a bio-based glass fibre-reinforced polymer (GFRP) composite, produced by vacuum infusion, using an in-house high-performance bio-based unsaturated polyester resin (UPR) with more than 50 wt% of its content derived from renewable raw materials. Specimens were successfully produced, and their mechanical and thermomechanical properties was compared to an equivalent GFRP composite produced with conventional petroleum-based UPR and the same fibre architecture. The bio-based GFRP composite presented 538 MPa, 210 MPa, and 52 MPa of tensile, compressive, and shear strengths; 20 GPa, 24 GPa, and 2.5 GPa of tensile, compressive, and shear moduli; and 3.0%, 0.8%, and 14.8% of tensile, compressive, and shear strain at failure, meeting or exceeding the mechanical properties of the conventional counterpart. Furthermore, the bio-based GFRP composite presented a Tg of 64 °C (defined from onset of the storage modulus decay), enabling its outdoors use.

The Effect of Glycol Derivatives on the Properties of Bio-Based Unsaturated Polyesters.

The scope of the present study was to prepare fully bio-based unsaturated polyester resins (UPRs) with comparable properties to the commercial formulations. The focus was set on the determination of the optimal prepolymer formulation using the same set of diacids (itaconic and succinic acid) and different diols (propylene glycol, isosorbide and neopentyl glycol) or its equimolar mixtures, keeping the fixed molar ratio of 1:1:2.1 in all feed compositions. Instead of commonly used styrene, bio-based dimethyl itaconate was used as a reactive diluent (RD). The rheology of the obtained resins was studied in detail. The effect of the used diol on structural (FTIR), thermal (DSC), thermomechanical (DMA), and mechanical (tensile) properties was explained. The properties of UPRs were found to be highly dependent on the diol used in the prepolymer formulation. The UPR with an equimolar ratio of propylene glycol and neopentyl glycol was shown to be the most promising candidate to compete with the commercial petroleum-based resins.

Optimization of Reactive Diluent for Bio-Based Unsaturated Polyester Resin: A Rheological and Thermomechanical Study.

Nowadays, unsaturated polyester resins (UPR) are mainly obtained from non-renewable resources. The ever-increasing regulations and the continuous demand for more sustainability have led to extensive research towards more environmentally suitable alternatives to petroleum-based materials. However, one of the main disadvantages of bio-based UPR is their relatively high viscosity compared to petrochemical ones. In order to overcome this drawback, in this work, we investigated the possibility to lower the resin viscosity utilizing a mixture of dimethyl itaconate (DMI) and methyl methacrylate (MMA) as a reactive diluent. The effect of the DMI and MMA ratio on resin rheological properties was investigated. The optimal curing parameters were determined and all UPRs had a high gel content, which was shown to be dependent on the DMI and MMA ratio in the formulation. Furthermore, thermomechanical and mechanical properties of the resulting network were also found to be affected by the used reactive diluent mixture. A small substitution of DMI by MMA proved to be advantageous since it offers lower resin viscosity and improved mechanical properties.

Environmental Profile and Technological Validation of New High-Tg Unsaturated Polyesters from Fully Bio-Based Monomers and Reactive Diluents

This study was focused on the synthesis and characterization of a fully bio-based unsaturated polyester resin (UPR) with good thermal properties suitable for the commercial production of composite polymers. UPRs based on different ratios of bio-based furan dicarboxylic acid (FDCA), itaconic acid, and diols were synthesized. The unsaturated polymers prepared were evaluated by differential scanning calorimetry, gel permeation chromatography, FTIR and 1H-NMR spectroscopy. The results showed positive effects of FDCA on the glass transition temperature (Tg) of these fully bio-based polyesters, especially when FDCA was combined with 1,2-propanediol. Optimal values of Tg were obtained in the range of 30–32 °C for UPRs synthesized starting with a higher concentration of FDCA in the monomer feed. The possibility of substituting styrene, which usually acts as a reactive diluent, with a greener and safer alternative during the crosslinking of UPRs, was also explored. Two bio-based reactive diluents were considered: dimethyl itaconate (DMI) and butanediol dimethacrylate. After crosslinking, an average Tg of 75 °C and a good crosslinking efficiency indicated by a gel content of 90% were achieved for the fully bio-based polyester obtained under milder reaction conditions and dilution with DMI. Life cycle assessment was performed on selected UPRs, and comparison with a reference fossil-based resin in terms of the calculated category indicator results confirmed the lower environmental impact of the newly prepared bio-based polyesters.

Synthesis and characterization of high bio-based content unsaturated polyester resin for wood coating from itaconic acid: Effect of various reactive diluents as an alternative to styrene

The present work focuses on the ability of 2-hydroxyethyl methacrylate (HEMA), isobornyl methacrylate (IBOMA) and methyl methacrylate (MMA) as reactive diluents to replace styrene in unsaturated polyester resin based on itaconic acid, sebacic acid, 1,4-Butanediol, 1,6-Hexanediol and glycerol. The structural analysis confirmed the presence of itaconate linkages in the UPs. The synthesized resins were characterized by infrared spectroscopy and their physiochemical properties such as appearance, viscosity, acid value, %volatile content, curing characteristics like gel time, peak exotherm temperature and total cure time. Among all the resins formed; the resin based on 1,6-Hexanediol showed optimum molecular weight and viscosity needed for final application. The cured resins were investigated for their thermal stability by thermo-gravimetric analysis which revealed that all the diluted resins had good thermal stability. From the results it could be concluded that styrene-free bio-based unsaturated polyester resin can be synthesized having properties equivalent to the commercial styrene based resin.GRAPHICAL ABSTRACT

Composite materials from fully bio-based thermosetting resins and recycled waste poly(ethylene terephthalate)

During the last two decades, interest in bio-based polymers, especially in bio-based composite materials, has grown as a result of environmental concerns. In this paper new composites obtained from fully bio-based unsaturated polyester resin (UPR) and waste poly(ethylene terephthalate) (PET) were studied for the first time. The composites were prepared by crosslinking the UPR in the presence of functionalized PET particles (3, 6 and 9 wt%), using dimethyl itaconate as reactive diluent. The results showed that the incorporation of the PET particles led to the increase in mechanical properties. However, higher PET loading caused a decrease in the mechanical properties of the composites because of the PET particle agglomeration.

Catalyst Influence on Undesired Side Reactions in the Polycondensation of Fully Bio-Based Polyester Itaconates.

Bio-based unsaturated polyester resins derived from itaconic acid can be an alternative to established resins of this type in the field of radical-curing resins. However, one of the challenges of these polyester itaconates is the somewhat more elaborate synthetic process, especially under polycondensation conditions used on an industrial scale. The α,β-unsaturated double bond of the itaconic acid is prone to side reactions that can lead to the gelation of the polyester resin under standard conditions. This is especially true when bio-based diols such as 1,3-propanediol or 1,4-butanediol are used to obtain resins that are 100% derived from renewable resources. It was observed in earlier studies that high amounts of these aliphatic diols in the polyester lead to low conversion and gelation of the resins. In this work, a catalytic study using different diols was performed in order to elucidate the reasons for this behavior. It was shown that the choice of catalyst has a crucial influence on the side reactions occurring during the polycondensation reactions. In addition, the side reactions taking place were identified and suppressed. These results will allow for the synthesis of polyester itaconates on a larger scale, setting the stage for their industrial application.

Synthesis and characterization of fully bio-based unsaturated polyester resins

The sustainable tomorrow for future generations lies with the present industrial development toward the proper utilization of various bio-based products. For a transition to a higher level of sustainability, it is necessary to form a new platform for advanced technology products. This paper reports the development of new fully bio-based unsaturated polyesters resins (UPRs). A series of prepolymers were synthesized by varying saturated diacids (oxalic, succinic and adipic acid), itaconic acid and 1,2-propandiol. Dimethyl itaconate was used as a reactive diluent (RD) in amounts of 30, 35 and 40 wt%. Rheological measurements showed that the obtained resins possessed viscosities (234–2226 mPa s) amenable to a variety of liquid molding techniques. The impact of composition variables—prepolymer structure and amount of RD—on the chemical, mechanical and thermal properties of the thermosets was examined by DMA, TA and tensile measurements and was discussed in detail. The tensile properties (37–52 MPa), glass transition temperature (60–97 °C) and coefficient of thermal expansion (71–168 10−6 °C−1) of the cured resins were in the desired range for UPRs. This investigation showed that UPRs based on itaconic acid can be tailored during synthesis of the prepolymer to meet the needs of different property profiles.

Simple One-Pot Synthesis of Fully Biobased Unsaturated Polyester Resins Based on Itaconic Acid.

For the preparation of fully biobased unsaturated polyester resins (UPRs), the replacement of styrene with alternate nonpetroleum-based monomers turned out to be one of the most challenging tasks. Its complexity lies in the fact that reactive diluents (RD) have to have low viscosity and volatility, good compatibility with prepolymer, and capability to homopolymerize and copolymerize with its unsaturations. In this context, we directed our efforts to develop fully biobased UPRs using the dialkyl itaconates as an alternative to styrene. Therefore, a series of 100% biobased UPRs were prepared from itaconic acid and 1,2-propandiol and diluted by dialkyl itaconates. The resins were characterized by Fourier transform infrared spectroscopy, NMR, volatility, and viscosity measurements, while the cured samples were characterized by dynamic mechanical properties, thermomechanical analysis, thermogravimetric analysis data, and tensile tests. The influence of RD structure on the properties of cured samples was discussed in detail. It was shown that the prepared resins had evaporation rates of dialkyl itaconates of several orders of magnitude less compared to styrene. The cured resins with dimethyl itaconate showed comparable or even better thermal and mechanical properties compared to the one with styrene. This investigation showed that itaconic acid and dialkyl itaconates are promising bioresources for the preparation of fully biobased UPRs for mass consumption.

The impact of a designed lactic acid-based crosslinker in the thermochemical properties of unsaturated polyester resins/nanoprecipitated calcium carbonate composites

Unsaturated polyester composites (UPCs) were prepared from biobased unsaturated polyester resins (UPRs) and nanoprecipitated calcium carbonate (NPCC). The UPRs were obtained from the crosslinking reaction of an unsaturated polyester (UP) made from renewable monomers and styrene (St) or a mixture of St with a designed lactic acid-based crosslinker (BPPC). The UPCs were obtained by adding the NPCC to the formulations. Aspects of the composition of the UPs and of the BPPC were confirmed by FTIR and 1H NMR spectroscopies. Different UPCs were prepared and the influences of the addition of NPCC and of the amount of BPPC on their thermomechanical properties were evaluated. The BPPC has a major influence on the properties of the UPCs, namely a significant improvement of mechanical properties and of the thermal stability of UPCs. Both results suggest that the BPPC may be acting as a compatibilizer between the polymer matrix and the filler.

Synthesis of bio-based unsaturated polyester resins and their application in waterborne UV-curable coatings

In this paper, three bio-based unsaturated polyesters were synthesized from itaconic acid and different diols which could be derived from renewable resources. Their chemical structures were confirmed by FT-IR, 1H NMR and acid value as well as hydroxyl value. Waterborne UV curable networks based on these polyesters were manufactured and their mechanical properties, thermal stability and coating properties including pencil hardness, flexibility, adhesion, water resistance and solvent resistance were investigated. Results showed that the UV-cured polyester coatings exhibited high hardness, good water resistance and solvent resistance. The coatings reported in this paper combined the merits of bio-based materials, UV-curing process and water distribution.

Development of biobased unsaturated polyester resin containing highly functionalized castor oil

A highly functionalized castor oil product mainly composed of castor oil pentaerythritol glyceride maleates (COPERMA) was employed to fabricate a partial biobased unsaturated polyester resin (UPR) through blending it with petroleum-based UPR. The COPERMA product synthesized was characterized by FT-IR, 1H NMR, and ESI-MS to determine its possible structure and its functionality. The 1H NMR results showed that the maleate CC functionality of the COPERMA product was high (2.62). This highly functionalized product was then mixed with 35wt% styrene before blending this mix with petroleum-derived UPR to prepare a new partial biobased UPR. Physical, thermal, and mechanical properties of the UPR/COPERMA resins were carefully studied. Physical properties data indicate that the resultant biobased resins are suitable for liquid molding process and had a less shrinkage than the neat UPR. Compared to the neat UPR, the cured UPR/COPERMA resins demonstrated comparable or even better thermal and mechanical properties when the content of COPERMA resin was up to 10wt%. When the content of COPERMA resin increased to 20wt%, the tensile strength and storage modulus at 35°C decreased gradually, but not as much as reported in other oil/UPR systems, while other properties, such as crosslink density, glass transition temperature, tensile and flexural moduli, and impact strength, were still improved.

Determination of the Biobased Content in Plastics by Radiocarbon

Accelerator mass spectrometry (AMS) radiocarbon analyses were performed on biobased unsaturated polyester resins in order to assess the potential of the method for the determination of the bio-fraction. Different resins were synthesized in the laboratory with different proportions of raw materials of biogenic origin, and analyzed both in the liquid and in the solid form. As a preliminary step of the study, both the biobased and the fossil-derived raw materials were analyzed in order to determine their 14C content. A comparison of the obtained results with the expected ones allowed us to investigate the potential of the 14C method in this field as well as to address some still open issues such as the levels of uncertainty and accuracy as related to the calculation procedures, the correction for isotopic fractionation, and the effect of the presence of volatile components in the analyzed materials.

Thermal and Mechanical Properties of a Biobased Unsaturated Polyester Resin

Thermal and Mechanical Properties of a Biobased Unsaturated Polyester Resin