Thermoset Polyester Research Articles

Comparison of single- and hybrid-fiber composite laminates for use in prosthetic sockets

Traditional prosthetic sockets often consist of thermoplastic and wood-based materials. However, these sockets are known to be uncomfortable, heavy, and economically challenging. Natural fibers are quickly adapting and becoming more popular because of their biodegradable, long-lasting, and biocompatible nature. They are replacing synthetic fibers in the design and development of structural parts. This research looked into a new hybrid composite made of natural and synthetic fibers (basalt, jute, and carbon) that are reinforced in a polyester thermoset based matrix. The performance of this hybrid composite was then compared to that of pristine or single fiber-reinforced composites manufactured using woven jute, basalt, and carbon. The samples were manufactured using the vacuum-assisted resin transfer molding technique and cured at room temperature. The samples were then subjected to flexure and impact tests. The hybrid composite had an impact strength of 46.71 kJ/m2, higher than all other single fiber combinations. The flexural strength of the hybrid composite was determined to be 66.25 MPa, matching that of basalt fiber and surpassing that of other conventional single fiber composite laminates. Fractographic analysis has revealed that the main cause of failure in flexure is mostly attributed to delamination and fiber micro-buckling. Although hybrid reinforced composites had superior performance in terms of both impact and flexure strength, basalt fibers demonstrated comparable strength, specifically in flexure. Overall, the hybrid composite possesses exceptional promise for use in prosthetic construction.

Vinyl methyl oxazolidinone as reactive diluent to overcome the solubility limitations of highly polar unsaturated polyesters

AbstractVinyl methyl oxazolidinone (VMOX®) is studied as a new reactive diluent (RD) for highly polar unsaturated polyesters (UPs). Molecules with special structure properties are extensively investigated as components for unsaturated polyester resins (UPRs) and thermosets, particularly for high‐temperature applications. Special diols with a cyclic structure like isosorbide and tricyclodecanedimethanol or special diols with side groups like 2‐methyl‐2‐propyl‐1,3‐propanediol and 2‐ethyl‐2‐butyl‐1,3‐propanediol can provide interesting properties. Bio‐based diols such as isosorbide and 1,3‐butanediol improve the sustainability profile. However, UPs based on such special diols have a higher polarity, limiting their solubility in styrene. This demands a RD, which provides adequate solubility and is suitable for high‐temperature applications. Therefore, our study compares the solubility of highly polar UPs based on special diols in styrene and VMOX®. UPs with different formulations, polarities, and Hansen parameters were synthesized and characterized. The solubility sphere of styrene was determined experimentally with the synthesized UPs. The influence of the special diols on the thermoset properties was investigated in dynamic mechanical analysis measurements. In conclusion, VMOX® as a RD enables full utilization of special diols properties due to the wide solubility window. Moreover, a new class of high‐temperature styrene‐free UP resin was developed.

Itaconic Acid as a Comonomer in Betulin-Based Thermosets via Sequential and Bulk Preparation.

The inherent chemical functionalities of biobased monomers enable the production of renewably sourced polymers that further advance sustainable manufacturing. Itaconic acid (IA) is a nontoxic, commercially produced biobased monomer that can undergo both UV and thermal curing. Betulin is a biocompatible, structurally complex diol derived from birch tree bark that has been recently studied for materials with diverse applications. Here, betulin, IA, and biobased linear diacids, 1,12-dodecanedioic acid (C12) and 1,18-octadecanedioic acid (C18), were used to prepare thermosets using sequential and bulk curing methods. Thermoplastic polyester precursors were synthesized and formulated into polyester-methacrylate (PM) resins to produce sequential UV-curable thermosets. Bulk-cured polyester thermosets were prepared using a one-pot, solventless melt polycondensation using glycerol as a cross-linker. The structure-property relationships of the thermoplastic polyester precursors, sequentially prepared PM thermosets, and bulk-cured polyester thermosets were evaluated with varying IA content. Both types of thermosets exhibited higher storage moduli, Tgs, and thermal stabilities with greater IA comonomer content. These results demonstrate the viability of using IA as a comonomer to produce betulin-based thermosets each with tunable properties, expanding the scope of their applications and use in polymeric materials.

Sustainable and recyclable thermosets with performances for high technology sectors. An environmental friendly alternative to toxic derivatives

This study focuses on the development of environmentally friendly and chemically recyclable thermosets using or a renewable based monomer, the triglycidyl ether of phloroglucinol (TGPh), or a commercial non-toxic tris(4-hydroxyphenyl) methane triglycidyl ether (THPMTGE) monomer. The recyclable polyester thermosets were prepared by crosslinking the two monomers with hexahydro-4-methylphthalic anhydride (HMPA) or methyl nadic anhydride The TGPh-based formulations exhibited lower reaction temperatures and narrower reaction intervals. Additionally, these systems showed higher tan δ values (189°C–199°C), higher crosslinking densities (7.6–7.8 mmol cm−3) and compact networks, crucial for high-performance industries. Tensile tests demonstrated the remarkable mechanical properties of the thermosets, including high Young modulus (1.3–1.4 GPa), tensile stress (55–69 MPa), and an elongation at break around 3%–8%. Moreover, the thermosets exhibited complete dissolution at a temperature of 170°C, with depolymerization times of approximately 2.5 h for TGPh-based resins and 4.5 h for THPMTGE-based formulations. In conclusion, this study shows that sustainable and eco-friendly thermosets with excellent physico-chemical and thermo-mechanical properties, low hydrophilicity, and rapid dissolution capacity can be developed. These thermosets offer a viable alternative to non-recyclable and toxic resins in high-end industrial applications.

Polymer-Matrix Composites: Characterising the Impact of Environmental Factors on Their Lifetime.

Polymer-matrix composites are widely used in engineering applications. Yet, environmental factors impact their macroscale fatigue and creep performances significantly, owing to several mechanisms acting at the microstructure level. Herein, we analyse the effects of water uptake that are responsible for swelling and, over time and in enough quantity, for hydrolysis. Seawater, due to a combination of high salinity and pressures, low temperature and biotic media present, also contributes to the acceleration of fatigue and creep damage. Similarly, other liquid corrosive agents penetrate into cracks induced by cyclic loading and cause dissolution of the resin and breakage of interfacial bonds. UV radiation either increases the crosslinking density or scissions chains, embrittling the surface layer of a given matrix. Temperature cycles close to the glass transition damage the fibre-matrix interface, promoting microcracking and hindering fatigue and creep performance. The microbial and enzymatic degradation of biopolymers is also studied, with the former responsible for metabolising specific matrices and changing their microstructure and/or chemical composition. The impact of these environmental factors is detailed for epoxy, vinyl ester and polyester (thermoset); polypropylene, polyamide and poly etheretherketone (thermoplastic); and for poly lactic acid, thermoplastic starch and polyhydroxyalkanoates (biopolymers). Overall, the environmental factors mentioned hamper the fatigue and creep performances, altering the mechanical properties of the composite or causing stress concentrations through microcracks, promoting earlier failure. Future studies should focus on other matrices beyond epoxy as well as on the development of standardised testing methods.

On the electron beam-induced degradation of vinyl ester thermosets

We have demonstrated that electron beam radiolysis induces scissions of the C-O-C bonds along the backbone of the chains of unsaturated polyester thermosets of different compositions based on dicyclopentadiene, isophthalic acid, epoxy vinyl ester, and terephthalic acid. The radiolysis is imminent irrespective of the degree of crosslinking in the thermosets both in neat resins and in the presence of solvents. Electron Paramagnetic Resonance (EPR) results show the formation of the alkoxyl radicals and C-centered radicals as the primary intermediate products of the C-O-C scissions. While the alkoxyl radicals of these resins exhibit very good stability even six months after the irradiation, the C-centered radicals decay very rapidly via their reactions with oxygen that is available either as adsorbed in the resins, dissolved in solvents or from the environment. The radiolytically produced •OH radicals in the unsaturated-ester aqueous solutions play a major role in inducing scissions on the backbone of the polymer chains. The solvated electrons (es) from organic solvents, such as dimethyl sulfoxide and isopropyl alcohol, also induce direct scission of the C-O-C bonds, giving rise to the formation of alkoxyl radicals and C-centered radicals. However, a considerable fraction of es is scavenged by the dissolved O2 to produce O2−. Despite the radiation-induced scissions, irradiation of the resins at a dose level of 1000 kGy results in an increase of the glass transition temperature, Tg. This is due to the simultaneous radiation-induced polymerization of the vinyl monomers, toluene, and styrene that are present in the resins. The increase in Tg is observed in all the resins except for the terephthalic polyester resin in aqueous solution, in which the absence of these monomers results in Tg decreasing sharply with irradiation. This work demonstrates that ionizing radiation triggers continuous free radical-chain reactions that lead to the formation of recyclable oligomers.

Pultruded carbon fibre reinforced polymer strips produced with a novel bio-based thermoset polyester for structural strengthening

This paper presents the development and industrial manufacturing of a pultruded high-performance carbon fibre (CF) reinforced polymer (CFRP) composite strip using a bio-based unsaturated polyester (UP) resin containing more than 50% of its weight derived from renewable raw materials. The bio-based CF/UP strengthening strip, comprising unidirectional CF strands, was successfully produced and its mechanical and thermomechanical behaviours were assessed, and compared to an equivalent carbon fibre reinforced epoxy-vinyl ester (CF/VE) strip produced with conventional petroleum-based high-performance epoxy-vinyl ester resin and the same fibre architecture. The bio-based CF/UP composite strip presented 2095 MPa, 167 GPa, and 1.4% of tensile strength, modulus of elasticity, and strain at failure, respectively. These figures met or exceeded the mechanical properties of its equivalent conventional CF/VE counterpart tested under the same conditions. Furthermore, the bio-based CF/UP composite strip presented a glass transition temperature of 78 °C (defined from the onset of the storage modulus decay), enabling a maximum service temperature of ∼60 °C, which will not likely be exceeded in most climates, highlighting its potential for structural strengthening applications, and offering a key advantage in terms of sustainability.

Organocatalysis in ring opening copolymerization as a means of tailoring molecular weight dispersity and the subsequent impact on physical properties in 4D printable photopolymers

Organocatalysis for ring opening copolymerization was used to tailor molecular weight dispersity as a means of tailoring physical properties in 3D printed polyester thermosets made through thiol–ene crosslinking.

High performance, recyclable and sustainable by design natural polyphenol-based epoxy polyester thermosets

Development of high-performance materials with a high content of aromatic units and high functionality, using natural and renewable polyphenolic synthons such as naringenin and phloroglucinol.

Citric acid functionalized reduced graphene oxide containing bio‐based waterborne polyester thermoset as an excellent anticorrosive material

AbstractProtection of metal surfaces from corrosion by environmentally friendly coating is found to be an interesting and useful research topic. In this milieu, the authors presented an environment friendly bio‐based waterborne polyester thermoset as an anticorrosive organic coating. The polyesters comprise renewable resource based citric acid, dimer acid and glycerol along with citric acid functionalized reduced graphene oxide. Three different compositions of the polyester were produced by varying the amount (0.1, 0.5, and 1 weight%) of functionalized reduced graphene oxide. The structural and morphological attributes of these polyesters were evaluated by Fourier transform infrared spectroscopic, X‐ray diffraction, Raman spectroscopic, scanning electron microscopic, and transmission electron microscopic studies. The thermosets of the resinous polyesters were obtained by curing them with bio‐based glycerol containing epoxy and fatty acid modified poly(amido amine). The thermosets exhibited high tensile strength (18.68–26.94 MPa), elongation at break (176%–471%), toughness (22.74–86.5 MJ/m3), thermal stability (up to 222°C), biodegradability and chemical resistance. Potentiodynamic polarization and electrochemical impedance spectroscopic studies clearly revealed excellent corrosion resistance (impedance of the order of 107 ohm cm2 and highest phase angle of 88.2°) of the mild steel coated plates. Thus, the formulated polyester thermosets could be used as a promising environment friendly high performing anticorrosive material.

Identification of the fracture surface of thermoset polyester due to bending load

In this research, an attempt was made to improve the brittle nature of the Unsaturated Polyester (UP) polymer which cannot undergo plastic deformation to be improved to become more resilient by adding Thermoset Vinyl Ester and Methyl Methacrylate (MMA). To show the change in the toughness of the polyester material, a test is carried out to provide a tensile load and a flexural load until the material breaks This work reports the successful fabrication of polyester blends by mixing vinyl esters with different percentages. The test shows that there is a linear relationship between the shape of the fracture surface due to bending loads and observations through SEM which are directly related to the flexural stress properties with the fracture surface morphology. The mixture of polyester with 40% vinyl ester showed the highest flexural stress of 126.88 MPa while for pure polyester of 49.71 MPa this showed an increase of 255.24% compared to pure polyester. This shows that the addition of vinyl ester to polyester resulted in an increase in the toughness of the polyester, but for 100% vinyl ester the return stress decreased by 56.50 MPa. This indicates that due to the breaking of some of the polyester chain networks causes a decrease in the structural stiffness, which results in an increase in the plastic deformation zone fraction.

Development of high‐performance partially biobased thermoset polyester using renewable building blocks from isosorbide, 1,3‐propanediol, and fumaric acid

AbstractResearch on biobased thermoset resins has been overlooked when compared with the rapid progress on biobased thermoplastics. The objective of this work was to develop unsaturated polyester prepolymers based on building blocks derived from renewable raw materials, namely, biobased isosorbide, 1,3‐propanediol, and fumaric acid, with petroleum‐derived phthalic anhydride. The prepolymers developed herein behaved as low‐molecular weight macromolecules (oligoesters), with Mn varying between 1.2 and 1.5 kDa, but achieved a high bio‐content of up to 87.1 wt%. The prepolymers were incorporated into reactive diluents comprising a blend of 2‐hydroxyethyl methacrylate and styrene, formulated to be eco‐friendlier and less toxic than typical styrene‐only incorporation approach, thus resulting in resins with viscosities between 750 and 950 cP. These resins are suitable for use in various fiber‐reinforced polymer production techniques, such as manual lamination, vacuum infusion, and pultrusion, having the benefit of presenting over 50 wt% of bio‐content in some formulations. Moreover, the crosslinked polyester resins (thermosets) exhibit comparable mechanical and thermomechanical behavior to their petrochemical‐based counterparts, with modulus of elasticity and tensile strength of up to 3.9 GPa and 62.1 MPa, respectively, and glass transition temperatures of up to 106°C, making them greener alternatives for high‐performance structural applications.

Synthesis of polyester thermosets via internally catalyzed Michael-addition of methylene compounds on a 2-(trifluoromethyl)acrylate-derived building block

The Michael-addition reaction of methylene compounds has been known and used for>120 years in organic chemistry synthesis. We report herein a new type of application for this reaction: the preparation of thermosets by catalyst-free bis-Michael addition. In this study, the addition of various methylene C-nucleophiles on tert-butyl 2-(trifluoromethyl)acrylate in presence of a tertiary amine was preliminary evaluated. Then, a tris-2-(trifluoromethyl)acrylate monomer incorporating a tertiary amine was synthesized and used with methylene monomers to prepare innovative polyester networks at temperature going from 25 °C to 100 °C. Finally, the resulting fluorinated carbon-Michael networks were characterized by FTIR, differential scanning calorimetry, thermal gravimetry, dynamic mechanical and swelling analyses. These thermosets exhibited high gel content (>86 %) and good thermo-mechanical properties with a rubbery plateau above 7 MPa and a glass transition temperature above 44 °C. The material thermal properties could be adapted to a targeted application (binder or coating) by the choice of the methylene compound used in the thermoset formulation.

Low Formaldehyde Binders for Mineral Wool Insulation: A Review.

Insulating materials are ubiquitous in a built environment and play a critical role in reducing the energy consumed to maintain habitable indoor environments. Mineral wool insulation (MWI) products, including glass, stone, and slag variants, are the most widely used class of insulating materials in Europe and account for more than 50% of the total market by volume. MWI typically consists of two key components: a mesh of inorganic fibers that are several micrometers in diameter, and an organic thermosetting adhesive commonly referred to as the “binder.” Traditional phenol‐formaldehyde‐urea (PFU) binders used in the manufacture of MWI are increasingly being scrutinized for the formaldehyde released during their manufacture and service lifetime. The recent classification of formaldehyde as a carcinogen by various safety organizations has accelerated a paradigm shift within the industry toward alternative binder technologies that minimize or indeed eliminate formaldehyde emissions. This review examines more recent strategies for achieving low‐ or zero‐added formaldehyde binders for MWI, with a particular focus on the patent literature. The chemistry underpinning traditional PFU binders is presented and compared to new strategies involving scavenging molecules that decrease formaldehyde emissions, as well as zero‐added formaldehyde binder technologies such as polyester, Maillard, and epoxide thermosets.

A bio-based, robust and recyclable thermoset polyester elastomer by using an inverse vulcanised polysulfide as a crosslinker

We report the synthesis of a bio-based, robust and recyclable thermoset polyester elastomer by using an inverse vulcanised sulfur-polymer (SP) as a crosslinker for the bio-based polyester elastomer (BPE).

Implementation and Characterization of a Laminate Hybrid Composite Based on Palm Tree and Glass Fibers.

In this work, laminated polyester thermoset composites based on palm tree fibers extracted from palms leaflets and glass mats fibers were manufactured to develop hybrid compositions with good mechanical properties; the mixture of fibers was elaborated to not exceed 25 vol.%. Samples were prepared with a resin transfer molding (RTM) method and mechanically characterized using tensile and flexural, hardness, and impact tests, and ultrasonic waves as a non-destructive technique. The water sorption of these composite materials was carried out in addition to solar irradiation aging for approximately 300 days to predict the applicability and the long-term performance of the manufactured composites. Results have shown that the use of glass fibers significantly increased all properties; however, an optimum combination of the mixture could be interesting and could be developed with less glass sheet and more natural fibers, which is the goal of this study. On the other hand, exposure to natural sunlight deteriorated the mechanical resistance of the neat resin after only 60 days, while the composites kept high mechanical resistance for 365 days of exposure.

Comparison of two diphenyl polyenes as acid-sensitive additives during the biodegradation of a thermoset polyester polyurethane coating.

Biochemical hydrolysis and chemical catalysis are involved in the successful biodegradation of polymers. In order to evaluate the potential separation between biochemical and chemical catalysis during the biodegradation process, we report the use of two diphenylpolyenes (DPPs), all trans-1,4-diphenylbutadiene (DPB) and all trans-1,6-diphenylhexatriene (DPH), as potential acid-sensitive indicators in polymers. 1,4-Diphenylbutadiene and DPH (0.1% w/w) were melt-cast successfully with poly(ethylene succinate) hexamethylene (PES-HM) polyurethane (thermoset polyester polyurethane) coatings above 80℃. When these two DPP/PES-HM coatings were exposed to a concentrated supernatant with significant esterase activity resulting from the growth of a recently isolated and identified strain of Tremellomycetes yeast (Naganishia albida 5307AI), the DPB coatings exhibited a measurable and reproducible localized decrease in the blue fluorescence emission in regions below where hydrolytic biodegradation was initiated in contrast with DPH blended coatings. The fluorescence changes observed in the biodegraded DPB coating were similar to exposing them to concentrated acids and not bases. Our experiments resulted in (1) a method to blend DPP additives into thermoset coatings, (2) the first report of the biodegradation of polyester polyurethane coating by N.albida, and (3) demonstration that hydrolytic supernatants from this strain generate acidic region within degrading polyester coatings using DPB as the indicator. Our experiments confirm that N.albida is an active polyester degrader and that DPB is a promising acid sensitive polymer coating additive.

Co-Bonded Hybrid Thermoplastic-Thermoset Composite Interphase: Process-Microstructure-Property Correlation.

Co-bonding is an effective joining method for fiber-reinforced composites in which a prefabricated part bonds with a thermoset resin during the curing process. Manufacturing of co-bonded thermoset-thermoplastic hybrid composites is a challenging task due to the complexities of the interdiffusion of reactive thermoset resin and thermoplastic polymer at the interface between two plies. Herein, the interphase properties of co-bonded acrylonitrile butadiene styrene thermoplastic to unsaturated polyester thermoset are investigated for different processing conditions. The effect of processing temperature on the cure kinetics and interdiffusion kinetics are studied experimentally. The interphase thickness and microstructure are linked to the chemo-rheological properties of the materials. The interdiffusion mechanisms are explored and models are developed to predict the interphase thickness and microstructure for various process conditions. The temperature-dependent diffusivities were estimated by incorporating an inverse diffusion model. The mechanical response of interphases was analyzed by the Vickers microhardness test and was correlated to the processing condition and microstructure. It was observed that processing temperature has significant effect on the interdiffusion process and, consequently, on the interphase thickness, its microstructure and mechanical performance.

Wear Behavior of Rockforce Mineral Fiber and Mica Reinforced Polyamide-6 Composite against Thermoset Polyester Composite Disc

Elektrik sektöründe kullanma amaçlı gerçekleştirilen bu çalışmada ağırlık olarak % 20 oranında kaya yünü mineral elyaf (KYME) ve mika takviyeli poliamid-6 (PA-6) termoplastik esaslı polimer kompozitler, termoset esaslı kompozit disk yüzeyine karşı aşınma ve sürtünme davranışları incelenmiştir. Çalışmanın amacı elektrik sektörü için aşınma direnci daha iyi olan polimer kompozit malzeme ile termoset doymamış polyester kompozit çiftini belirlemektir. Tribolojik deneyler disk üzerinde pim düzeneği bulunan bir aşınma cihazında gerçekleştirilmiştir. Karşı disk malzeme olarak ağırlık olarak % 40 kalsiyum karbonat ve % 25 oranında uzun cam elyaf takviyeli doymamış polyester kompozit malzemesi kullanılmıştır. Tribolojik testler, 0,5 m/s kayma hızında 0,707, 1,415, 2,123 ve 3,538 MPa basınç altında gerçekleştirilmiştir. Yapılan tribolojik çalışmalar sonucunda en düşük aşınma oranı 1.98x10-14 m2/N değeri ile %20 oranında mika takviyeli PA-6 kompozitinde elde edilmiştir. Mika takviyeli PA-6 kompoziti kaya yünü mineral elyaf takviyeli kompozite göre yaklaşık olarak % 42 oranında daha az aşındığı belirlenmiştir. Yapılan çalışma sonucunda elektriksel uygulamalarda kullanım amaçlı üretilen kompozit malzemelerden % 20 mika takviyeli PA-6 kompoziti ile %40 kalsiyum karbonat ve % 25 oranında uzun cam elyaf takviyeli doymamış polyester kompozit malzeme çifti elektrik kontak kesicilerde kullanılabilecek en uygun malzeme olarak tespit edilmiştir.

Methacrylated lignosulfonate as compatibilizer for flax fiber reinforced biocomposites with soybean-derived polyester matrix

The poor adhesion between natural fibers and polymer matrix restricts the mechanical performance of natural fiber reinforced composites. Here, lignosulfonate was methacrylated and evaluated as a potential compatibilizer for flax fiber reinforced soybean-derived polyester thermosets. Significant improvement in both tensile and flexural properties of the fiber composites were achieved when the flax fiber mat was treated with methacrylated lignosulfonate solution. In particular, the flexural modulus and flexural strength more than doubled from 2.6 to 6.7 GPa and from 36 MPa to 76.8 MPa, respectively when the fibers were soaked in 5 wt % MLS solution. The SEM analysis revealed improved fiber-matrix interface and lower extent of fiber pull-out in the methacrylated lignosulfonate treated fiber composites, which correlates with the improved mechanical properties.