New sheet molding compound resins from soybean oil. I. Synthesis and characterization

Thermosetting resins were synthesized from soybean oil, which are suited to sheet molding compound (SMC) applications. It was achieved by introducing acid functionality and CC groups onto triglyceride molecules. The acid groups can react with divalent metallic oxides and/or hydroxides to form the sheet, while CC groups undergo free radical polymerization. An acrylated epoxidized soybean oil (AESO), which has an average of 3.4 acrylates per triglyceride, was used as starting material. The hydroxyl groups on AESO reacted with maleic anhydride (MA) to render acid groups on the molecule. The resulting monomer was then copolymerized with 33 wt% styrene to form rigid polymers. Dynamic mechanical analysis showed storage moduli (E′) for these polymers ranging from 1.9 to 2.2 GPa at room temperature, and the glass transition temperatures (T_g) in the range of 100-115 °C. Both the E′ and T_g were increased by increasing the molar ratio of MA to AESO, and the transition from the glassy to the rubbery state was broadened by increasing the amount of MA. The effect of styrene as a comonomer was also examined, and a final formulation for SMC was optimized. The resulting resins exhibited appropriate viscosity during the SMC thickening process.     

Soybean‐ and castor‐oil‐based thermosetting polymers: Mechanical properties

Maleic anhydride modified soybean‐ and castor‐oil‐based monomers, prepared via the malination of the alcoholysis products of the oils with various polyols, such as pentaerythritol, glycerol, and bisphenol A propoxylate, were copolymerized with styrene to give hard rigid plastics. These triglyceride‐based polymers exhibited a wide range of properties depending on their chemical structure. They exhibited flexural moduli in the 0.8–2.5 GPa range, flexural strength in the 32–112 MPa range, glass transition temperatures (T_g) ranging from 72 to 152°C, and surface hardness values in the 77–90 D range. The polymers prepared from castor oil exhibited significantly improved modulus, strength, and T_g values when compared with soybean‐oil‐based polymers. These novel castor and soybean‐oil‐based polymers show comparable properties to those of the high‐performance unsaturated polyester (UP) resins and show promise as an alternative to replace these petroleum‐based materials. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1497–1504, 2006     

Thermosetting allyl resins derived from soybean fatty acids

A novel class of thermosetting resins based on allylated and transesterified epoxidized soybean oil (AE‐ESBO) curable by radical mechanism was developed. The AE‐ESBO was prepared from ESBO by oxirane ring‐opening and then transesterification with allyl alcohol. A family of rubbery to glassy resins was prepared by radical copolymerization of AE‐ESBO with different concentrations of maleic anhydride (MA). Glass transition temperatures (T_g) of these resins ranged from below room temperature to about 130°C based on the amount of MA. In spite of the presence of anhydride groups, water absorption was low <2% even when maleic anhydride was 30% of total weight. Low sol content after extraction and low swelling in toluene indicated high crosslinking density. Tensile moduli of these resins were up to 1.4 GPa and tensile strengths up to 37 MPa. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Biobased composites prepared by compression molding with a novel thermoset resin from soybean oil and a natural‐fiber reinforcement

Biobased composites were manufactured with a compression‐molding technique. Novel thermoset resins from soybean oil were used as a matrix, and flax fibers were used as reinforcements. The air‐laid fibers were stacked randomly, the woven fabrics were stacked crosswise (0/90°), and impregnation was performed manually. The fiber/resin ratio was 60 : 40. The prepared biobased composites were characterized by impact and flexural testing. Scanning electron microscopy of knife‐cut cross sections of the specimens was also done to investigate the fiber–matrix interface. Thermogravimetric analysis of the composites was carried out to provide indications of thermal stability. Three resins from soybean oil [methacrylated soybean oil, methacrylic anhydride modified soybean oil (MMSO), and acetic anhydride modified soybean oil] were used as matrices. The impact strength of the composites with MMSO resin reinforced with air‐laid flax fibers was 24 kJ/m², whereas that of the MMSO resin reinforced with woven flax fabric was between 24 and 29 kJ/m². The flexural strength of the MMSO resin reinforced with air‐laid flax fibers was between 83 and 118 MPa, and the flexural modulus was between 4 and 6 GPa, whereas the flexural strength of the MMSO resin reinforced with woven fabric was between 90 and 110 MPa, and the flexural modulus was between 4.87 and 6.1 GPa. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Novel thermosetting resins for SMC applications from linseed oil: Synthesis,characterization, and properties

New thermosetting resins for applications of sheet‐molding compounds (SMCs) were successfully synthesized from linseed oil, which is the most molecularly unsaturated of all plant oils. The carbon–carbon double bonds were opened by epoxidation, followed by acrylation, and then maleinization, which provided more crosslink sites and added acid functionality on the triglyceride molecules to develop thickening. Dynamic mechanical analysis showed that the storage modulus of these new polymers was approximately 2.5 GPa at 30°C, and the glass‐transition temperature was above 100°C. During maturation the resins reached a molding viscosity quickly and stayed stable. Mechanical tests showed a flexural strength of 100 MPa and a flexural modulus of 2.8 GPa. Thermogravimetric analysis showed a single degradation ranging from 300°C–480°C, which was a result of the carbonization of the crosslinked network. These bio‐based resins are promising as replacements of some petroleum‐based resins in the SMC industry. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Catalyzed crosslinking of highly functional biobased epoxy resins

Crosslinking reactions involving epoxy homopolymerization of 100% biobased epoxidized sucrose esters (ESEs) were studied and the resulting coatings properties were compared against epoxidized soybean oil (ESO) and petrochemical-based soybean fatty acid ester resins. The low viscosity of ESE resins allowed for formulations to be developed with minimal volatile organic content. ESEs were found to have superior coatings properties, compared to ESO and the petrochemical-based soybean esters, attributable to a higher glass transition temperature (T _g) and a higher modulus. The rigid sucrose core on ESEs provided an increase in coating performance when compared to coatings from epoxidized resins synthesized with tripentaeryithritol as a core. The degree of conversion and optimization of the curing conditions were studied using differential scanning calorimetry (DSC). Thermal analysis of cured coatings was performed using DSC, dynamic mechanical analysis, and thermogravimetric analysis. In order to further enhance the coatings properties, small amounts of bisphenol A epoxy resin were added which resulted in higher moduli and T _gs.     

Application of factorial design to SMC viscosity build-up

Summary The thickening behavior of SMC varies with formulation and operating conditions. During the SMC compounding process, alkaline oxides such as MgO, Mg(OH)₂, CaO, Ca(OH)₂ are added to the formulation to yield the viscosity build-up from a flowable paste to a semi-solid sheet. The thickening curve of SMC can be divided into three stages: 1. The initial thickening period for the wetting process, 2. The middle thickening rate period for viscosity increasing, 3. The final viscosity period for the molding process. By means of factorial design with an appropriate objective set-up, one is able to define the influence of each factor on thickening curves. Combined with the experimental work on some individual factors, the maturation control system can be further understood and the proper thickening rates can be obtained.     

Effect of maleated polypropylene as coupling agent for polypropylene composites reinforced with hemp strands

New composites based on poly(propylene) as polymer matrix and hemp strands as natural reinforcement have been developed by injection‐molding. The materials were previously mixed in a two roll mill to induce the dispersion of the fiber inside the polymer. To improve the adhesion between both components, maleated poly(propylene) was added as coupling agent, at 4% wt/wt with respect to hemp strands. The addition of this amount of this coupling agent to the formulation modified with 40 wt % of hemp strands increases the ultimate tensile strength (σ_t) and flexural strength (σ_f) up to 49 and 38%, respectively, compared with the composite without coupling agent. The interaction between the surface of hemp strands and the coupling agent was determined by FT‐IR spectroscopy assuming that a covalent bond was established, avoiding the adverse effect of the poor compatibility at the interface for this kind of composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 833–840, 2006     

Highly functional lactic acid ring-opened soybean polyols applied to rigid polyurethane foams

We synthesized polyols with high hydroxyl functionalities (F_OHs), between 9.0 and 12.6, and characterized them with differential scanning calorimetry, thermogravimetric analysis, and size exclusion chromatography after we parametrically studied the ring-opening reaction of epoxidized soybean oil with lactic acid (LA) as a function of the reaction temperature and lactic acid equivalent fraction (f_LA). An increase of only 20°C in the reaction temperature (from 80 to 100°C) caused changes in the hydroxyl number (+17.8%), F_OH (–25%), viscosity (–14.0%), and oligomeric content (–24.1%). f_LA mostly affected the ring-opening yield, and only for f_LA values above 0.4 was possible to achieve values higher than 80%. Rigid polyurethane foams (rPUFs) were synthesized and characterized with scanning electron microscopy, dynamic mechanical analysis (DMA), and compressive mechanical tests. rPUFs with a very high specific compressive strength (7.8 kPa kg^–1 m³) were synthesized solely with biobased soybean oil. DMA revealed a compromised relationship between the specific compressive strength and its temperature dependence. To increase the first one, the most relevant method was to increase F_OH. Instead, to increase the latter one, the OH number had to be maximized. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47959.     

Fatty acid‐based comonomers as styrene replacements in soybean and castor oil‐based thermosetting polymers

In this study, a fatty acid‐based comonomer is employed as a styrene replacement for the production of triglyceride‐based thermosetting resins. Styrene is a hazardous pollutant and a volatile organic compound. Given their low volatility, fatty acid monomers, such as methacrylated lauric acid (MLA), are attractive alternatives in reducing or eliminating styrene usage. Different triglyceride‐derived cross‐linkers resins were produced for this purpose: acrylated epoxidized soybean oil (AESO), maleinated AESO (MAESO), maleinated soybean oil monoglyceride (SOMG/MA) and maleinated castor oil monoglyceride (COMG/MA). The mechanical properties of the bio‐based polymers and the viscosities of bio‐based resins were analyzed. The viscosities of the resins using MLA were higher than that of resins with styrene. Decreasing the content of MLA increased the glass transition temperature (T_g). In fact, the T_g of bio‐based resin/MLA polymers were on the order of 60°C, which was significantly lower than the bio‐based resin/styrene polymers. Ternary blends of SOMG/MA and COMG/MA with MLA and styrene improved the mechanical properties and reduced the resin viscosity to acceptable values. Lastly, butyrated kraft lignin was incorporated into the bio‐based resins, ultimately leading to improved mechanical properties of this thermoset but with unacceptable increases in viscosity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The rheology and mold flow of polyester sheet molding compound

Flow properties of sheet molding compounds (SMC) were measured by several rhemeters. Shear viscosities of SMC paste can be fitted by the Carreau viscosity equation and reduced to a single master curve by plotting the reduced shear viscosity (η/η₀) against reduced shear rate (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} η₀/T). The deformation fo glass filled compounds under extensional forces. When the shear forced was applied, the compound defomed like a deck of cards being slid. It behaved essentially like a laminate of many layers. On the other hand, SMC compounds elongated much less before sample failure occurred under the extensional flow. The extensional viscosity was much higher than the shear viscosity. This phenomenon was explained by a solid composite theory and theories developed from local shear flows between adjacent fibers. The flow of SMC compounds during molding showed that the surface layers flowed further than the inner layers when the mold surfaces were hot. This casued inner plies to show through at the surface and resulting in some wavy glass orientation. This phenomenon was explained equalitatively by a heat penetration model.     

Synthesis of reactive soybean oils for use as a biobased thermoset resins in structural natural fiber composites

Biobased thermosets resins were synthesized by functionalizing the triglycerides of epoxidized soybean oil with methacrylic acid, acetyl anhydride, and methacrylic anhydride. The obtained resins were characterized with FTIR, ¹H‐NMR, and ¹³C‐NMR spectroscopy to confirm the functionalization reactions and the extent of epoxy conversion. The viscosities of the methacrylated soybean oil resins were also measured for the purpose of being used as a matrix in composite applications. The cross‐linking capability was estimated by UV and thermally initiated curing experiments, and by DSC analysis regarding the degree of crosslinking. The modifications were successful because up to 97% conversion of epoxy group were achieved leaving only 2.2% of unreacted epoxy groups, which was confirmed by ¹H‐NMR. The ¹³C‐NMR confirms the ratio of acetate to methacrylate methyl group to be 1 : 1. The viscosities of the methacrylated soybean oil (MSO) and methacrylic anhydride modified soybean oil (MMSO) were 0.2 and 0.48 Pas, respectively, which indicates that they can be used in resin transfer molding process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

First principles calculation of single‐crystal elastic constants of titanium tetraboride (Ti3B4) and experimental validation

The nine independent single‐crystal elastic constants of a new ceramic, titanium tetraboride (Ti₃B₄), have been determined by first principles calculations, and the data were validated experimentally through nanoindentation testing. The independent elastic constants, which are specific to the crystal structure, are important for the fundamental characterization of mechanical and physical properties of the group of hard compounds such as the transition metal borides. The elastic constants of Ti₃B₄ were determined from crystal strain energies that were calculated by applying specific deformations within WIEN2k platform utilizing full‐potential linear augmented plane wave (FLAPW) and generalized gradient approximation (GGA). The WIEN2K package is based on all‐electron calculations, and hence is considered as the most accurate for first principles calculations. It has been found that the polycrystalline elastic moduli, determined as the Voigt‐Reuss‐Hill averages of the independent elastic constants, are quite impressive (E = 492 GPa, G = 217 GPa, B = 224 GPa, ν = 0.13) placing the tetraboride very close to the well‐known titanium diboride (E = 570 GPa, G = 254 GPa, B = 249 GPa, ν = 0.12). The strong B‐B chains were found to be largely responsible for the high values of elastic stiffness constants, in particular the c₃₃ describing stiffness in the [001] direction. The electron charge densities were found to be accumulated to a higher degree along the B‐B bonds, resulting in strengthening of the B‐B chains in the lattice. The promising data motivated the first experimental synthesis of Ti₃B₄ in a bulk form, which is also described in this work. To validate the elastic constants determined from first principles, elastic moduli were determined by nanoindentations in multiple grains of a polycrystalline Ti₃B₄, synthesized by electric field‐activated reaction sintering. The range of elastic moduli determined from nanoindentation was found to agree well with the range determined by computation. The calculations and experiments demonstrate that Ti₃B₄ has the potential to be one of the leading structural ceramics.     

Tensile and Impact Properties of Hollow Glass Bead‐Filled PVC Composites

The tensile and notched Izod impact properties of poly(vinyl chloride) (PVC) composites filled with hollow glass beads (HGB) were measured at room temperature by means of an Instron materials testing machine to investigate the effects of the filler content and size on these mechanical properties. The results showed that the tensile yield strength (σ_yc) decreased gently with increasing HGB volume fraction (ϕ _f), while the tensile break strength (σ_bc) of the composites was somewhat greater than that of the unfilled PVC within ϕ _f = 0–20%. In addition, the dependence of σ_bc on ϕ _f was not obvious. The effect of HGB size on both σ_yc and σ_bc was insignificant. When ϕ _f < 5%, the notched impact strength (σ_IC) of the composites decreased quickly with increasing ϕ _f, and then it decreased slightly with the increase of ϕ _f. Similarly, the influence of the filler size on the impact properties was insignificant. Furthermore, the σ_yc of the samples was estimated using a tensile equation proposed in a previous paper. A good agreement was shown between the calculations and the measured data.     

Development and application of triglyceride-based polymers and composites

Triglyceride oils derived from plants have been used to synthesize several different monomers for use in structural applications. These monomers have been found to form polymers with a wide range of physical properties. They exhibit tensile moduli in the 1–2 GPa range and glass transition temperatures in the range 70–120 °C, depending on the particular monomer and the resin composition. Composite materials were manufactured utilizing these resins and produced a variety of durable and strong materials. At low glass fiber content (35 wt %), composites produced from acrylated epoxidized soybean oil by resin transfer molding displayed a tensile modulus of 5.2 GPa, a flexural modulus of 9 GPa, a tensile strength of 129 MPa, and flexural strength of 206 MPa. At higher fiber contents (50 wt %) composites produced from acrylated epoxidized soybean oil displayed tensile and compression moduli of 24.8 GPa each, and tensile and compressive strengths of 463.2 and 302.6 MPa, respectively. In addition to glass fibers, natural fibers such as flax and hemp were used. Hemp composites of 20% fiber content displayed a tensile strength of 35 MPa and a tensile modulus of 4.4 GPa. The flexural modulus was ∼2.6 GPa and the flexural strength was in the range 35.7–51.3 MPa, depending on the test conditions. The flax composite materials had tensile and flexural strengths in the ranges 20–30 and 45–65 MPa, respectively. The properties exhibited by both the natural- and synthetic fiber-reinforced composites can be combined through the production of “hybrid” composites. These materials combine the low cost of natural fibers with the high performance of synthetic fibers. Their properties lie between those displayed by the all-glass and all-natural composites. Characterization of the polymer properties also presents opportunities for improvement through genetic engineering technology. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 703–723, 2001     

Fabrication of TiC coated short carbon fiber reinforced Ti3SiC2 composites: Process,microstructure and mechanical properties

The C_f/Ti₃SiC₂ composites were fabricated through spark plasma sintering (SPS) and hot isostatic pressing (HIP), TiC coated C_f and Ti₃SiC₂ powder were used as starting materials. The improved fracture toughness (K_IC) and Vickers hardness (HV₁) of the TiC coated C_f/Ti₃SiC₂ composite fabricated by SPS were 7.59 MPa·m^1/2 and 7.28 GPa. On this foundation, taking the advantage of better sintering process of HIP, the highest K_IC and HV₁ achieved 8.32 MPa·m^1/2 and 9.24 GPa with fiber content of 10 vol%, which increased by 40% and 65% compared with that of monolithic Ti₃SiC₂. The reasonable control of reactive interface is the main factor for the improved mechanical properties of the composites, the TiC coating effectively protected the fiber structure from interfacial reaction compared with that of the non-coated C_f/Ti₃SiC₂. Meanwhile, the artificially designed and weakly bonded TiC coated C_f can fully exert the toughening mechanisms like fiber pull-out and debonding.     

Auxetic polypropylene films

Auxetic materials are those exhibiting negative Poisson's ratio (ν) behavior. Polymeric auxetic extruded products in the form of cylinders and fibers have previously been reported. This article reports the successful production of auxetic polypropylene films (～0.15‐mm thick) using a melt extrusion process. Video extensometry and tensile testing techniques have been used to measure the in‐plane Poisson's ratios and Young's moduli of the auxetic film, both on an Instron tensile testing machine and a Deben microtensile testing machine. The film is elastically anisotropic with the Poisson's ratio and Young's modulus along the extrusion (x) direction being ν_xy = ?1.12 ± 0.06 and E_x = 0.34 ± 0.01GPa, respectively, while the Poisson's ratio and Young's modulus in the transverse (y) direction to the extrusion direction are ν_yx = ?0.77 ± 0.01 and E_y = 0.20 ± 0.01GPa, respectively. POLYM. ENG. SCI., 45:517–528, 2005. © 2005 Society of Plastics Engineers     

Tension–compression anisotropy of in-plane elastic modulus for pyrolytic carbon

We used standard strain gage methods to measure the anisotropic elastic constants for a sample of pyrolytic carbon. The in-plane elastic modulus exhibits significant tension–compression anisotropy −30.2 GPa in tension and 18.8 GPa in compression. The out-of-plane compressive modulus is 5.2 GPa and the Poisson’s ratios are ν₁₂ = 0.35 (compression), ν₂₃ = 0.16 (tension), 0.22 (compression), and ν₂₁ = 0.97 (tension). The tension–compression anisotropy is attributed to buckling, puckering, or bending of the graphene sheets in compression versus simple stretching in tension. The in-plane to out-of-plane anisotropy is expected from the microstructural anisotropy.     

Unsaturated polyester resins for thermoset applications using renewable isosorbide as a component for property improvement

Unsaturated polyester (UPE) resins are used in a variety of thermosetting applications due to the reduced cost when compared to epoxy resins; however, UPE resins also have reduced thermomechanical performance. Investigating avenues to improve the performance of UPEs has led to the use of bio‐based starting materials as structural components of the synthesized prepolymers as a result of their advantageous structural features. Isosorbide, a compound derived from renewable feedstocks, has been utilized to provide additional stiffness from the diol component for novel unsaturated polyesters resins. These resins have been shown to possess T_g's (32?72°C) and storage moduli (540?2200 MPa) that are in the desired range for composite materials with viscosities (1.2?25 Pa s) amenable to a variety of liquid molding techniques. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42315.     

Effects of Monoacylglycerols on Kinematic Viscosity and Cold Filter Plugging Point of Biodiesel

Biodiesel is an alternative fuel composed of mono‐alkyl fatty acid esters made from the transesterification of plant oils or animal fats with methanol or ethanol. After conversion, biodiesel may contain trace concentrations of unconverted monoacylglycerols (MAG). These MAG have low solubility in biodiesel and may form solid residues when stored at cold temperatures. The present study evaluates the measurement of kinematic viscosity (ν) and cold filter plugging point (CFPP)‐time to filter (Δt) as parameters that predict the temperature where small concentrations of MAG may lead to formation of solids or other phase transitions that restrict the flow of soybean oil fatty acid methyl esters (SME) through filters and fuel lines. Mixtures of SME doped with MAG were prepared and ν and Δt were measured as the temperature decreased from 20 to below 0 °C. Results showed a correlation between ν and Δt that held for neat SME (SME without added MAG) and SME‐MAG mixtures as the temperature decreased to the threshold temperature (T_th). Sharp increases in Δt disrupted the correlation as temperature decreased below T_th. Furthermore, T_th generally increased as added MAG concentration increased in the mixtures.