Polyols and polyurethanes prepared from epoxidized soybean oil ring‐opened by polyhydroxy fatty acids with varying OH numbers

Bio‐based polyols from epoxidized soybean oil and different fatty acids were successfully prepared using a solvent‐free method in order to investigate the effect of the polyols' OH numbers on the thermal and mechanical properties of the polyurethanes prepared using them. Epoxidized soybean oil/epoxidized linseed oil was ring‐opened by methanol/glycol followed by saponification to prepare polyhydroxy fatty acids. These fatty acids and epoxidized soybean oil were then used for further solvent‐free ring‐opening reactions with DBU as catalyst, which facilitated the carboxylic ring‐opening. Gel permeation chromatography revealed that a molar ratio of carboxylic acid from polyhydroxy fatty aicds and epoxy group of 0.5 : 1 resulted in optimized polyols containing the smallest amounts of residual starting materials. The obtained polyols had varying OH numbers and the acquired polyurethane films were comprehensively characterized. With increasing OH number of the polyols the PUs displayed an increase in crosslinking density, glass transition temperature (T_g), tensile strength and Young's modulus, and a decrease in elongation and toughness. This work provides Supporting Information on the effect of OH number of polyols obtained via a solvent‐free ring‐opening method on the mechanical and thermal properties of polyurethanes, of particular interest when designing PU products for specific purposes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41213.     

Synthesis of new polyester polyols from epoxidized vegetable oils and biobased acids

Biobased polyols were synthesized from reaction between epoxidized soybean oil and lactic, glycolic, or acetic acids. Polyols were characterized by NMR, alcohol and acid titration, and SEC. These analyses allowed to determine an average hydroxyl functionality between 4 and 5, with an oligomer content close to 50 wt%. Synthesized polyols were formulated with isocyanate to yield polyurethanes (PUs). Thermal and mechanical properties of obtained materials showed that synthesized polyols lead to rigid and brittle material with Young moduli higher than 900 N/mm² at RT and with T_g values around 50°C. Practical application: The products of the chemistry described in this contribution, i.e.: polyol from vegetable oils and lactic, glycolic, or acetic acids, provide biobased building blocks for further PUs syntheses by reaction with diisocyanates. The obtained PUs are partially biobased and may be applied as binders and coatings.     

Synthesis,characterization, and properties of polyols from hydrogenated terpinene–maleic ester type epoxy resin

Three kinds of polyfunctional polyols with hydroxyl values of 180–320 mg/g were prepared by the reaction of hydrogenated terpinene–maleic ester type epoxy resin with secondary amines (diethylamine, N‐methylethanolamine, and diethanolamine), and the chemical structures were characterized by Fourier transform infrared spectroscopy and NMR spectroscopy. These polyols were used in place of commonly used polyols to prepare two‐component polyurethanes when reacted with polyisocyanates. The crosslinking reactions of the polyols with polyisocyanate could be catalyzed by the tertiary amine groups included in the polyols, and the reaction rate was affected by hydrochloric acid and the polarity of the solvents. The mechanical, water‐resistance, and chemical‐resistance properties of the crosslinked products of the polyols were evaluated by standard tests, and the thermal properties were examined by differential scanning calorimetry and thermogravimetric analysis. The results show that these epoxy–urethane polymers, with glass‐transition temperatures (T_g's) in the range ?5 to 37°C, had good thermally resistant properties, and the temperatures at 5% weight loss were in the range 235–280°C. All of the polymers formed transparent, strong, flexible films, with good chemical‐resistance properties and excellent impact strengths of greater than 50 cm, a flexibility of 0.5 mm, adhesions of 1–2, and pencil hardnesses of HB–2H. The larger OH functionality and OH value of the polyol resulted in higher T_g and pencil hardness values and better alcohol resistance and thermal stability in the crosslinked product of the polyol. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and properties of polyurethane networks derived from new soybean oil‐based polyol and a bulky blocked polyisocyanate

BACKGROUND: Developing vegetable oil‐based polyols for polyurethane manufacturing is becoming highly desirable for both economic and environmental reasons. Most vegetable oils do not bear hydroxyls naturally. The objective of this work was to prepare a new soybean oil‐based polyol with high functionality of hydroxyl groups and built‐in (preformed) urethane bonds. RESULTS: A facile and improved method was developed for the transformation of epoxidized soybean oil into carbonated soybean oil under ambient pressure of CO₂ gas, with tetrabutylammonium bromide/calcium chloride as catalyst/co‐catalyst couple. Ring‐opening reaction of the carbonated oil with ethanolamine led to the desired polyol. A one‐pack polyurethane system was prepared via combination of the polyol and a blocked polyisocyanate. The polyol and final polyurethanes were fully characterized, and their physical, mechanical, viscoelastic and electrical insulating properties were studied. CONCLUSION: The application of this newly developed soybean oil‐based polyol for preparation of electroinsulating casting polyurethanes was examined. The prepared soy‐based polyurethanes offered excellent thermal and electrical insulating properties. Also, tunable physical and chemical properties for the final polyurethanes were achieved by replacing part of the soybean oil‐based polyol with poly(propylene glycol) (M_n = 1000 g mol^?1). Copyright © 2008 Society of Chemical Industry     

A simple one‐step synthesis and polymerization of plant oil triglyceride iodo isocyanates

In this study, a novel and simple route for the synthesis of the iodine isocyanate (INCO) adduct of soybean oil triglycerides is described. Soybean oil iodo isocyanate (ISONCO) was synthesized by the reaction of iodine isocyanate and soybean oil at room temperature. ISONCO was then polymerized with polyols, such as, castor oil, pentamethylene glycol, and glycerol to give the corresponding polyurethanes and with polyamines, such as, ethylene diamine, hexamethylene diamine, and triethylene tetramine to give corresponding polyureas. The structures of the monomer and the polymers were determined by FTIR and ¹H‐NMR analyses. Thermal properties of the polymers were determined by DSC and TGA. Thermal degradation of the polyurethanes started at 150°C. Stability of the polyureas was higher than polyurethanes. Almost all polymers showed a T_g around ?50°C. The mechanical properties of the polymers were determined by tensile tests. Among the polymers synthesized, castor oil polyurethane showed the highest elongation at break and the lowest tensile strength of 140 KPa. The highest tensile strength of 900 KPa was observed in the pentamethylene glycol polyurethanes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and Properties of Polyurethane Elastomers with Castor Oil as Crosslinker

Castor oil–polyurethane elastomers were prepared by reacting poly (1,4-butane diol) (Terathane 1400) with aliphatic 1,6-hexamethylene diisocyanate. The prepolymers were chain-extended with bifunctional precursor chains and/or with castor oil as a trifunctional crosslinker at stoichiometric ratios. These resulted in a series of crosslinked polyurethane elastomers with different structures of the hard segment. The properties of the material were measured by differential scanning calorimetry, thermogravimetric analysis, atomic force microscopy, as well as tensile properties measurements. The effect of stoichiometric balance (i.e., OH/NCO molar ratio) on the final properties was evaluated. The formation of hydrogen bonds was observed by Fourier transform infrared.spectroscopy The measured properties were found to be strongly influenced by the molar ratio of chain extenders to the diisocyanate component. The glass transition temperatures (T _g) for the polyurethanes with OH_polyol/NCO/OH_{chain extender} having molar ratios of 1:2:1 and 1:4:3 were found to be −70 and −57 °C, respectively. The polyurethanes networks with a OH/NCO molar ratio of 1:2:1 had excellent mechanical properties, indicating that this is the optimum ratio to be used in castor oil polyurethane elastomer formulations. The objective of this work was to study the effect of the castor oil crosslinker on the morphology of the resulting crosslinked polyurethanes and to correlate the morphology with the properties of these bio-based crosslinked polyurethanes.     

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     

Synthesis,physicochemical and thermal properties of urethane-modified polyesteramide films using mahua and castor oil as sustainable resources

In this work, a number of urethane-modified polyesteramide (UmPEA) films were developed from mahua and castor oils, which are renewable resources. Mahua oil and diethanolamine were reacted to form mahua fattyamide, which was then reacted with itaconic acid to prepare polyesteramide. In order to make the UmPEA films, different proportions of polyesteramide and castor oil as polyols were reacted with isophoronediisocyanate. The UmPEA films showed excellent chemical resistance against water, acid, alkali, salt, and organic solvents and were found insoluble in common organic solvents. The thermal stability of the UmPEA films was investigated through TGA and DSC analyses, and their T_g values are between 69.1°C and 56.1°C for UmPEA films, which indicated that a higher content of CO enhances the T_g, and it was also found that the films were highly stable up to 230°C. The E_a values [224 kJ mol⁻¹ (T_p1) and 226 kJ mol⁻¹ (T_p2)] indicate that the castor oil enhances the thermal stability of the films due to better cross-linking density occurring through the high hydroxyl groups of CO as the polyol which also showed better flame retardancy in the synthesized UmPEA films. Our findings demonstrate that the newly developed UmPEA films can be potent coating materials.     

Polyurethane foams from soyoil‐based polyols

The focus of this work was to synthesize bio‐based polyurethane (PU) foams from soybean oil (SO). Different polyols from SO were produced as follows: soybean oil monoglyceride (SOMG), hydroxylated soybean oil (HSO), and soybean oil methanol polyol (SOMP). The SOMG was a mixture of 90.1% of monoglyceride, 1.3% of diglyceride, and 8.6% of glycerol. The effect of various variables (polyol reactivity, water content curing temperature, type of catalyst, isocyanate, and surfactant) on the foam structure and properties were analyzed. SOMG had the highest reactivity because it was the only polyol‐containing primary hydroxyl (? OH) groups in addition to a secondary ? OH group. PU foams made with SOMG and synthetic polyol contained small uniform cells, whereas the other SO polyols produced foams with a mixture of larger and less uniform cells. The type of isocyanate also had an influence on the morphology, especially on the type of cells produced. The foam structure was found to be affected by the water and catalyst content, which controlled the foam density and the cure rate of the PU polymer. We observed that the glass transition (T_g) increased with the OH value and the type of diisocyanate. Also, we found that the degree of solvent swelling (DS) decreased as T_g increased with crosslink density. These results are consistent with the Twinkling Fractal Theory of T_g. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Properties of water‐blown rigid polyurethane foams with reactivity of raw materials

Rigid polyurethane foams (PUFs) were prepared from polymeric 4,4‐diphenylmethane diisocyanate (PMDI; having functionality of 2.9), polyether polyols, silicone surfactant, amine catalysts, and distilled water. The effects of reactivity on the properties such as density, compressive and flexural strength, and glass‐transition temperature (T_g) of the PUF samples were studied. The kinetic rate of forming the PUF samples was increased with the catalyst and water content. With increasing OH value and functionality of the polyols, the density and compressive strength of the PUF samples also increased. For the PUF samples synthesized with polyols having high functionality (>5), the flexural strength of the PUF samples decreased with the functionality of the polyols. With increasing OH value and functionality of the polyols, the T_g of the PUF increased because of an increase in the degree of crosslinking of the PUF samples. The T_g value and compressive strength of the PUF samples were observed to increase with the NCO index. From this result, it was suggested that the increase in the T_g value and compressive strength of the PUF samples may be attributable to the additional crosslinks that arose from allophonate and biuret formation by the supplementary reactions of excess PMDI. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2334–2342, 2004     

Effects of unsaturation and different ring-opening methods on the properties of vegetable oil-based polyurethane coatings

A variety of vegetable oil-based, waterborne polyurethane dispersions have been successfully synthesized from different vegetable oil polyols exhibiting almost constant hydroxyl functionalities of 2.7 OH groups per molecule. The vegetable oil polyols, which have been prepared from vegetable oils with different fatty acid compositions (peanut, corn, soybean, and linseed oil), range in residual degree of unsaturation from 0.4 to 3.5 carbon–carbon double bonds per triglyceride molecule. The effects of residual unsaturation on the thermal and mechanical properties of the resulting polyurethane films have been investigated by dynamic mechanical analysis, differential scanning calorimetry, and thermal gravimetric analysis. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) has been used to accurately determine the molecular weight and mass distribution of the vegetable oil polyols. Higher residual unsaturation results in polyurethane films with increased break strength, Young's modulus, and toughness. This work has isolated the effect of unsaturation on vegetable oil-based polyurethane films, which has been neglected in previous studies. The effect of different oxirane ring opening methods (methanol, butanol, acetic acid, and hydrochloric acid) on the properties of the coatings has also been examined.     

Thermal transition behavior of polybutadiene containing polyurethanes

The thermal transition behavior of a series of hydroxy terminated polybutadiene (HTPBD) containing segmented polyurethanes has been studied by differential scanning calorimetry (DSC) and thermal mechanical analysis (TMA). Four transition regions are observed; the soft segment T_g, at ?74°C, two hard segment transitions T₁, at 40°C and T₂ at 103°C and a softening region by TMA at 180°C, presumed to arise from the dissociation of allophonate bonding, The low T_g, only 7°C higher than the T_g of free HTPBD, indicates nearly complete phase segregation despite the amorphous nature of the hard segment structure. The dependence of T₁, on hard segment length and thermal cycling suggests that it represents domains consisting primarily of shorter hard segments units. Factors contributing to the rather low mechanical properties of HTPBD polyurethanes are also discussed.     

Physical Properties of Polyurethanes Produced from Polyols from Seed Oils: I. Elastomers

Polyols synthesized by ozonolysis and hydrogenation from canola oil were reacted with aliphatic 1,6-hexamethylene diisocyanates (HDI) to produce polyurethane (PU) elastomers. The properties of the materials were examined by dynamic mechanical analysis (DMA), thermomechanical analysis (TMA), modulated differential scanning calorimetry (MDSC), and thermogravimetric analysis (TGA), and measurements were taken of tensile properties. The effect of dangling chains on network properties was assessed. The formation of hydrogen bonds was observed by FTIR. The measured properties were found to be strongly dependent on processing-dependent factors such as the crosslinking density and the molar ratio of polyols to HDI component. The glass transition temperatures (T _g) of the elastomers were found to increase as the OH/NCO molar ratio decreased. With the same OH/NCO molar ratio, T _g of canola-oil-based PU was higher than that of soybean-oil-based PU. The TGA thermographs showed two well-defined steps of degradation for all the elastomers. In the first step, up to 30% weight loss, the fastest rate of loss was found at 345 °C for canola-oil-based PU while soybean-oil-based PU lost most of the weight in the second step. With the same OH/NCO molar ratio, the elastomers made from canola-oil-based polyol showed slightly higher Young’s modulus and tensile strength.     

Polyurethane networks from polyols obtained by hydroformylation of soybean oil

BACKGROUND: Vegetable oil‐based polyols are a new class of renewable materials. The structure of oil‐based polyols is very different from that of petrochemical polyols, and it is closely related to the structure of oils. The objective of this work was to analyze the structural heterogeneity of soy‐based polyols and its effect on the properties of polyols and polyurethanes. RESULTS: A series of polyols with a range of hydroxyl numbers were prepared by hydroformylation and partial esterification of hydroxyls with formic acid. Polyols were reacted with diphenylmethane diisocyanate to obtain polyurethanes of different crosslinking density. Gelation was simulated using the Monte Carlo method with a calculated distribution of functionalities for each polyol. CONCLUSIONS: Most polyols are powerful crosslinkers since weight average functionality varied from 5 to 2.5 resulting in gel points from 53 to 83% conversion. Heterogeneity of polyols had a negative effect on mechanical properties of rubbery polyurethanes and this should be taken in account when designing polyols for flexible applications. This effect was not pronounced in glassy polyurethanes. Copyright © 2007 Society of Chemical Industry     

Thermomechanical behavior of epoxy resins modified with epoxidized vegetable oils

Biobased epoxy materials were prepared from diglycidyl ether of bisphenol A (DGEBA) and epoxidized vegetable oils (EVOs) (epoxidized soybean oil and epoxidized castor oil) with a thermally latent initiator. The effects of EVO content on the thermomechanical properties of the EVO‐modified DGEBA epoxy resins were investigated using several techniques. Differential scanning calorimetry indicated that the cure reaction of the DGEBA/EVO systems proceeded via two different reaction mechanisms. Single and composition‐dependent glass transition temperature (T_g) mechanisms were observed for the systems after curing. The experimental values of T_g could be explained by the Gordon–Taylor equation [Gordon M and Taylor JS, J Appl Chem 2 :493 (1952)]. The thermal stability of the systems decreased as the EVO content increased, due to the lower crosslinking density of the DGEBA/EVO systems. The coefficient of thermal expansion of the systems was found to increase linearly with increasing EVO content. This could be attributed to the fact that the degrees of freedom available for motions of the segments of the macromolecules in the network structure were enhanced by the addition of EVO. Copyright © 2008 Society of Chemical Industry     

Bio‐Based,Self‐Condensed Polyols

A new method for the synthesis of high‐molar‐mass (MM), bio‐based polyols for elastic polyurethanes is developed. This process is based on the self‐condensation of low MM polyols (M_n ≈ 1000) and vacuum removal of the resulting glycerol. Self‐condensation products are hyperbranched estolide polyols with average MMs close to 3000 and hydroxyl numbers in the range of 40–95 mg KOH g^?1. Three polyols, one with primary and two with secondary hydroxyls and different functionalities, are studied. The transesterification proceeded much faster with primary hydroxyls, leading to high‐viscosity products. The effect of functionality and reactivity of starting polyols on properties is discussed. Practical applications: The process is useful for upgrading the existing natural oil‐based polyols to higher MM, lower OH number and variable‐functionality polyols, for expanding application in the urethane field. The process is simple, involving just an oil‐based polyol, a catalyst, and heating under vacuum.     

Synthesis and properties of polyurethane elastomers based on renewable castor oil polyols

In this contribution, castor oil polyols with functionality of f = 2.7 and f = 2 are used as soft segments (SS) for synthesizing polyurethane elastomers (PUEs) without addition of petroleum-based polyol. The effect of molar ratio of castor oil polyols on structure and properties of PUEs has been investigated by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, X-ray diffraction, tensile, swelling, and water absorption tests. The results reveal that hydrogen bonding mainly exists in hard segments (HSs) and weakens with decreasing the molar percentage of castor oil polyol (f = 2.7) in SS. T _g of SS decreases while T _g of HS remains constant as molar percentage of castor oil polyol (f = 2.7) decreased. The initial degradation temperatures (T_5%) are above 300 °C and independent of the molar ratio of castor oil polyols. However, the temperature at 50% weight loss (T_50%) decreases significantly as molar percentage of castor oil polyol (f = 2.7) decreased. Moreover, PUEs exhibit very low water absorption rate, <1%, after immersing in water for 140 h at room temperature. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47309.     

Vinyl ether‐based polyacetal polyols with various main‐chain structures and polyurethane elastomers prepared therefrom: Synthesis,structure, and functional properties

Novel acid degradable polyacetal polyols and polyacetal polyurethanes able to controlled acid degradation were developed. Polyacetal polyols with various main‐chain structures were synthesized by polyaddition of various vinyl ethers with a hydroxyl group [4‐hydroxy butyl vinyl ether (CH₂?CH? O? CH₂CH₂CH₂CH₂? OH), 2‐hydroxy ethyl vinyl ether (CH₂?CH? O? CH₂CH₂? OH), diethylene glycol monovinyl ether (CH₂?CH? O? CH₂CH₂OCH₂CH₂? OH), and cyclohexanedimethanol monovinyl ether (CH₂?CH? O? CH₂? C₆H₁₀? CH₂? OH)] with p‐toluenesulfonic acid monohydrate (TSAM) as a catalyst in the presence of the corresponding diols [1,4‐butandiol (HO? CH₂CH₂CH₂CH₂? OH), ethylene glycol (HO? CH₂CH₂? OH), diethylene glycol (HO? CH₂CH₂OCH₂CH₂? OH), and 1,4‐cyclohexanedimethanol (HO? CH₂? C₆H₁₀? CH₂? OH)], respectively. Polyacetal polyurethanes were prepared by a two‐step polymerization, using the synthesized polyacetal polyols, 4,4′‐diphenylmethane diisocyanate (MDI), and 1,4‐butandiol (BD) as a chain extender. Depending on the main‐chain structures, these polyurethanes had different glass transition temperature (from ?44 to 19 °C) and properties such as hydrophobic or hydrophilic. Polyurethanes containing the hydrophilic main‐chain exhibited the thermoresponsiveness and had the certain volume phase transition temperature (VPTT). The polyacetal polyurethanes were flexible elastomers around room temperature (～25 °C) and thermally stable (T_d ≥ 310 °C) and additionally exhibited smooth degradation with a treatment of aqueous acid in THF at room temperature to give the corresponding raw material diols. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44088.     

Synthesis and properties of cross‐linked polymers from epoxidized rubber seed oil and triethylenetetramine

A series of epoxidized oils were prepared from rubber seed, soybean, jatropha, palm, and coconut oils. The epoxy content varied from 0.03 to 7.4 wt %, in accordance with the degree of unsaturation of the oils (lowest for coconut, highest for rubber seed oil). Bulk polymerization/curing of the epoxidized oils with triethylenetetramine (in the absence of a catalyst) was carried out in a batch setup (1 : 1 molar ratio of epoxide to primary amine groups, 100°C, 100 rpm, 30 min) followed by casting of the mixture in a steel mold (180°C, 200 bar, 21 h) and this resulted in cross‐linked resins. The effect of relevant pressing conditions such as time, temperature, pressure, and molar ratio of the epoxide and primary amine groups was investigated and modeled using multivariable nonlinear regression. Good agreement between experimental data and model were obtained. The rubber seed oil‐derived polymer has a T_g of 11.1°C, a tensile strength of 1.72 MPa, and strain at break of 182%. These values are slightly higher than for commercial epoxidized soybean oil (T_g of 6.9°C, tensile strength of 1.11 MPa, and strain at break of 145.7%). However, the comparison highlights the potential for these novel resins to be used at industrial/commercial level. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42591.     

Recent studies on interpenetrating polymer networks

Recent investigations on interpenetrating polymer networks (IPNs) have included two component IPNs from polyurethanes and poly(methacrylates) and two component IPNs from polyurethanes and epoxies. All the IPNs were prepared by the simultaneous polymerization technique (SIN-IPNs). Two types of IPNs, polyurethane-poly(methyl methacrylate) (PU/PMMA) and polyurethane-poly(methyl methacrylate-methacrylic acid) (PU/PMMA-MAA) were prepared. Improved phase miscibility and decreasing extent of phase separation was observed in both types of IPNs with increasing the NCO/OH ratio, decreasing molecular weight of the polyol in the PU and introduction of charge groups. A comparison was made between full-IPNs, pseudo-IPNs, graft copolymers and related homopolymers from polyurethanes and epoxies. Increased compatibility in full-IPNs and graft copolymers was observed by means of DSC, SEM and was also further substantiated by a shift toward single T_gs as determined by dynamic mechanical spectroscopy. The introduction of opposite charge groups in two-component IPNs from polyurethanes and epoxies led to improved compatibility (no phase separation) and enhanced mechanical properties.