Some Effects of Structure,Composition and Cure on the Water Absorption and Glass Transition Temperature of Amine-cured Epoxies

The effect of structure, composition, and cure on the water absorption and T_g of amine-cured epoxies was investigated. Water absorption is considered to depend on the polar group concentration and type, and on the amount of free volume in the polymer network. The contribution of polar groups in terms of their hydrogen bonding capabilities is reflected by the effect of meta (with respect to the diglycidylamino group) chloro, bromo, and methyl substituents on the water absorption of bis[N,N-bis(2,3-epoxypropyl)-4-aminophenyl]methane cured with 4,4′-diaminodiphenylsulphone. The observed water absorptions are in line with the expected electronic effects of the substituents on the basicity of the amine group. Substituents in the ortho position adversely affect the hydrogen bonding capability of the amine group and limit the extent of reaction by steric interference. Examination of four O-glycidyl systems (Epon 825, Epon 1153/114, Epon 1031, and Dow XD-7342) cured with 4,4′-diaminodiphenylsulphone has revealed quite a good linear relationship between the equilibrium water absorption and T_g for a particular hardener concentration irrespective of the epoxy compound employed. Networks ranged from those of low T_g (110°C) and water absorption (1.3%) to those of high values (300°C and 6.1%) for these parameters. Differences in slope for low (50-65%) and high (100%) stoichiometric amounts of hardener are attributed to differences in the relative importance of OH/epoxy and NH₂ or NH/epoxy reactions. The theoretical polar group concentrations and polar group type are much the same for these different systems and thus, free volume is considered to be a function of T_g and to play an important part in determining the level of water absorption.     

Polar and nonpolar parameters for polymeric reverse osmosis membrane materials from liquid chromatographic data

Polar (α_p) and nonpolar (α_n) parameters to characterize a variety of cellulosic and noncellulosic polymers have been developed from liquid chromatographic data on retention times for selected reference solutes in aqueous solutions. The above parameters give relative quantitative measures for the hydrogen bonding and nonpolar (hydrophobic) forces inherent in the chemical structure of the polymer molecule. Unique correlations are also shown to exist between the above parameters and Hansen's solubility parameters δ_h and δ_d for the polymers. These parameters and correlations offer significant guidelines for the choice of membrane material for reverse osmosis.     

Enskog modulus,bρχ, for the gaseous and liquid states of carbon dioxide

The PVT behavior of carbon dioxide was used to establish a correlation for the Enskog modulus, bρχ in the dense gaseous and liquid regions. This modulus is presented for reduced temperatures ranging from T_R = 0.90 up to T_R = 3.5 and reduced pressures up to P_R = 40. The Enskog modulus finds use in the calculation of the effect of pressure on viscosity, thermal conductivity, and self-diffusivity. The value of the Enskog modulus for carbon dioxide at the critical point has been calculated to be (bρχ)_c = 0.885.     

Structure evolution and electric-field-induced reversible transition in perovskite Na(Nb1−xTax)O3 ceramics

Na(Nb_1−xTa_x)O₃ binary solid-solution ceramics with high quality were fabricated by conventional solid-state sintering routes for improving the electric(E)-field-induced irreversible polarization and transition behaviors of NaNbO₃. The studied results confirm that this binary solid-solution ceramics exhibit orthorhombic Pbcm space group companying with reduced unit-cell volume at x ≤ 0.4, and orthorhombic Pbnm space group at x = 0.5. As the Ta⁵⁺ content increases in the binary solid-solutions, the E-field-induced irreversible antiferroelectric → ferroelectric (AFE → FE) transition becomes reversible at x ≥ 0.2, giving rise to double-polarization hysteresis; the key E-fields triggering both irreversible and reversible transitions (E_F) increase in general. In particular, the E-field-induced FE phase at x = 0.15 is unstable upon unloading E-field to zero, which can return to AFE phase with time lapse. At x = 0.5, the Curie temperature (T_C) of AFE shifts to below room temperature, but E-field-induced reversible transition is still observed, which results in a nonlinear polarization with the lowest hysteresis and contributes to the largest energy-storage density. This transition is not due to the AFE ↔ FE transition but rather to the order ↔ disorder behavior of polar clusters or/and nanoregions within nonpolar Pbnm structure matrix.     

Effects in Surface Free Energy of Sputter-Deposited VNx Films

Vanadium nitride (VN _x ) thin films have attracted much attention for semiconductor integrated circuit (IC) packaging molding dies, and forming tools due to their excellent hardness and, thermal stability. VN _x thin films with VN_0.45, VN_0.83, VN_1.22, VN_1.73, VN_2.06 were prepared using a radio frequency (RF) sputter technique. The experimental results showed that the contact angle at 20°C increases with increasing nitrogen content of the VN _x films, to 101.4° corresponding to VN_1.73 and then decreased. In addition, the contact angles decreased with increasing surface temperature, because an increase of the surface temperature disrupts the hydrogen bonds between water and the films and the water gradually vaporizes. The total surface fee energy (SFE) at 20°C decreased with nitrogen content of the VN _x films to 29.8 mN/m (VN_1.73) and then increased. This is because a larger contact angle means weaker hydrogen bonding which results in a lower SFE. The polar SFE component had the same trend as the total SFE, but the dispersive SFE component had the opposite trend. The polar SFE component is also lower than the dispersive SFE component. This is because hydrogen bonds are polar. The total SFE, dispersive SFE and polar SFE of the VN _x films all decrease with increasing surface temperature. This is because with increasing temperature, water evaporates from the surface, disrupting hydrogen bonds and hence increasing surface entropy. The film roughness has an obvious effect on the SFE and there is tendency for the SFE to increase with increasing film surface roughness. As a result the SFE and surface roughness can be expressed in terms of a simple ratio function.     

Ferroelectric and magnetic properties in (1−x)BiFeO3–x(0.5CaTiO3–0.5SmFeO3) ceramics

Multiferroic ceramics were prepared and characterized in (1?x)BiFeO₃–x(0.5CaTiO₃–0.5SmFeO₃) system by a standard solid‐state reaction process. The structure evolution was investigated by X‐ray diffraction and Raman spectrum analyses. The refinement results confirmed the different phase assemblages with varying amounts of polar rhombohedral R3c and nonpolar orthorhombic Pbnm as a function of the substitution content. In the compositions range of 0.2≤x≤0.5, polar R3c and nonpolar Pbnm coexisted, which was referred to polar‐to‐nonpolar morphotropic phase boundary (MPB). According to the dielectric and DSC analysis results, the ceramics with x≤0.2 changed to diffused ferroelectric, and the ferroelectric properties were enhanced significantly. Two dielectric relaxations were detected in the temperature range of 200‐300 K and 500‐700 K, respectively. The high‐temperature dielectric relaxation was attributed to the grain‐boundary effects. While the low temperature dielectric relaxation obtained in the samples with x=0.3‐0.5 was related to the charge transfer between Fe²⁺ and Fe³⁺. The magnetic hysteresis loops measured at different temperature indicated the enhanced magnetic properties in the present ceramics, which could be attributed to the suppressed cycloidal spin magnetic structure by Ti ions. In addition, the rare‐earth Sm spin moments might also affect the magnetic properties at relatively lower temperature.     

Correlation of the solubility of volatile liquids in molten polymers

The solubility of volatile liquids at infinite dilution (i.e., in the Henry's law region) in poly(vinyl acetate) (PVAc) and polystyrene (PS) at elevated temperatures has been correlated by plotting ln(1/K_p) against (T_c/T)², where T_c is the critical temperature of the solute and K_p is Henry's constant at temperature T and a total pressure of approximately at 1 atm, defined as P₁ = K_pV₁⁰, where P₁ is the partial pressure of the solute in the vapor phase and V₁⁰ is the solubility (cm³ solute per g polymer at 273.2 K and 1 atm). For this correlation, we have used experimental data available in the literature for 16 solutes covering 81 data points for PVAc and 17 solutes covering 82 data points for PS. We have calculated values of 1/K_p from the literature data reported in terms of the retention volume V_g⁰, weight-fraction Henry's constant H₁, and activity coefficient at infinite dilution Ω₁^∞. We have made the following observations: (1) for PVAc, ln(1/K_p) = ?1.564 + B(T_c/T)²; and (2) for PS, ln(1/K_p) = ?2.028 + B(T_c/T)². In both cases, we found that values of B, the slope in the ln(1/K_p) versus (T_c/T)² plots, vary with the acentric factor ω of the solutes. It has been found that, in both PVAc and PS at the same value of ω, values of B for slightly polar aromatic solutes are larger than those for nonpolar aliphatic solutes. Further, in PS at the same value of ω, values of B are smaller for strongly polar solutes than for slightly polar solutes, whereas in PVAc the opposite trend holds. This observation may be interpreted as that the solubility of strongly polar solutes in a polar polymer (e.g., PVAc) is greater than that of slightly polar and nonpolar solutes, whereas the solubility of strongly polar solutes in a nonpolar polymer (e.g., PS) is less than that of slightly polar solutes but greater than that of nonpolar solutes. The dependence of B on ω, observed in this investigation, is at variance with the correlations reported by Tseng, Lloyd, and Ward for PVAc and by Stiel and Harnish for PS.     

Studies on the surface free energy and surface structure of PTFE film treated with low temperature plasma

The surface free energy and surface structure of poly(tetrafluoroethylene) (PTFE) film treated with low temperature plasma in O₂, Ar, He, H₂, NH₃, and CH₄ gases are studied. The contact angles of the samples were measured, and the critical surface tension γ_c (Zisman) and γ_c (max) were determined on the basis of the Zisman's plots. Furthermore, the values of nonpolar dispersion force γ^a_s, dipole force γ^b_s, and hydrogen bonding force γ^c_s to the surface tensions for the plasma-treated samples were evaluated by the extended Fowkes equation. Mainly because of the contribution of polar force, the surface free energy and surface wettability of PTFE film which was treated with H₂, He, NH₃, Ar, and CH₄ for a short time increased greatly. Electron spectroscopy for chemical analysis (ESCA) shows that the reason was the decrease of fluorine and the increase of oxygen or nitrogen polar functional group on the surface of PTFE. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1733–1739, 1997     

Encapsulation and controlled release of fragrances from functionalized porous metal–organic frameworks

In the fragrance and perfume industry, the encapsulation and controlled release of fragrance is important to appeal to consumers and promote the quality of products. Here, we demonstrate that porous metal–organic frameworks (MOFs) can effectively encapsulate and release fragrant molecules in a controlled manner. The incorporation of functional groups into MOFs can improve the adsorption and release behavior of fragrant molecules. We find that polar ester-type fragrances exhibit higher adsorption on polar hydroxyl-functionalized MOF [UiO-66-(OH)₂] than on nonpolar MOF (UiO-66), while nonpolar terpenoid-type fragrances show no adsorption difference between these two MOFs. The release profiles show that UiO-66-(OH)₂ can prolong the release of polar fragrances compared with nonpolar fragrances. Both the experimental results and computer molecular modeling demonstrate that the hydroxyl groups in UiO-66-(OH)₂ can form strong hydrogen binding with different ester fragrances. The releasing kinetics indicates that pore diffusion is the rate-limiting step of fragrance release from MOFs. © 2018 American Institute of Chemical Engineers AIChE J, 65: 491–499, 2019     

Structure-property relationships in thermoplastic elastomers: I. Segmented polyether-polyurethanes

Segmented poly(ether-b-urethanes) have been synthesized with 2000 MW polypropylene oxide coupled with diisocyanates and diol type chain extenders. The diisocyanates used were symmetric rigid 4, 4′-diphenylmethane diisocyanate (MDI), linear aliphatic hexamethylene diisocyanate (HDI), and unsymmetric rigid toluene-2, 4-diisocyanate (TDI). The chain extenders were symmetric N, N′-bis(2-hydroxyethyl) terephthalamide (BT) and N, N′-bis(2-hydroxyethyl)-hydroquinone (BH) unsymmetric N, N′-bis(2-hydroxyethyl)isophthalamide, and linear aliphatic 1, 4-butanediol (B). Hard segment contents ranged from 20 to 40 wt percent. The thermal behavior of these materials is consistent with phase separation into separate hard and soft domains, In order of increasing temperature above the soft segment T_g, there are transitions which occur in the regions ?56 to ?36°C (T_a), 70 to 90°C (T_b), and 138 to 168°C (T_m). The former is probably associated with soft segment change from a viscoelastic to an elastomeric state. Values of T_a are ～ ?51 C and ?56°C for the MDI-BT and HDI-BT polymers, respectively, and are independent of hard segment content. Microscopy showed that the former polymers have spherulitic morphology, so these materials have good microphase separation and exhibit crosslinked elastomeric properties. The TDI-BT or BI and MDI-B polyurethane have composition-independent T_a values of ?41 and ?36°C, respectively. These materials probably have considerable “domain-bound-ary-mixing”. At low hard segment content the MDI-B polymers behave as non-crosslinked elastomers. Only the MDI-BI polymers have _Ta values, which are strongly affected by composition, increasing in magnitude with increasing of hard segment content. This is interpreted as significant “mixing-in-domains” and is supported by morphology observed by microscopy. The next higher transition, T_b, probably involves dissociation of interdomain hydrogen bonding. In the case of the MDI-BT polyurethanes, the spherulites associated with the hard domains had disappeared at 141°C and the few small spherulites in the MDI-BI polymers disappeared at 130°C. The T_b values are 70, 83 to 90, and 100°C for the MDI-B, HDI-BT, and HDI-BI polymers, respectively. The melting transitions occurred between 138 to 168°C for the various polyurethanes except for the MDI-BT systems which decompose before melting. Thermal decomposition is a two-stage process. Hard segments decompose between 200 and 300°C. The initial decomposition temperatures are lowered in the presence of strong acid. Soft segments decompose at higher temperatures. The mechanical properties of the MDI-BI polyurethanes are charateristic of crosslinked elastomer, the results of which will be presented in a subsequent paper.     

Viscoelastic properties and coating performance of acrylic copolymers crosslinked with melamine resin

For 8 carboxy and hydroxy functional acrylic copolymers crosslinked with melamine resin, glass transition temperature (T_g), molecular weight of chain segments between crosslinked point (M_c), and polymer-solvent interaction parameters (χ_g ) were determined by dynamic mechanical measurements and swelling measurements. T_g increases and M_c decreases with the increase of hydroxyl value and the molecular weight of acrylic copolymers. T_g decreases and M_c increases with the increase of alkyl chain length of acrylate in acrylic copolymers. The film hardness, T_g and polarity of methyl methacrylate (MMA) containing acrylic-melamine-cured films are higher than those of styrene-containing acrylic-melamine-cured films, but both films are almost the same in the degree of crosslinking (maximum loss tangent, tan δ_max, and M_c). T_g increases and M_c decreases with the increase of melamine resin content for acrylic-melamine coatings. The cured film consists of the acrylic-melamine segments and the melamine-melamine segments at crosslinking points. The carboxy group enhances the crosslinking reactions at low temperatures. All films crosslinked have single glass transition temperatures and broad damping peaks, which show good compatibility. The values of χ_g of acrylic copolymer-melamine films in polar and nonpolar solvents depend on the polarity of acrylic composition and the degree of crosslinking. χ_g values of carboxy functional acrylic-melamine film in any solvents are smaller than that of carboxy and hydroxy functional acrylic-melamine film. χ_g values of MMA-containing acrylic-melamine film in polar solvents are smaller than those of styrene-containing acrylic-melamine film, but χ_g values of MMA-containing acrylic-melamine film in nonpolar solvents are larger than those of styrene-containing acrylic-melamine film. χ_g values of acrylic-melamine film in polar and nonpolar solvents increase with the increase of alkyl chain length of acrylate. The χ_g values of acrylic-melamine coatings in toluene are less than 0.3 and smaller than those of alkyd coatings.     

Molecule transfer mechanism in two-dimensional heterostructured lamellar membranes: The effects of dissolution and diffusion

Two-dimensional lamellar membranes are promising for efficient molecule transfer, while the underlying transfer mechanism is rarely elucidated. Herein, heterostructured nanosheets are prepared by self-assembling small-sized hydrophilic cyanuric acid melamine and hydrophobic g-C₃N₄ nanosheets. Resultant lamellar membranes show comparable affinity to polar and nonpolar solvents, allowing them to dissolve on membrane surface and diffuse through membrane channels. Results demonstrate that for lamellar membranes with distinct wettability, the permeance difference for polar solvents is originated from dissolution and diffusion processes, while that for nonpolar solvents is stemmed from dissolution process. Accordingly, corresponding equations which are suitable for heterostructured lamellar membranes are established. Importantly, polar solvents are induced to form ordered arrangement in hydrophilic nanodomains and then maintain the ordered state in hydrophobic nanodomains, affording a low-resistance transfer and high acetonitrile permeance of 1025 L m⁻² h⁻¹ bar⁻¹. In contrast, nonpolar solvents with disordered arrangement exhibit lower permeance than that of polar ones.     

Structural and mechanical properties of polybutadiene-containing polyurethanes

A series of segmented polyurethanes based on hydroxylterminated polybutadienes (HTPBD) and their hydrogenated derivatives (HYPBD) has been synthesized. Thermal, mechanical, and spectroscopic studies were carried out over a wide temperature range to elucidate the structure-property relationships existing in these polymers. Both thermal and dynamic mechanical response showed a soft segment T_g at ?74°C for the unsaturated polyurethanes and at ?69°C for the hydrogenated samples. In addition, two hard segment transitions are observed by differential scanning calorimetry (DSC) at 40 and 75°C and a softening region by thermal mechanical analysis (TMA) at 190°C. The low T_g, very close to that of the free HTPBD and HYPBD and independent of hard segment content, indicated that these polymers were well phase separated. Results of infrared analysis revealed that at room temperature, 90-95 percent of the urethane N-H groups formed hydrogen bonds. Since hydrogen bonding resides only within the hard segment domain in these butadiene-containing polyurethanes the extent of H-bonding served as additional evidence for nearly complete phase segregation. From dynamic mechanical studies, the plateau modulus above the soft segment T_g and stress-strain behavior depended upon the concentration of hard segments. A slight increase in the modulus, a moderate increase in stress (σ_b), and decrease in elongation accompanied a higher hard segment content. The thermal and mechanical response of these polyurethanes appears to be consistent with behavior observed for other phase segregated systems. Variations in behavior resulting from hydrogenation of the precursor prepolymer are discussed.     

Properties of polyisobutylene-polyurethane block copolymers: I. Macroglycols from ozonolysis of isobutylene-isoprene copolymer

The properties of a series of polyisobutylene (PIB) based polyurethanes were studied and compared to those reported in the literature for polyether, polyester, and polybutadiene-based polyurethanes. Good phase separation was reflected in the invariance of the soft segment T_n with increasing hard segment content. Increasing hard segment content resulted in larger domains, higher modulus and lower ultimate elongation. The modulus above the soft segment T_n was higher than that previously reported for polyurethanes of similar hard segment contant; improved phase separation and short contour lengths of the PIB chains were cited as possible causes of this behavior. Stress-strain data indicated a change from isolated to interconnected domain morphology with incerasing hard segment contant. Generally similar trends were seen for all types of urethanes. The overall properties of polybutadiene polyurethanes were closest to those of the polyisobutylene polyurethanes studied. The properties of both of these systems were suggested to suffer from significant synthesis problems in urethane formation due to the incompatibility of the nonpolar hydrocarbon soft segment and the polar diol chain extender. Preliminary environmental tests indicated that polyisobutylene based materials exhibit improved hydrolytic stability and reduced moisture permeability compared to polyether and polyester polyurethanes and greater oxidative stability compared to polybutadiene based materials.     

Influence of magnesium on dielectric properties of Ca9–xMgxBi(VO4)7 ceramics

Solid solution of Ca_9‐xMg_xBi(VO₄)₇ in powder and ceramic forms are obtained by solid‐state reactions. Details of their crystal structures are determined for x = 0.25 and x = 0.5 by synchrotron radiation diffraction and the Rietveld method. The refinement has confirmed that Mg²⁺ is replacing Ca²⁺ in M5 position of a polar (S.G. R3c) β‐Ca₃(PO₄)₂‐type structure. Thermal analysis, dielectric and second harmonic generation experiments in broad temperature regions have proved this polar structure is formed for 0 ≤ x ≤ 0.7. Magnesium for calcium substitution enhances optical nonlinear activity of Ca_9‐xMg_xBi(VO₄)₇ in 0 < x ≤ 0.5. Two phase transitions have been found, one of which from polar to centrosymmetric phase is accompanied by dielectric constant peak of ferroelectric type. The other is upper on temperature, marked with smaller dielectric anomaly, and goes between 2 centrosymmetric phases. Temperatures of the phase transition only slightly depend on x, the first being near 1050 K, the second near 1100 K. Electric conductivity quickly rises with temperature in the polar phase. At higher temperature it changes according to the Arrhenius law with small activation energy, E_a ~ 0.7 eV for bulk conductivity and E_gb ~ 2.0‐2.5 eV for grain boundary conductivity. The analysis of bulk and grain boundary conductivities agrees with Ca²⁺‐ion fast transport in ceramics. The bulk conductivity slowly decreases with magnesium content, the grain boundary conductivity does not notably depend on the composition.     

Thermal and mechanical properties of solution polymerized segmented polyurethanes with butadiene soft segments

A series of HTPBD containing polyurethanes of high molecular weight have been synthesized in solution. The value of the soft segment T_g is very close to that of the free HTPBD and independent of hard segment content indicating complete or very nearly complete phase segregation. Since the hard segments of TDI/BDO are amorphous, the driving force for phase segregation must arise from the large degree of incompatibility between the polar hard segment and nonpolar soft segment. Furthermore, in these samples there is also no opportunity for hydrogen bonding between hard and soft segments to enhance compatibility.The values of the hard segment glass transition increase with the average hard segment length following a Fox-Flory type relationship. In contrast to the segment T_g observed in bulk polymerized samples, only a single hard segment T_g occurred in the present study. This indicates that the double T_g behaviour is a result of the heterogeneous nature of the bulk polymerization.With increasing hard segment content, the properties vary from soft to rigid elastomers, and rubber roughened plastics. This variation in properties is caused by changes in the sample morphology which depends upon the relative fractions of hard and soft segments. Mechanical properties show marked improvement over the corresponding bulk polymerized samples. Unlike polyester and polyether urethanes, these materials evidence no change in the soft segment T_g following thermal treatment and no effect of thermal history on the mechanical properties.     

Orientation‐Dependence of Thermal Depolarization and Phase Development in Bi1/2Na1/2TiO3‐BaTiO3 Single Crystals

The direction‐dependence of pyroelectric properties of (1 ? x)Bi_1/2Na_1/2TiO₃ ? xBaTiO₃ (BNT ? 100xBT) is investigated, using single crystal samples with well‐defined orientations for x = 0.036 and x = 0.063. The results are compared with those of temperature‐dependent measurements of the ferroelectric and dielectric hysteresis. The depolarization temperature T_d of each crystal composition is found to depend on crystal orientation, a fact that is explained by differences in the stability of respective domain configurations. A rationalization is offered for the observation that T_d differs from the ferroelectric‐relaxor transition temperature, depending on orientation. The hysteresis curves of BNT ? 3.6BT are typical for a rhombohedral system with a ferroelectric‐relaxor transition, with polarization reversal close to T_d occurring in a multistep process that includes decay of ferroelectric domains into polar nanoregions and re‐formation of domains. BNT ? 6.3BT, a composition in the region of the morphotropic phase boundary, shows the same feature, but additionally is characterized by a field‐induced transition between rhombohedral and tetragonal symmetry. This combination results in an effective piezoelectric coefficient of pm/V.     

Dielectric and ferroelectric properties of the sol‐gel–derived Zr‐doped Ba0.7Sr0.3TiO3 polycrystalline ceramic systems

Ba_0.7Sr_0.3Zr_xTi_1?xO₃ (BSZT; where x=0.02, 0.04, 0.06, 0.08, 0.1) ceramics were processed through a sol‐gel method at 1450°C for 6 h. All the samples showed a diffuse phase transition which might be due to the presence of polar nanoregions, those associated with the composition inhomogeneity in the BSZT ceramics. The sample with x=0.02 exhibited a dielectric constant (?=23714) which successively decreased with increasing x up to 8569 for the sample with x=0.1 around T_c measured at 10 kHz. Ceramic samples showed a ferroelectric hysteresis behavior similar to relaxor materials.     

Surface tension versus barrier property for fluorinated surfaces

The barrier property of fluorinated surfaces was compared to the surface tension measurements. A relationship between barrier property and the solvent's surface tension was developed. However, other properties of both the solvent and the polymer contribute to barrier property. The surface tension of the polymer surface was separated into nonpolar, polar, and hydrogen bonding forces. By estimating the % γ of various solvent mixtures, the % γ_S^D was estimated for the polymer surface.     

Enhanced mechanical properties of poly(lactic acid) composites with ultrathin nanosheets of MXene modified by stearic acid

MXene modified by stearic acid (Ti₃C₂T_x-g-SA) is incorporated into poly(lactic acid) (PLA) matrix to prepare Ti₃C₂T_x-g-SA/PLA composites. The effects of Ti₃C₂T_x-g-SA to pure PLA are investigated, including crystallization, mechanical, and thermal properties. Fourier transform infrared spectroscopy and X-ray diffraction analyses confirm that Ti₃C₂T_x interlayer is successfully intercalated by SA, and the interlayer spacing of Ti₃C₂T_x is increased. Differential scanning calorimetry illustrates that the cold crystallization enthalpy (ΔH_cc), melting enthalpy (ΔH_m), and crystallinity (X_c) of Ti₃C₂T_x-g-SA/PLA composites are improved by the plasticization and heterogeneous nucleation effect of Ti₃C₂T_x-g-SA. Specially, the Ti₃C₂T_x-g-SA/PLA composites exhibit excellent mechanical properties at an appropriate content of the Ti₃C₂T_x-g-SA. Compared with pure PLA, the elongation at break of the Ti₃C₂T_x-g-SA/PLA composite is increased 5.9-fold (up to 131.6%) when only containing 0.5 wt % Ti₃C₂T_x-g-SA. Besides, the Ti₃C₂T_x-g-SA/PLA composites exhibit good thermal stability in the low loading (lower than 1 wt %) of Ti₃C₂T_x-g-SA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48621.