Molecular characterization of Ulex europaeus biochar obtained from laboratory heat treatment experiments – A pyrolysis–GC/MS study

Gorse species (Ulex sp.) are ubiquitous in the shrublands of NW Spain and have the potential to become key players in an integral biofuel/biochar program in NW Spain. Here we present molecular characterization (using pyrolysis–GC/MS) of a biochar “thermosequence” obtained by laboratory heating of Ulex europaeus wood in a muffle furnace between 200 and 600 °C (T_CHAR). Low temperature chars (T_CHAR ≤ 350 °C) produced significant amounts of pyrolysis products of which the precursor biopolymer could be recognized, while high-temperature chars (T_CHAR ≥ 400 °C) produced mainly phenols and monocyclic and polycyclic aromatic hydrocarbons, which are not specific for any biopolymer. Carbohydrate could hardly be recognized at T_CHAR ≥ 350 °C. The thermal rearrangement of polyphenols, mainly lignin, was reflected in more detail (1) C₃-side chain shortening and probably depolymerization (T_CHAR 200–350 °C), (2) demethoxylation of syringyl and probably also some guaiacyl lignin (T_CHAR 300–400 °C), (3) elimination of virtually all remaining methoxyl groups (T_CHAR 350–400 °C), through dehydroxylation and demethoxylation, (4) almost complete dehydroxylation of lignin and other biopolymers (T_CHAR 400–500 °C), (5) progressive condensation into polyaromatic structures (T_CHAR 300–500 °C) and (6) partial elimination of alkyl bridges between (poly)aromatic moieties (T_CHAR 450–500 °C). These results were supported by Fourier transform infrared spectroscopy (FTIR) of the same samples. We conclude that pyrolysis–GC/MS can be used as a rapid molecular screening method of gorse-derived biochar. Molecular properties elucidation is an essential part of predicting the stability and agronomical behavior of gorse-derived biochar after future implementation in soils.     

Thermodynamic interactions of water-soluble homopolymers and double-hydrophilic diblock copolymer

Thermodynamic interaction parameters of water-soluble poly[2-(dimethylamino)ethyl methacrylate] (DMA) and poly[2-(N-morpholino)ethyl methacrylate] (MEMA) homopolymers and their diblock copolymer (DMA–MEMA) were investigated at the temperatures above their glass-transition temperatures (T_g) by inverse gas chromatography (IGC) method. Sorption thermodynamic parameters of some aliphatic, alicyclic and aromatic hydrocarbons, weight fraction activity coefficients, Flory–Huggins interaction parameters, and solubility parameters for hydrocarbons and polymers were calculated. It was observed that sorption thermodynamic parameters on (co)polymers depend on the molecular structures of hydrocarbons. Evaluating both the calculated values of the weight fraction activity coefficients and Flory–Huggins interaction parameters, the solving ability of the hydrocarbons for DMA, MEMA homopolymers, and DMA–MEMA diblock copolymer decreased in the following sequence: Aromatic > alicyclic > aliphatic hydrocarbons.     

Effect of compressed CO2 on crystallization and melting behavior of isotactic polypropylene

Compressed gases such as CO₂ above their critical temperatures provide a highly tunable technique that has been shown to induce changes in phase behavior, crystallization kinetics and morphology of the polymers. Gas induced plasticization of the polymer matrix has been studied in a large number of polymers such as polystyrene, and poly(ethylene terephathalate). The knowledge of polymer–gas interactions is fundamental to the study of phenomena such as solubility and diffusivity of gases in polymers, dilation of polymers and in the development of applications such as foams and barrier materials.In this paper, we describe the interactions of compressed CO₂ with isotactic polypropylene (PP). Crystallization of various PPs in presence of compressed CO₂ was evaluated using a high pressure differential scanning calorimeter (HPDSC). CO₂ plasticized the polymer matrix and decreased the crystallization temperature, T_c by ∼8 °C for PP at a pressure of 650 psi CO₂. The decrease as a function of pressure was −0.173 °C/bar and did not change with the molecular architecture of PP. Both crystallization kinetics and melting behavior are evaluated.Since solubility and diffusivity are important thermodynamic parameters that establish the intrinsic gas transport characteristics in a polymer, solubility of CO₂ in PP was measured using a high-pressure electrobalance and compared with cross-linked polyethylene. At 50 °C, solubility followed Henry’s law and at a pressure of 200 psi about 1% CO₂ dissolved in PP. Similar solubility was achieved in PE at a pressure of 160 psi. Higher solubility of CO₂ in PE is attributed to its lower crystallinity and lower T_g, than PP. Diffusion coefficients were calculated from the sorption kinetics using a Fickian transport model. Diffusivity was independent of pressure and PE showed higher diffusivity than PP. Preliminary foaming studies carried out using a batch process indicate that both PP and PE can be foamed from the solid state to form microcellular foams. Cell size and cell density were ∼10 μm and 10⁸ cells/cm³, respectively in PE. Differences in morphology between the foams for these polymers are attributed to the differences in diffusivity.     

Influence of thermal treatment on the glass transition temperature of thermosetting epoxy laminate

The influence of accelerated thermal treatment of thermosetting epoxy laminate on its glass transition temperature was studied. Lamplex^® FR-4 glass fibre-reinforced epoxy laminate (used for printed circuit board manufacturing) was used in these experiments. The composite was exposed to thermal treatments at temperatures ranging from 170 °C to 200 °C for times ranging from 10 to 480 h. The glass transition temperature (T_g) was analysed via dynamic mechanical analysis (DMA). It has been proven that the glass transition temperature rapidly decreases in reaction to thermal stress. The obtained T_g data were used for Arrhenius plots for different critical temperatures (T_g-crit. = 105–120 °C). From their slopes (?E_a/R), the activation energy of the thermal degradation process was calculated as 75.5 kJ/mol. In addition to this main relaxation mechanism, DMA also recorded one smaller relaxation process in the most aged samples. Microscopic analysis of the sample structure showed the presence of pronounced small regions of degradation both on the surface and in the inner structure, which are probably the causes of microscopic delamination and the smaller relaxation process.     

Determining crystal growth rate-type of curves in glasses by differential thermal analysis

A crystal growth rate vs. temperature (U vs. T)-type of curve for a Li₂O.2SiO₂ glass was determined up to a temperature of 690 °C using a differential thermal analysis (DTA) method. As determined from this (U vs. T)-type of curve, the temperature corresponding to the onset of crystal growth was 570±3 °C which is in excellent agreement with the same value determined by the conventional method. The complete range of temperature where crystal growth can occur and the temperature (T_max) where the crystal growth rate is a maximum for this glass could not be determined. It is concluded that for temperatures <T_max, the DTA method can delineate only a small, initial portion of the (U vs. T)-type of curve, where the crystal growth rate is sufficiently low so that the glass does not totally crystallize after the required (for at least 5 min) isothermal heat treatment at these temperatures. For temperatures >T_max, the curve cannot be determined by the DTA method if the temperature for isothermal heat treatment is approached by heating the glass from room temperature. For determining the curve for temperatures >T_max, the desired temperature (>T_max) for isothermal heat treatment of the glass is suggested to be approached from the melting temperature of the glass.     

Synthesis,characterization and thermal studies of new polyhydrazides and its poly-1,3,4-oxadiazoles based on dihydro-9,10-ethanoanthracene in the main chain

New interesting class of new polyhydrazides having inherent viscosities in the range 0.45–0.71 dI/g were prepared by polymerizing a series of diacid chlorides, e.g., sebacoyl, isophthaloyl or terphthaloyl with 9,10-dihydro-9,10-ethanoanthracene-11,12-dihydrazide I in polar aprotic solvent and by the low-temperature polycondensation technique. In order to characterize the polymers, a model compound II was synthesized from I and benzoyl chloride. All the hydrazide polymers are semi crystalline in nature and are readily soluble in various polar solvents such as N-methyl pyrrolidine (NMP) and dimethylsulfoxide (DMSO). Their T_gs were recorded in the range of 78–95 °C and could be thermally dehydrated into the corresponding polyoxadiazoles in the region of 310–20 °C, as evidenced by the DTA thermograms. The oxadiazole polymers showed a dramatically decreased in solubility and higher T_g when compared to their respective hydrazide prepolymers. The morphology of polyhydrazide V was examined by SEM.     

Synthesis and characterization of LiCo3/5Mn2/5VO4 ceramics

Dielectric and a.c. conductivity properties of LiCo_3/5Mn_2/5VO₄ ceramic are investigated. This compound is prepared by solution-based chemical method and the formation is checked by X-ray diffraction (XRD) study. XRD analysis at room temperature shows an orthorhombic phase. Frequency dependence of dielectric constant (?_r) at different temperatures shows a dispersive behavior at low frequencies. Temperature dependence of ?_r at different frequencies indicates the transition temperature (T_c) = 235 °C, 245 °C, 257 °C and 265 °C with (?_r)_max. ～3689, 1373, 750 and 386 for 10, 50, 100 and 200 kHz respectively. A.c. conductivity analysis indicates that electrical conduction in the material is a thermally activated process.     

A calorimetric and thermodynamic investigation of A2[(UO2)2(MoO4)O2] compounds with A = K and Rb and calculated phase relations in the system (K2MoO4 + UO3 + H2O)

A calorimetric and thermodynamic investigation of two alkali-metal uranyl molybdates with general composition A₂[(UO₂)₂(MoO₄)O₂], where A = K and Rb, was performed. Both phases were synthesized by solid-state sintering of a mixture of potassium or rubidium nitrate, molybdenum (VI) oxide and gamma-uranium (VI) oxide at high temperatures. The synthetic products were characterised by X-ray powder diffraction and X-ray fluorescence methods. The enthalpy of formation of K₂[(UO₂)₂(MoO₄)O₂] was determined using HF-solution calorimetry giving Δ_fH° (T = 298 K, K₂[(UO₂)₂(MoO₄)O₂], cr) = −(4018 ± 8) kJ · mol⁻¹. The low-temperature heat capacity, С_р°, was measured using adiabatic calorimetry from T = (7 to 335) K for K₂[(UO₂)₂(MoO₄)O₂] and from T = (7 to 326) K for Rb₂[(UO₂)₂(MoO₄)O₂]. Using these С_р° values, the third law entropy at T = 298.15 K, S°, is calculated as (374 ± 1) J · K⁻¹ · mol⁻¹ for K₂[(UO₂)₂(MoO₄)O₂] and (390 ± 1) J · K⁻¹ · mol⁻¹ for Rb₂[(UO₂)₂(MoO₄)O₂]. These new experimental results, together with literature data, are used to calculate the Gibbs energy of formation, Δ_fG°, for both phases giving: Δ_fG° (T = 298 K, K₂[(UO₂)₂(MoO₄)O₂], cr) = (−3747 ± 8) kJ · mol⁻¹ and Δ_fG° (T = 298 K, Rb₂[(UO₂)₂(MoO₄)], cr) = −3736 ± 5 kJ · mol⁻¹. Smoothed С_р°(Т) values between 0 K and 320 K are presented, along with values for S° and the functions [H°(T) − H°(0)] and [G°(T) − H°(0)], for both phases. The stability behaviour of various solid phases and solution complexes in the (K₂MoO₄ + UO₃ + H₂O) system with and without CO₂ at T = 298 K was investigated by thermodynamic model calculations using the Gibbs energy minimisation approach.     

Synthesis and second-order nonlinear optical properties of a crosslinkable functionalized hyperbranched polymer

A new implementation of copper-free thermal Huisgen 1,3-dipolar crosslinking reaction into a high T_g hyperbranched polyimide polymer in order to stabilize the electro-optic (EO) activity of second-order non linear materials is reported. Towards this goal, two different synthetic approaches were explored. The first strategy is based on the post-functionalization of the polymer with mixtures of DR1 azido derivative and propargylic alcohol, whereas, the second consists in the preparation of two complementary functionalized hyperbranched polymers that are mixed just before the preparation of films. Materials exhibit good second-order nonlinear optical coefficients (d₃₃) close to 30 pm/V at the fundamental wavelength of 1064 nm. Moreover, the thermal stability of the NLO properties of these materials reaches temperatures as high as 150 °C, and probably higher. This represents the highest thermal stability of crosslinkable EO polymers based on the crosslinking Huisgen reaction.     

Colorless poly(ester imide)s derived from hydrogenated trimellitic anhydride

Tetracarboxylic dianhydrides were synthesized from hydrogenated trimellitic anhydride (HTA) and some diols to obtain novel poly(ester imide)s (PEsIs). The HTA-derived tetracarboxylic dianhydrides showed much higher reactivity with various diamines than conventional cycloaliphatic tetracarboxylic dianhydrides and led to PEsI precursors with high molecular weights (M_w). The results can be explained in terms of a spacer effect. The PEsI films were essentially colorless regardless of diol and diamine components owing to inhibited charge-transfer interactions. The HTA-derived PEsIs also exhibited excellent combined properties: relatively high glass transition temperatures (T_g), relatively low water absorption (W_A), and relatively low dielectric constants. The outstanding processability (thermoplasticity and solubility) observed for the HTA-derived PEsIs was discussed on the basis of a non-planar/bent structure at the HTA-based imide units. The use of a fluorene-containing diol component was effective for enhancing T_g’s by restricted internal rotation and for reducing W_A by a decreased imide group content. On the other hand, the use of 4,4′-biphenol as another diol gave rise to a prominent toughening effect without sacrificing other target properties. One of the HTA-derived PEsI systems can be a promising candidate as plastic substrates because of its excellent combined properties: a high T_g close to 300 °C, high optical transparency, significant toughness (elongation at break > 100%), and good thermo- and solution-processability.     

Polyimide-derived carbon nanofiber membranes as anodes for high-performance flexible lithium ion batteries

Heteroatoms-doped carbon nanofiber membranes with flexible features were prepared by electrospinning with heterocyclic polyimide (PI) structures containing biphenyl and pyrimidine rings. The products with optimized treatment could achieve 695 mAh/g at 0.1 A/g and retain 245 mAh/g at 1.5 A/g after 300 cycles when used as anode for Li-ion batteries.     

Synthesis,thermal and mechanical properties of benzocyclobutene-functionalized siloxane thermosets with different geometric structures

A series of benzocyclobutene-functionalized siloxane thermosets were prepared to investigate the relationship between the monomer’s chemical structure and the properties of the corresponding polymer. Monomer 1,1,3,3-tetramethyl-1,3-bis[2′-(4′-benzocyclobutenyl)]vinyldisiloxane (DVS-BCB) and 1,3,5,7-tetramethyl-1,3,5,7-tetra[2′-(4′-benzocyclobutenyl)]vinylcyclotetrasiloxane (CYC-BCB) were synthesized by Heck reaction. Copolymer Poly(DVS-BCB-co-POSS) was obtained through incorporating octavinyl-T8-silsesquioxane (Vinyl-POSS) into DVS-BCB matrix via Diels–Alder reaction. The oligomers, P-DVS-BCB, P-CYC-BCB and P-Poly(DVS-BCB-co-POSS), were obtained by refluxing the mesitylene solution of the BCB monomers at the BCB ring opening temperature. The BCB monomers and oligomers showed a similar curing behavior with an exothermic peak temperature near 260 °C. The curing kinetic parameters, the apparent activation energy (E_a), the frequency factor (A) and the reaction order (n), were obtained by non-isothermal DSC method. The BCB polymers possessed good thermal stability (T_d > 450 °C in N₂). Due to the highly crosslinked network structure, CYC-BCB polymer exhibited higher glass transition temperature, higher modulus and lower coefficient of thermal expansion than DVS-BCB and Poly(DVS-BCB-co-POSS) polymers. Moreover, the BCB polymers also demonstrated low dielectric constants (<2.8 at 1 MHz) and low water absorptions. The films prepared from the BCB oligomer solution showed a well planarization (root-mean-square roughness <0.5 nm).     

Synthesis and properties of polyimides containing <Emphasis Type="Italic">N</Emphasis>-substituted benzimidazole rings

A series of novel benzimidazole-containing aromatic polyimides with precise structures in high yields were synthesized by the catalyst-free nucleophilic substitution polycondensation of 4,4’-bis(4-fluorophthalimido) diphenyl ether with different molar ratios of 1,4-bis(2-benzimidazolyl) benzene to 4,4’-dihydroxydiphenyl sulfone via a C–N/C–O coupling reaction process. The reaction was carried out at 210°C in the presence of anhydrous potassium carbonate. The structures of the resulting polymers were characterized by means of FTIR, ¹H NMR spectroscopy, and elemental analysis, and the results were largely consistent with the proposed structure. DSC and TG measurements showed that the polymers had high glass transition temperatures (T_g > 215°C), good thermostability, and high decomposition temperatures (T_d5% > 456°C). These novel polymers also showed easy solubility. In addition, the obtained films have good optical transparency, and the mechanical properties exhibited tension strength of 48.2–74.8 MPa and tensile moduli of 1.3–1.9 GPa without any stretching.     

Assembling of a novel 3D Ag(I)-MOFs with mixed ligands tactics: Syntheses,crystal structure and catalytic degradation of nitrophenol

A novel 3D Ag(I)-MOFs, [Ag₂(H₃ddcba)(dpp)₂] (1), which features pcu (4¹²·6³) topology were successfully synthesized. Complex 1 exhibits predominant catalytic activity towards the degradation of o-nitrophenol (2-NP), m-nitrophenol (3-NP) and p-nitrophenol (4-NP) in aqueous solution.     

Structural phase stability and magnetism in Co2FeO4 spinel oxide

We report a correlation between structural phase stability and magnetic properties of Co₂FeO₄ spinel oxide. We employed mechanical alloying and subsequent annealing to obtain the desired samples. The particle size of the samples changes from 25 nm to 45 nm. The structural phase separation of samples, except sample annealed at 900 °C, into Co-rich and Fe-rich spinel phase has been examined from XRD spectrum, SEM picture, along with EDX spectrum, and magnetic measurements. The present study indicated the ferrimagnetic character of Co₂FeO₄, irrespective of structural phase stability. The observation of mixed ferrimagnetic phases, associated with two Curie temperatures at T_C1 and T_C2 (>T_C1), respectively, provides the additional support of the splitting of single cubic spinel phase in Co₂FeO₄ spinel oxide.     

Structure,nonstoichiometry and magnetic properties of the perovskites Sr1−xCaxMnO3−δ

The structural, thermal and magnetic properties of the perovskite-type alkaline-earth manganites of the series Sr_1−xCa_xMnO_3−δ (0⩽x⩽1) were investigated. SrMnO_3−δ forms a hexagonal perovskite lattice and shows a first-order transformation to a highly defective cubic high-temperature modification. By substituting Ca for Sr (x>0.25) the hexagonal perovskite is suppressed and a cubic (or orthorhombic) lattice becomes stabilized for all temperatures. For x=0.5 and 0.75 cubic perovskites with a large nonstoichiometry (e.g., δ=0.25 for x=0.5) are obtained at 1400 °C. The defective perovskites are prepared by either quenching from high temperature or by cooling in an inert atmosphere. The oxygen vacancies are easily filled by subsequent reoxidation at low temperature (400–600 °C) and stoichiometric samples are obtained. Orthorhombic perovskites are formed at T⩽1200 °C with the nonstoichiometry δ increasing with increasing temperature (e.g., δ=0.06 at 1000 °C and δ=0.14 at 1200 °C for x=0.5). Slow cooling in air results in almost complete reoxidation (δ=0). CaMnO_3−δ is an orthorhombic perovskite with a large range of nonstoichiometry (0⩽δ⩽0.30). The cubic to hexagonal phase transformation of the Sr-rich samples is accompanied by a large expansion of the lattice that is reduced by Ca substitution. The Ca/Sr-manganites are antiferromagnets with T_N of 170 K for x=0.5 and δ=0.02 and 120 K for x=1 and δ=0.05.     

Critical properties of some aliphatic symmetrical ethers

The critical temperatures T_c and the critical pressures p_c of dihexyl, dioctyl, and didecyl ethers have been measured. According to the measurements, the coordinates of the critical points are T_c = (665 ± 7) K, p_c = (1.44 ± 0.04) MPa for dihexyl ether, T_c = (723 ± 7) K, p_c = (1.19 ± 0.04) MPa for dioctyl ether, and T_c = (768 ± 8) K, p_c = (1.03 ± 0.03) MPa for didecyl ether. All the ethers studied degrade chemically at near-critical temperatures. A pulse-heating method applicable to measuring the critical properties of thermally unstable compounds has been used. The times from the beginning of a heating pulse to the moment of reaching the critical temperature were from 0.06 to 0.46 ms. The short residence times provide little decomposition of the substances in the course of the experiments. The critical properties of the ethers investigated in this work have been discussed together with those of methyl to butyl ethers. The experimental critical constants of the ethers have been compared with those estimated by the group-contribution methods of Wilson and Jasperson and Marrero and Gani. The Wilson/Jasperson method provides a better estimation of the critical temperatures and pressures of simple aliphatic ethers in comparison with the Marrero/Gani method if reliable normal boiling temperatures are used in the method of Wilson and Jasperson.     

Structure development during isothermal crystallisation of high-density polyethylene: Synchrotron small-angle X-ray scattering study

Isothermal melt crystallisation in high-density polyethylene (HDPE) was studied using the time-resolved SAXS method with synchrotron radiation over a wide range of crystallisation temperatures. The SAXS profile was analysed by an interface distribution function, g₁(r), which is a superposition of three contributions associated with the size distributions of crystalline (L_C) and amorphous (L_A) layers and a distribution of long period (LP). The morphological parameters extracted from the g₁(r) functions show that the lamellar thickness increases with time, obeying a logarithmic time dependence. The time evolution of L_C observed for the sample crystallised at 122 °C leads to the conclusion that crystallisation proceeds according to the mechanism of thickening growth. For samples crystallised at lower temperatures (116 °C and 118 °C), the lamellar thickening mechanism has been observed. The rate of lamellar thickening in these cases is much lower than that at 122 °C. At 40 °C, thickening of the crystalline layer does not occur. The interface distribution functions were deconvoluted, and the relative standard deviation σ_C/L_C obtained in this way is an additional parameter that is varied during crystallisation and can be used for analysis of this process. Time-dependent changes in the σ_C/L_C at large supercooling (T_C=40 °C) indicates that L_C presents a broad distribution in which the relative standard deviation increases with time. At lower supercooling (T_C=122 °C), L_C shows a much sharper distribution. In this case, the relative standard deviation decreases with time.     

Influence of iron on the synthesis and stability of yttrium silicate apatite

The stability of yttrium silicate apatite has been investigated by studying the influence of iron as a “stabilising cation” and also by using different synthesis routes. The formation of apatite in samples has been followed by X-ray diffraction and by ²⁹Si MAS NMR spectroscopy. The apatite phase appears to be stable at high temperatures (≈1700 °C) especially when heated in a nitrogen atmosphere; it can also occur in a metastable state when heated in air at lower temperatures; ≈1600 °C if prepared from a Y₂O₃SiO₂ mixture or in the range 950 °C <T< 1150 °C if synthesised by the sol–gel process. Longer heat-treatments result in its decomposition into Y₂Si₂O₇ and Y₂SiO₅. Iron appears to have two roles depending on the temperature; it stabilises the apatite phase at high temperatures when produced by the sol–gel route and catalyses the decomposition of sol–gel derived apatite at low temperatures.     

Studies on thermoplastic polyurethanes based on new diphenylethane-derivative diols. I. Synthesis and characterization of nonsegmented polyurethanes from HDI and MDI

New aliphatic–aromatic α,ω-diols containing sulfur in aliphatic chain: 4,4′-(ethane-1,2-diyl)bis(benzenethioethanol) [EBTE], 4,4′-(ethane-1,2-diyl)bis(benzenethiopropanol) [EBTP], 4,4′-(ethane-1,2-diyl)bis(benzenethiohexanol) [EBTH], 4,4′-(ethane-1,2-diyl)bis(benzenethiodecanol) [EBTD], and 4,4′-(ethane-1,2-diyl)bis(benzenethioundecanol) [EBTU] were prepared by the condensation reaction of 4,4′-(ethane-1,2-diyl)bis(benzenethiol) with suitable halogen alcohols in aqueous sodium hydroxide solution. Thermoplastic nonsegmented polyurethanes containing sulfide linkages were synthesized from these diols, and hexane-1,6-diyl diisocyanate (HDI) or 4,4′-methylenediphenyl diisocyanate (MDI) by solution and melt polymerization. The reaction was carried out at 1:1 or 1.05:1 molar ratios of isocyanate and hydroxy groups in the presence of dibutyltin dilaurate as a catalyst.The structures of the diols were determined by using elemental analysis, FTIR and ¹H NMR spectroscopy, and X-ray diffraction analysis. Thermal characteristics of the diols were determined by using differential scanning calorimetry (DSC). The polymers were studied to describe their structures and physicochemical, thermal (by DSC and thermogravimetric analysis) and tensile properties as well as Shore A/D hardness.All the polyurethanes possessed partially crystalline structures. Their melting temperatures were in the range of 94–179 °C (HDI) and 105–207 °C (MDI). The MDI-based polyurethanes showed higher tensile strengths, up to ∼50 MPa.