Here
we investigate the relationship between thermomechanical properties
and chemical structure of well-characterized lignin-based epoxy resins.
For this purpose, technical lignins from eucalyptus and spruce, obtained
from the Kraft process, were used. The choice of lignins was based
on the expected differences in molecular structure. The lignins were
then refined by solvent fractionation, and three fractions with comparable
molecular weights were selected to reduce effects of molar mass on
the properties of the final thermoset resins. Consequently, any differences
in thermomechanical properties are expected to correlate with molecular
structure differences between the lignins. Oxirane moieties were selectively
introduced to the refined fractions, and the resulting lignin epoxides
were subsequently cross-linked with two commercially available polyether
diamines (Mn = 2000 and 400) to obtain lignin-based epoxy resins.
Molecular-scale characterization of the refined lignins and their
derivatives were performed by
31
P NMR, 2D-NMR, and DSC
methods to obtain the detailed chemical structure of original and
derivatized lignins. The thermosets were studied by DSC, DMA, and
tensile tests and demonstrated diverse thermomechanical properties
attributed to structural components in lignin and selected amine cross-linker.
An epoxy resin with a lignin content of 66% showed a Tg of 79 °C
from DMA, Young’s modulus of 1.7 GPa, tensile strength of 66
MPa, and strain to failure of 8%. The effect of molecular lignin structure
on thermomechanical properties was analyzed, finding significant differences
between the rigid guaiacyl units in spruce lignin compared with sinapyl
units in eucalyptus lignin. The methodology points toward rational
design of molecularly tailored lignin-based thermosets.
A new method for the synthesis of polyesters that combines the chemical recycling of poly(ethylene terephthalate) (PET) with the use of monomers derived from renewable resources, such as isosorbide and succinic acid, has been developed. A kinetic study has been performed in order to determine the best catalyst for PET depolymerisation with isosorbide and for the subsequent polycondensation of PET oligomers with succinic acid. Using the correct amounts of isosorbide and succinic acid it is possible to obtain polymers which well fit the properties (glass transition temperature and end-group composition) necessary for powder coating applications. The coating produced using this new environmentally friendly approach presents applicative properties similar, and in some cases superior, to those of a commercial coating obtained from non-renewable resources.
A new and sustainable pathway for the synthesis of polyesters and copolyesters derived from vanillic acid is reported. The one-pot procedure does not require either solvents or purification steps. New bio-based crystalline copolymers with tunable thermal properties are obtained.
The action of FeCl(3) on 3-(alkylsulfanyl)thiophenes (3-(alkylthio)thiophenes) leads to the one-step formation of regioregular alpha-conjugated oligothiophenes, from trimer to octamer, depending on the solvent used and on the length of the alkyl chain. The regiochemistry of these oligomers is characterized by one inner head-to-head linkage between adjacent rings and by a variable number of lateral head-to-tail junctions. The reaction of ferric chloride with the head-to-head and head-to-tail bis(methylsulfanyl)-2,2'-bithiophenes gives the corresponding tetramers, while the reaction with the tail-to-tail counterpart affords a high molecular weight insoluble material. With the aid of theoretical calculations, these results are interpreted on the basis of the joint effects of the orienting power of the substituents and of the stability of the radical cations formed during the oxidative process.
Weatherable semicrystalline polyesters based on 1,4-cyclohexanedimethanol, 1,4-cyclohexanedicarboxylic acid (CHDA) or dimethyl 1,4-cyclohexane dicarboxylate (DMCD) can be prepared under normal melt-phase conditions, using titanium tetrabutoxide as catalyst. The effect of monomer ratio, reaction temperature and catalyst loading on the final polymer properties was studied. Under the proper polymerization conditions, poly(1,4-cyclohexylenedimethylene-1,4-cyclohexanedicarboxylate) polymers with high molecular weight can be obtained. During polymerization, isomerization can occur towards the thermodynamically stable cis-trans ratio of 34-66 mol%. Carboxylic acid end groups can catalyze the isomerization and therefore the polymerization is more critical starting from CHDA rather than DMCD. Moreover, temperature control becomes a key factor to avoid or to limit isomerization. The study of the isomerization of the different monomers permitted a better understanding of the isomerization and therefore of the polymerization process
Summary: Copolyesters of terephthalic acid with bis(hydroxyethyl ether) of bisphenol A (BHEEB) in different molar ratios have been synthesized by reactive blending from terephthalate polyesters and by melt polycondensation from the monomers. By this way, bisphenol A groups were inserted in the polyester chains with the aim to obtain polyesters with improved mechanical properties. The insertion of the BHEEB into the polyester backbone is quantitative and does not give rise to side reactions. These copolyesters can be obtained by the chemical recycling of commercial polymers; indeed BHEEB can be synthesized by chemical recycling of bisphenol A polycarbonate and may be incorporated in the polyester by reactive blending with recycled terephthalate polyesters. A new method for BHEEB synthesis by chemical recycling of PC is also presented.Glass transition temperature (Tg) as function of BHEEB content for copolyesters prepared by reactive blending BHEEB with terephthalate polyesters.magnified imageGlass transition temperature (Tg) as function of BHEEB content for copolyesters prepared by reactive blending BHEEB with terephthalate polyesters.
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