Natural
terpenes such as linalool (L), geraniol (G), and geranyl
acetate (GA), from 10 to 20 wt %, were compounded with poly(3-hydroxybutyrate)
(PHB) to assess the influence of the content of these biobased molecules
on the structural and mechanical properties of PHB. Differential scanning
calorimetry (DSC) measurements showed a decrease of T
g from 8.5 °C to −13 °C, showing the
plasticization effect of the terpenes. This effect is correlated with
the decrease of the crystallinity degree from 57 to 36%. Moreover,
tensile tests were conducted on PHB-containing terpenic plasticizers.
The increase of the elongation at the break of the plasticized PHB
over 650% combined with a decrease of the Young’s modulus with
regard to pure PHB were obtained in the presence of 20 wt % of geranyl
acetate. Dynamical mechanical analysis also revealed that the use
of terpenes as additives promoted the decrease of E′ and the
glass transition temperature. The effect is more pronounced with geranyl
acetate due to the presence of the segment bearing an ester group
that increases free volume and molecular mobility. Among the different
plasticizers used here, the addition of geranyl acetate is an attractive
way to obtain soft PHB from renewable additives.
By using a combination of bio-based monomers, sunflower oil (S) and monoterperne, the β-myrcene (M), or a sesquiterpene, the β-farnesene (F), a series of novel networks S x M 100−x and S x F 100−x with different compositions were prepared by a green chemistry route, without any solvent or catalyst, using the Diels−Alder reaction at 100 °C to obtain branched materials. The presence of oxygen during this process is responsible of the formation of oxidation products that are characterized by Fourier transform infrared (FTIR) and Raman spectroscopies, a swell as X-ray photoelectron spectroscopy (XPS) analysis. Materials prepared with 100% terpenes (PM 100 and PF 100 ) are very hard and brittle, whereas materials prepared from vegetable oil (PS 100 ) are tearable. The properties of S x M 100−x and S x F 100−x are closely linked to the composition and, in particular, to the content of terpenes. It is observed that, by increasing the proportion of terpenes from 0 to 80 wt %, there was a marked increase in the glass-transition temperature (T g ) values, from 13.8 °C to 58.2 °C for S 20 F 80 networks and up to 92.3 °C for S 20 M 80 networks. Although the S 20 M 80 network presents higher tensile modulus (97 MPa) and tensile strength (8.8 MPa), the S 50 M 50 network is the more promising material, combining high resistance and good flexibility. These resulting materials exhibited remarkable swelling capacity when they were immersed in eugenol, which is an interesting antibacterial compound. The release profile indicated a Fickian diffusion model with the release of 90% of eugenol in 30 days, providing interesting antibacterial properties to the materials.
Biobased semi-interpenetrating polymer
networks (semi-IPNs) in
which poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s,
PHBHV, are embedded in a tridimensional network were developed to
improve the mechanical properties of polyesters. Semi-IPNs are obtained
by cross-linking sunflower oil (SO) and trimethylolpropane tris(3-mercaptopropionate)
(TriSH) using a photoactivated thiol–ene reaction in the presence
of 2,2′-dimethoxy-2-phenyl acetophenone. The SO-TriSH contents
in the network varied from 20 to 45% wt. Homogeneous semi-IPNs containing
from 20 to 40% of SO-TriSH content exhibited lower glass temperature
from 4 to −15 °C, higher strain at break values from 7
to 150%, and better thermal stability than those of pristine PHBHV.
This reveals an improvement of the deformability of PHBHV due to the
plasticization domains by the SO-TriSH domains. The fact that a fraction
of the interpenetrating networks follows Fox equation, which is usually
verified by well-mixed plasticizer/polymer systems, could be a positive
signature of an interpenetrating effect between reticulated SO-TriSH
and PHBHV chains. Those properties were achieved without degrading
the intrinsic crystalline structure of PHBHV as demonstrated by WAXS
measurements.
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