Polymers from Fatty Acids: Poly(ω-hydroxyl tetradecanoic acid) Synthesis and Physico-Mechanical Studies

Abstract

This Article describes the synthesis and physicomechanical properties of bioplastics prepared from methyl ω-hydroxytetradecanoic acid (Me-ω-OHC14), a new monomer available by a fermentation process using an engineered Candida tropicalis strain. Melt-condensation experiments were conducted using titanium tetraisopropoxide (Ti[OiPr](4)) as a catalyst in a two-stage polymerization (2 h at 200 °C under N(2), 4 h at 220 °C under 0.1 mmHg). Poly(ω-hydroxytetradecanoate), P(ω-OHC14), M(w), determined by SEC-MALLS, increased from 53K to 110K as the Ti(OiPr)(4) concentration increased from 50 to 300 ppm. By varying the polymerization conditions (catalyst concentration, reaction time, second-stage reaction temperature) a series of P(ω-OHC14) samples were prepared with M(w) values from 53K to 140K. The synthesized polyesters with M(w) ranging from 53K to 140K were subjected to characterization by DSC, TGA, DMTA, and tensile testing. Influences of P(ω-OHC14) molecular weight, melting point, and enthalpies of melting/crystallization on material tensile properties were explored. Cold-drawing tensile tests at room temperature for P(ω-OHC14) with M(w) 53K-78K showed a brittle-to-ductile transition. In contrast, P(ω-OHC14) with M(w) 53K undergoes brittle fracture. Increasing P(ω-OHC14) M(w) above 78K resulted in a strain-hardening phenomena and tough properties with elongation at break ~700% and true tensile strength of ~50 MPa. Comparisons between high density polyethylene and P(ω-OHC14) mechanical and thermal properties as a function of their respective molecular weights are discussed.

Polyhydroxyester Films Obtained by Non-Catalyzed Melt-Polycondensation of Natural Occurring Fatty Polyhydroxyacids

“…Within the series, crystalline poly HPA is the stiffest and displays a brittle fracture at quite low strain. If compared to values reported for the analogous poly ω-hydroxyl tetradecanoic acid (Liu et al, 2011), it can be deduced that this behavior is likely caused by a low molecular weight polymerization and by partial amorphization, as indicated by the broad peak around 20° in Figure 4. In this sense, self-polycondensation of HPA under reduced pressure is more efficient and yields a higher molecular weight polyester.…”

“…In every case, ester formation is clearly stated from the carbonyl 13 C MAS-NMR peak around 174 ppm (Garbow and Stark, 1990;Zlotnik-Mazori and Stark, 1998;Ahmed et al, 2003;Pandey et al, 2010;Arrieta-Baez et al, 2011;Liu et al, 2011) (Figure 2) and the characteristic FTIR ν(C=O) around 1730 cm −1 and ν(OC-O-C) bands at 1240 and 1170 cm −1 (Bellamy, 1975) (Figure 3). A detailed analysis of obtained polyesters is given below:…”

“…FTIR data, (Figure 3), confirm the formation of the polyester by the characteristic peaks at 1732 and 1169 cm −1 (Liu et al, 2011) FigUre 2 | solid state 13 c Mas-nMr spectra of polyesters. For clarity, the intensity of the 50-200 ppm region is multiplied by a factor of 3.…”

“…The filtrate was neutralized with HCl 1N and extracted with diethyl ether. The solid contains about 82% (w/w) of 10(9),16-dihydroxyhexadecanoic acids and minor amounts of other diacids and hydroxyacids (Baker and Holloway, 1970;del Río and Hatcher, 1998;Kosma et al, 2010). The chemical structure of monomers and polyester nomenclature used along this article are summarized in (Figure 1).…”

“…Chemically, cutin can be described as an amorphous polymeric network of ester bonded C16 and C18 polyhydroxylated fatty acids (Baker and Holloway, 1970;Kolattukudy, 1981;Walton, 1990). Thus, the reaction involved is an esterification between the carboxylic acid and the alcohol groups that is typically performed by polycondensation in an organic media using an acidic surfactant as a promoter or a metallic catalyst (Bawn and Huglin, 1962;Saam, 1998;HerediaGuerrero et al, 2009;Liu et al, 2011;Zhang et al, 2011). However, to avoid the use of organic solvents as well as aromatic and heavy metal catalysts jeopardizing the non-toxicity of the final product, we have used the direct, non-catalyzed synthesis from molten precursors in air.…”