Aliphatic-aromatic Polyesters Research Articles

Fragmentation and Mineralization of a Compostable Aromatic–Aliphatic Polyester during Industrial Composting

Fragmentation and Mineralization of a Compostable Aromatic–Aliphatic Polyester during Industrial Composting

Synthesis and properties of biodegradable aliphatic–aromatic polyesters derived from 4‐hydroxybenzaldehyde

AbstractA novel biphenyl monomer, diethyl 6,6′‐dimethoxy‐[1,1′‐bipheny]‐3,3′‐dicarboxylate (DDBD), was synthesized from 4‐hydroxybenzaldehyde, a phenolic compound derived from lignin. A series of polyesters were prepared by polycondensation of the biphenyl monomer with hydroquinone bis(2‐hydroxyethyl) ether and aliphatic diacids via a two‐step melt polycondensation method. It was shown that the properties of the polyesters can be tuned by varying the length and the structure of the spacer in the aliphatic diacid monomers. Structure–property relations for these materials were investigated by Fourier‐transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. GPC analysis showed that the weight‐average molecular weight (Mw) of the samples varied from 4.2–5.0 × 104 g/mol, while thermal analysis yielded Tg values of 51–120°C, and 5% decomposition temperatures (Td,5%) of 327–389°C. All the samples exhibited a high yield strength (56–87 MPa). After 30 weeks of degradation in soil, the copolyesters had mass losses of up to 4.4%, and an investigation of the ecotoxicity of the copolyesters with Eisenia fetida yielded a survival rate of over 80% after 14 days for the different copolyesters, suggesting low toxicity in the environment. Overall, these copolyesters have good properties and would be suitable to replace petroleum‐based commercial poly(ethylene terephthalate) packaging materials.

Enzymatically catalyzed furan-based copolyesters containing dilinoleic diol as a building block.

A more environmentally friendly method for creating sustainable alternatives to traditional aromatic-aliphatic polyesters is a valuable step towards resource-efficiency optimization. A library of furan-based block copolymers was synthesized via temperature-varied two-step polycondensation reaction in diphenyl ether using Candida antarctica lipase B (CAL-B) as a biocatalyst where dimethyl 2,5-furandicarboxylate (DMFDCA), α,ω-aliphatic linear diols (α,ω-ALD), and bio-based dilinoleic diol (DLD) were used as the starting materials. Nuclear magnetic spectroscopy (1H and 13C NMR), Fourier transform spectroscopy (FTIR) and size exclusion chromatography (SEC) were used to analyze the resulting copolymers. Additionally, crystallization behavior and thermal properties were studied using X-ray diffraction (XRD), digital holographic microscopy (DHM), and differential scanning microscopy (DSC). Finally, oxygen transmission rates (OTR) and dynamic mechanical analysis (DMTA) of furan-based copolyesters indicated their potential for medical packaging.

Aliphatic-Aromatic Polyesters from Naturally Occurring Sinapic Acid through Acyclic-Diene Metathesis Polymerization in Bulk and Green Solvent Cyrene

Green synthesis of renewable alternatives to fossil fuel-based (macro)molecules/polymers is more than ever a necessity. We recently developed a sustainable pathway to produce 6-hydroxy-5,7-dimethoxy-2-naphthoic acid (DMNA), which resembles the fossil-derived 6-hydroxy-2-naphthoic acid, from sinapic acid. To investigate the potential of DMNA as a building block for polymer syntheses, three novel DMNA-derived α,ω-dienes (M1–M3) were synthesized and engaged in acyclic-diene metathesis (ADMET) polymerization in a three-step study to prepare renewable aliphatic-aromatic polyesters (P1–P3). The first step aimed to evaluate the activity of seven commercial metathesis catalysts for the solvent-free ADMET polymerization of M3. Although most of the studied catalysts exhibited good reactivity, the second-generation Hoveyda–Grubbs catalyst (C4) proved the best. The second step was then started by varying the catalyst loading and testing M1 and M2 toward ADMET polymerization. Aliphatic-aromatic polyesters with a number-average molecular weight (Mn) up to 19.4 kDa (Đ = 1.88) were obtained. Furthermore, the results showed that the properties can be finely tuned depending on the monomer and catalyst loading. Thermal analysis demonstrated that the glass transition temperature (Tg) and the temperature at which 5% of the mass is lost (Td5%) varied depending on the alkene chain length. A general thermal trend was established: Tg(P1) > Tg(P2) > Tg(P3) and Td5%(P1) < Td5%(P2) < Td5%(P3). The third step of the ADMET study was to evaluate the tolerance of M1–M3 and C4 toward Cyrene, a green and high boiling point solvent derived from cellulose. The results revealed that Cyrene merits further investigation as a “general” non-toxic solvent for ADMET polymerization of other monomers, particularly those with high melting points.

Stretchable and Fast Composting Polyester Films with High-Performance Oxygen Barrier

This work presents one of the fastest composting aliphatic–aromatic polyesters with a good balance of mechanical and barrier properties, making it a sustainable alternative for low-density polyethylene in packaging. The polyesters (PBxBDMyS) are prepared by melt polycondensation of 1,4-butanediol (B), 1,4-benzenedimethanol (BDM), and succinic acid (S). One composition exhibited a tensile strength of 20 ± 2 MPa, a modulus of 150 ± 8 MPa, and a very high elongation at break of 581 ± 46%. The low oxygen transmission rate (152 cm3·m–2·day–1·bar–1) measured at 65% relative humidity and 23 °C confirms excellent barrier performance. A 3 μm water-borne nanocomposite coating of glycol chitosan and sodium fluorohectorite further reduced the gas permeability to a value of 0.75 cm3·m–2·day–1·atm–1, which is competitive with materials suitable for demanding packaging applications such as poly(vinylidene chloride) while maintaining good mechanical properties and high stretchability. After studying the enzyme-catalyzed hydrolysis under controlled conditions, the full fragmentation, assimilation, and mineralization in thermophilic, aerobic composting could be confirmed in less than 5 weeks using a combination of different analytical methods. The mechanism of degradation was proven to be bulk degradation.

Impact of enzymatically synthesized aliphatic–aromatic polyesters with increased hydroxyl group content on coating properties

AbstractNowadays, coating systems have to fulfill a wide range of requirements. In addition to mechanical properties such as hardness and elasticity, resistance and weatherability, specifically corrosion or chemical resistance are also important. Increasing attention is also being paid to points such as the use of sustainable reactants or the energy optimization of synthesis processes.1 The use of enzymes in the synthetic processes offers two main advantages: firstly, reaction temperatures can be significantly reduced, for example in the production of polyesters, and as a result and a major advantage, certain functional groups can be selectively retained during the reaction.2,3 Thus, for example, aromatic hydroxyl groups can be obtained, while aliphatic groups are esterified.4,5 This allows the preparation of polyesters that do not only have terminal OH groups, but hydroxyl groups within the chain that can act as additional crosslinking points during network formation or as adhesion-promoting groups.6,7 In this work, the influence of such an aliphatic–aromatic polyester, produced enzymatically at low temperatures, on the coating properties is investigated when using different hardener components. Coating formulations were created, and the required OH functionality and the hydroxyl number of the enzymatic polyester have been calculated by using two different, independent methods. Besides the development of guide formulations, the unique mechanical properties of coatings based on the enzymatic polyester were studied. In addition to comparative analysis of network densities, the coatings were also investigated by IR spectroscopy in order to assess the network formation reaction spectroscopically. It can be shown that additional OH groups in the polyester chain increase the network density, but this is not at the expense of elasticity. Thus, enzymatically produced polyesters combine the advantages of low reaction temperatures during production with a unique property profile due to aliphatic and aromatic moieties as well as the partial preservation of OH groups within the chain.

Enzymatic synthesis of novel aromatic‐aliphatic polyesters with increased hydroxyl group density

Polyesters with pendant hydroxyl groups are attractive materials which offer additional functionalization points in the polymer chain. In contrast to chemical polycondensation, lipase regioselectivity enables the synthesis of these materials as certain hydroxyl groups remain unaffected during the enzymatic process. In this study, a combination of synthesis development and reactor design was used for the enzymatic synthesis of an aliphatic-aromatic polyester with two different classes of pendant hydroxyl groups. Using 2,6-bishydroxy(methyl)-p-cresol as diol in lipase catalyzed polycondensation with adipic acid required the addition of hexane diol as third monomer for polycondensation to take place. Reaction conditions were explored in order to identify the preferred reaction conditions for the incorporation of the aromatic diol and the enhancement of the hydroxyl group density. Post-polymerization with glycerol at low temperature integrated additional aliphatic hydroxyl groups, reduced the polydispersity and increased the end group functionality. A new material with aromatic building blocks and boosted polymer chain reactivity was obtained, which is suggested to find application in various areas of material development from coatings to adhesives.

Enhanced degradation and gas barrier of PBAT through composition design of aliphatic units

Aliphatic–aromatic copolyesters are indispensable in degradable plastics, but their properties are limited by low strength and modulus, and slow degradation rates in natural environment. Herein, we report a novel molecular design method to prepare poly(butylene adipate–co–diglycolate–co–terephthalate)(PBADT) copolyesters. In detail, the aromatic unit is fixed at 50% molar content of butylene terephthalate (BT) units, while the aliphatic units are consisted of butylene adipate (BA) and butylene diglycolate (BD) units. The PBADT copolyesters have melting temperatures higher than 130 °C and manifest rapid crystallization, high elastic modulus (>129 MPa) and satisfied ductile tensile behavior (>770%). Their gas barrier performance and hydrophilicity all increase with increasing BD units. Compared with PBAT, faster hydrolysis and seawater degradation are observed, which is explained by the more hydrophilic structure of diglycolate. This work provides insights and direction for the development of high-performance yet environmentally degradable alternatives to conventional biodegradable aliphatic–aromatic polyesters.

Biobased High-Performance Aromatic-Aliphatic Polyesters with Complete Recyclability.

The development of high-performance recyclable polymers represents a circular plastics economy to address the urgent issues of plastic sustainability. Herein, we design a series of biobased seven-membered-ring esters containing aromatic and aliphatic moieties. Ring-opening polymerization studies showed that they readily polymerize with excellent activity (TOF up to 2.1 × 105 h-1) at room temperature and produce polymers with high molecular weight (Mn up to 438 kg/mol). The variety of functionalities allows us to investigate the substitution effect on polymerizability/recyclability of monomers and properties of polymers (such as Tgs from -1 to 79 °C). Remarkably, a stereocomplexed P(M2) exhibited significantly increased Tm and crystallization rate. More importantly, product P(M)s were capable of depolymerizing into their monomers in solution or bulk with high efficiency, thus establishing their circular life cycle.

Enzymatic synthesis of biobased polyesters utilizing aromatic diols as the rigid component

In the present work, the biocatalyzed synthesis of a series of aromatic-aliphatic polyesters based on the aliphatic diesters dimethyl succinate, dimethyl adipate and dimethyl sebacate and the aromatic diols 2,5-bis(hydroxymethyl)furan, 3,4-bis(hydroxymethyl)furan and 2,6-pyridinedimethanol were investigated. A similar series of polyesters based on the petroleum-based 1,3-benzenedimethanol, 1,4-benzenedimethanol and 1,4-benzenediethanol were also synthesized for comparison. Data show that the enzymatic syntheses were successful starting from all diols, with the obtained polymers having isolated yields between 67 and over 90%, number average molecular weights between 3000 Da and 5000 Da and degree of polymerization (DP) of 6–18 (based on the used aliphatic diesters and aromatic diols) when polymerized in diphenyl ether as solvent. Only using 3,4-bis(hydroxymethyl)furan as the diol led to shorter oligomers with isolated yields around 50% and DPs of 3–5. DSC and TGA thermal analyses show clear correlation between polymer crystallinity and aliphatic carbon chain length of the diester.

Sustainable Aromatic Aliphatic Polyesters and Polyurethanes Prepared from Vanillin-Derived Diols via Green Catalysis.

The design and preparation of polymers by using biobased chemicals is regarded as an important strategy towards a sustainable polymer chemistry. Herein, two aromatic diols, 4-(hydroxymethyl)-2-methoxyphenol and 2-(4-(hydroxymethyl)-2-methoxyphenoxy)ethanol, have been prepared in good yields through the direct reduction of vanillin and hydroxyethylated vanillin (4-(2-hydroxyethoxy)-3-methoxybenzaldehyde) using NaBH4, respectively. The diols were submitted to traditional polycondensation and polyaddition with acyl chlorides and diisocyanatos, and serials of new polyesters and polyurethanes were prepared in high yields with moderate molecular weight ranging from 17,000 to 40,000 g mol−1. Their structures were characterized by 1H NMR, 13C NMR and FTIR, and their thermal properties were studied by TGA and differential scanning calorimetry (DSC), indicating that the as-prepared polyesters and polyurethanes have Tg in the range of 16.2 to 81.2 °C and 11.6 to 80.4 °C, respectively.

Kinetic, thermal, structural and degradation studies on the effect of meta-substituted aromatic-aliphatic polyesters built through ring-opening polymerisation

Here we synthesise and characterise novel aromatic-aliphatic polyesters based on poly(2-(2-hydroxyethoxy)benzoate) (P2HEB). The polyesters were a product of the ring-opening polymerisation of their respective substituted benzodioxepinones catalysed by an aluminium salen catalyst. The electronic effects of the substituents on the polymerisation and thermal behaviour were investigated. The polymerisation and depolymerisation kinetics showed faster rates for electron withdrawing groups with selective depolymerisation back to their cyclic monomers in 10 min at 110 °C. The thermal characterisation showed varying glass transition temperatures from 29.7 °C to 60.7 °C with electron withdrawing groups exhibiting higher values. An increase in the melting temperatures and the thermal degradation activation energies of the polyesters were also observed. The crystal structures of the polyesters corresponded to semi-crystalline polyesters. The polymerisation and thermal behaviour of these novel aromatic-aliphatic polyesters can be tuned through manipulation of the meta-positioned R group, thus expanding the scope of catalytically degradable, functionalized aromatic-aliphatic polyesters that are accessible through ring-opening polymerisation.

Thermal Field-Flow Fractionation for Characterization of Architecture in Hyperbranched Aromatic-Aliphatic Polyesters with Controlled Branching.

Thermal field-flow fractionation (ThFFF) was used to characterize the architecture of aromatic-aliphatic polyesters with varying degrees of branching. Thermal diffusion and Soret coefficients (DT and ST, respectively) provide a novel route to polymer architecture analysis. This paper demonstrates an innovative strategy to extract architecture information from the physicochemical separation parameters embedded in ThFFF retention times without explicit separation of linear and branched samples. A Soret contraction factor (g″), defined as the ratio of the ST of a branched polymer to the ST of a molecular weight equivalent linear analogue, is introduced as a metric to indicate degree of branching (DB). This approach circumvents several challenges associated with the analysis of high molar mass polymers with a high degree of branching. The g″ value is shown to be proportional to the degree of branching for linear (DB, 0%), gradually branched (DB, <50%), hyperbranched (DB, 50%), and pseudodendritic (DB, 100%) polyesters allowing the establishment of architecture calibration curves. Furthermore, positive log(g″) values (∼0.2) at low molar mass are attributed to cyclic subpopulations. This work demonstrates the usefulness of the Soret contraction factor for statistically and hyperbranched polymer systems and its sensitivity to cyclic polymers.

Fiber formation and properties of polyester/lignin blends

ABSTRACTThermotropic liquid crystalline polyesters with varied chemical structure are synthesized by melt transesterification polycondensation. They are employed as matrix for blends with lignin materials to obtain melt‐spinnable precursors for carbon fibers. The lignin samples are carefully purified by fractionation, enzymatic removal of reducing sugars, and subsequent modification of the terminal OH groups. Effective melt blending is achieved with liquid‐crystalline aromatic–aliphatic polyesters having melting ranges that match the softening temperature of the lignin fractions, which is necessary to prevent thermal decomposition of the lignin. Polyester/lignin blends are partially compatibilized, phase‐separated materials. The polyester/lignin materials are melt‐spun successfully. The fiber properties depend on the lignin purification process. X‐ray scattering reveals that orientation in lignin‐containing fibers is maintained. First experiments show that the fibers can be converted successfully to carbon fibers by thermal annealing procedures. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48257.

Enzymatic synthesis of lignin derivable pyridine based polyesters for the substitution of petroleum derived plastics

Following concerns over increasing global plastic pollution, interest in the production and characterization of bio-based and biodegradable alternatives is rising. In the present work, the synthesis of a series of fully bio-based alternatives based on 2,4-, 2,5-, and 2,6-pyridinedicarboxylic acid-derived polymers produced via enzymatic catalysis are reported. A similar series of aromatic-aliphatic polyesters based on diethyl-2,5-furandicarboxylate and of the petroleum-based diethyl terephthalate and diethyl isophthalate were also synthesized. Here we show that the enzymatic synthesis starting from 2,4-diethyl pyridinedicarboxylate leads to the best polymers in terms of molecular weights (Mn = 14.3 and Mw of 32.1 kDa when combined with 1,8-octanediol) when polymerized in diphenyl ether. Polymerization in solventless conditions were also successful leading to the synthesis of bio-based oligoesters that can be further functionalized. DSC analysis show a clear similarity in the thermal behavior between 2,4-diethyl pyridinedicarboxylate and diethyl isophthalate (amorphous polymers) and between 2,5-diethyl pyridinedicarboxylate and diethyl terephthalate (crystalline polymers).

Synthesis of Aromatic–Aliphatic Polyesters by Enzymatic Ring Opening Polymerization of Cyclic Oligoesters and their Cyclodepolymerization for a Circular Economy

Cyclic oligomers of hexamethylene furanoate and hexamethylene terephthalate were obtained from 1,6-hexanediol and the corresponding methyl esters using Candida antarctica lipase B (CALB) enzyme catalyst. HPLC, MALDI-TOF MS, and NMR analyses showed that mixtures composed from cyclic dimer up to heptamer were obtained almost quantitatively. Subsequently, these cycles were polymerized by ring opening polymerization (ROP) mediated by CALB to obtain semicrystalline polymers. In addition, we demonstrated that the polymers obtained from the ROP process could be transformed into cyclic oligomers in high yields using enzymatic cyclodepolymerization, thereby recycling the polymer in a circular biosynthetic path.

Photochemical Transformation of Poly(butylene adipate- co-terephthalate) and Its Effects on Enzymatic Hydrolyzability.

Biodegradable polyesters are being increasingly used to replace conventional, nondegradable polymers in agricultural applications such as plastic film for mulching. For many of these applications, poly(butylene adipate- co-terephthalate) (PBAT) is a promising biodegradable material. However, PBAT is also susceptible to photochemical transformations. To better understand how photochemistry affects the biodegradability of PBAT, we irradiated blown, nonstabilized, transparent PBAT films and studied their enzymatic hydrolysis, which is considered the rate-limiting step in polyester biodegradation. In parallel, we characterized the irradiated PBAT films by dynamic mechanical thermal analysis. The rate of enzymatic PBAT hydrolysis decreased when the density of light-induced cross-links within PBAT exceeded a certain threshold. Mass-spectrometric analysis of the enzymatic hydrolysis products of irradiated PBAT films provided evidence for radical-based cross-linking of two terephthalate units that resulted in the formation of benzophenone-like molecules. In a proof-of-principle experiment, we demonstrated that the addition of photostabilizers to PBAT films mitigated the negative effect of UV irradiation on the enzymatic hydrolyzability of PBAT. This work advances the understanding of light-induced changes on the enzyme-mediated hydrolysis of aliphatic-aromatic polyesters and will therefore have important implications for the development of biodegradable plastics.

Mechanical and Electrical Properties of Polylactic Acid with Aliphatic-Aromatic Polyester

Assuming an application where polylactic acid (PLA), a hard bioplastic, is used to sheath electrical wire, the author added 20 wt% of aliphatic-aromatic polyester or polybutyrate adipate terephthalate (PBAT), a soft resin, to PLA and then investigated the softened PLA’s mechanical and electrical properties. As a result of adding PBAT to PLA, Tg shifted to about 10°C lower than PLA. In addition, adding PBAT to PLA made the PLA softer and even more so at temperatures above 40°C. Furthermore, adding PBAT to PLA decreased the electric breakdown strength (EB) of the PLA by about 1 MV/cm over the temperature range of 0°C to 50°C, and EB was slightly higher than that of PVC over the temperature range of −10 to 60°C.

Effect of surface property of halloysite on the crystallization behavior of PBAT

Abstract Halloysite (Hal), calcined Hal, and organosilane-modified Hal were used as filler for the preparation of Hal/PBAT nanocomposite. XRD, SEM, XPS, FTIR, DSC, POM, and Avrami, Jeziorny, Kissinger models were used to characterize the surface property of Hal and its effect on the crystallization morphology, structure and kinetics of nanocomposites. Hydrogen bonding, generated between NH2 or –OH groups on surface of organosilane-modified calcined Hal or calcined Hal and C (C O) O in ester of PBAT, efficiently enhanced the nucleation ability of Hal nanofiller, resulting in increment of crystallization temperature, decrease of half time, but retard the transport of PBAT molecules chains. The stronger the hydrogen bond was, the more remarkable such influence was. This study provides a promising approach of tailoring the surface characteristic of Hal to manipulate the crystallization of biodegradable aliphatic-aromatic polyesters, especially with extreme low loading of Hal nanofiller.

Thermal, structural and degradation properties of an aromatic–aliphatic polyester built through ring-opening polymerisation

The novel biodegradable aromatic–aliphatic polyester, poly(2-(2-hydroxyethoxy)benzoate), was explored through thermal analysis, X-ray diffraction, dynamic mechanical analysis and comparative bio and catalysed degradation.