Article

Hydrolytic degradation of biodegradable polyesters under simulated environmental conditions

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Abstract

In this study, the durability of poly(butylene succinate) (PBS), poly(butylene adipate-co-terephthalate) (PBAT), and PBS/ PBAT blend was assessed by exposure to 50 C and 90% relative humidity for a duration of up to 30 days. Due to the easy hydrolysis of esters, the mechanical properties of PBS and PBAT were significantly affected with increasing conditioning time. The PBS, PBAT, and PBS/PBAT showed an increase in modulus as well as a decrease in tensile strength and elongation at break with increased exposure time. Furthermore, the impact strength of PBAT remains unaffected up to 30 days of exposure. However, it was clearly observed that the fracture mode of PBS/PBAT changed from ductile to brittle after being exposed to high heat and humid conditions. This may be attributed to the hydrolysis products of PBS accelerating the degradation of PBAT in the PBS/PBAT blend. The differential scanning calorimetry results suggested that the crystallinity of the samples increased after being exposed to elevated temperature and humidity. This phenomenon was attributed to the induced crystallization from low molecular weight polymer chains that occurred during hydrolysis. Therefore, low molecular weight polymer chains are often favored to the crystallinity enhancement. The increase in crystallinity eventually increased the modulus of the conditioned samples. The enhanced crystallinity was further confirmed by polarizing optical microscopy analysis. Moreover, the hydrolysis of the polyesters was evaluated by scanning electron microscopy, rheology, and Fourier transform infrared spectroscopy analysis.

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... Lindstrom [16] monitored a process of hydrolysis of linear PBS in water and phosphate buffer at 37 C and 70 C and demonstrated significant dependence of weight loss of the PBS sample on temperature and pH. The hydrolysis of PBS has been covered by a number of other papers [17], and their results show that the temperature of hydrolysis leads to degradation of the material which significantly affects molecular weight and mechanical properties and changes the morphology [18] [19]. ...
... With regard to the greater degree of hydrolysis demonstrated by PBS at higher temperatures [17] and, thereby, potential increase in the degree of biodegradation under an anaerobic environment, the authors of this work focused on studying the behavior of PBS in thermophilic anaerobic sludge at 55 C. Simultaneously, changes in temperature T m and crystallization temperature T c were studied, and the kinetics of non-isothermal crystallization were evaluated using DSC alongside changes in the structure of PBS after the substance had undergone biodegradation. ...
... Is known that the ester linkages of PBS are more sensitive to elevated temperature and moisture [17] [18]. ...
Article
This work investigates the biodegradation of poly(butylene succinate) (PBS) in an environment of thermophilic (55°C) and mesophilic (37°C) anaerobic sludge. The thermophilic anaerobic sludge was prepared in a laboratory from mesophilic sludge sourced from a municipal waste water treatment plant and placed under thermophilic conditions. It was confirmed that PBS failed to decompose under mesophilic anaerobic conditions (2 wt. %), while the degree of biodegradation achieved under thermophilic conditions reached 24.8 wt. %. Abiotic hydrolysis of PBS in an environment of phosphate buffer (pH = 7) at 55°C reached 17.8%, leading to the conclusion that hydrolytic enzymes present in thermophilic anaerobic sludge are involved in the biodegradation process as well as abiotic hydrolysis. Nonisothermal crystallization kinetics of PBS before and after biodegradation was investigated by differential scanning calorimetry (DSC). After biodegradation, a large shift in melting temperature Tm was observed, while shift of crystallization temperature Tc was even more pronounced. Lower Tm means smaller crystals. Crystallization kinetics was approximately 50% slower, which could be explained by lower nucleation density. Scanning electron microscopy (SEM) revealed a beautiful spherulitic structure after biodegradation at elevated temperature. During biodegradation, microorganisms assimilated mostly in the amorphous part of the polymer, and elevated temperature helped healing of crystal imperfections. By X-ray diffraction (XRD), it was found that biodegradation does not have a large effect on crystal form of PBS.
... 16 The tensile properties of PBAT are comparable to low density polyethylene. 17 However, the high cost of PBAT limits its extensive applications in replacing non-biodegradable plastics. The optimal blending of PBAT with less expensive natural macromolecules such as soymeal could provide an inexpensive product with a favorable performance. ...
... All samples exhibited necking before failure. The overall tensile strength, modulus and elongation at break of all the PBAT-soy blend was comparable to other results [17] reported in the literature, As shown in Figure 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 21 revealed that the differences in tensile elongations were significant (p value <0.05) between neat PBAT and the blend films. Elasticity of polymers is an intrinsic property, and proteins (and pectins) in general have much lower plasticity than PBAT. ...
Article
The main goal of this research was to utilize an inexpensive soymeal (SM) rather than an expensive purified soy protein isolate and soy protein concentrate for biobased and biodegradable sustainable film development. Green processing approaches of soymeal, with the aim of destructurizing its carbohydrates that are deterrent to plastic making, were conducted. This process involves natural fermentation (NF), yeast fermentation (YF), and simultaneous enzyme saccharification and fermentation (YEF). Soymeals treated as such were then plasticized with glycerol and blended with poly(butylene adipate-co-terephthalate) (PBAT). Compatibilization of the fermentation treated and plasticized soymeal with PBAT was also conducted via reactive extrusion. The resulting blended materials were then extrusion casted to produce films of 0.35 mm thickness. The performance of the film, including mechanical, thermal, morphology, and water resistance as a function of the fermentation treatments, and compatibilization were evaluated. Composition analysis and a morphology study showed that YEF provided better destructurization of carbohydrates leaving behind a protein rich residue that was used for film making. Consistent with this observation, the YEFSM-PBAT blend films exhibited better tensile properties, thermal stability, and moisture resistance. Also, significant improvements in tensile strength, water resistance, and thermal stability of the films were achieved as a result of the compatibilization of PBAT with the plasticized protein meals. Fermentation of soymeal was found to be an effective and inexpensive method of destructurizing unnecessary carbohydrates for plastic production without the use of any toxic chemicals or extraction techniques. These results can be extended to other protein rich biomasses such as canola meal and corn meal. The developed blend films showed promising performance with several potential biodegradable applications including consumer bags, packaging film, agricultural mulch film, and silage wraps.
... The impact toughness/strength of the PBS is insufficient for a wide range of applications [2]. Blending PBS with PBAT can enhance the impact and tensile toughness of the PBS [3]. However, these polymers still cannot be used for wide range of applications on their own because they cannot fulfill some of the product requirements [4]. ...
... Melt flow index of PBS/PBAT (60/40 wt%) blend 33±3 g/10min (190 o C with 2.16 kg) Notched Izod impact strength of PBS/PBAT (60/40 wt%) blend Non-break [3] Onset thermal degradation of miscanthus fiber* ~260 o C Density of the miscanthus fibers 1.41 g/cm 3 [7] Modulus of the miscanthus fibers 9.49 GPa [8] *measured by thermogravimetric analysis (TGA) with a heating rate of 20 o C/min under nitrogen atmosphere.Table 3. A complete summary of all the experiments and the related mechanical properties of PBS/PBAT/miscanthus composites ...
Article
Full-text available
Injection molded biocomposites from a new biodegradable polymer blend based matrix system and miscanthus natural fibers were successfully fabricated and characterized. The blend matrix, a 40:60 wt% blend of poly(butylene adipate-co-terephthalate), PBAT and poly(butylene succinate), PBS was chosen based on their required engineering properties for the targeted biocomposite uses. A big scientific challenge of biocomposites is in improving impact strength within the desired tensile and flexural properties. The stiffness-toughness balance is one of the biggest scientific hurdles in natural fiber composites. Thus, the key aspect of the present study was in investigating an in-depth statistical approach on influence of melt processing parameters on the impact strength of the biocomposite. A full factorial experimental design was used to predict the statistically significant variables on the impact strength of the PBS/PBAT/miscanthus biocomposites. Among the selected processing parameters, fiber length has a most significant effect on the impact strength of the biocomposites.
... The band at 1325 cm -1 was created from the asymmetric vibration of the CH 2 group in the PBS backbone. The group at 1710-1713 cm -1 was formed from the bending of the PBS ester group (C=O) [20]. ...
... 16,17 It has also been blended within polylactic acid (PLA) 18 and used as reinforcement for polybutylene succinate (PBS) 19 and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). 20 Poly(butylene adipate-co-terephthalate) (PBAT) is a synthetic biodegradable thermoplastic copolyester, possessing comparable mechanical properties to PE. 21 Extensive research and development have been carried out with PBAT in recent decades due to its wide use in applications such as food packaging, agriculture, and biomedical fields. 22,23 Despite the numerous potential applications, its high production costs and poor stability under irradiation, which results in severe deterioration of its mechanical properties, still represent the main limitations, especially for the use of PBAT as a mulching film. ...
Article
Renewable and biodegradable UV-blocking films are in high demand for the increasing need of sustainable environment. Lignin can offer significant UV absorption, but it deteriorates the mechanical properties of films at a high content. In this effort, biobased 10-undecenoic and oleic acids were successfully grafted on soda lignin via solvent- and catalyst-free processes, as confirmed by ³¹P and ¹H NMR and Fourier transform infrared (FTIR). The resulting lignin ester derivatives and neat lignin were then melt-blended with a biodegradable poly(butylene adipate-co-terephthalate) (PBAT) to prepare UV-protective films. The incorporation of the modified lignins into the PBAT matrix exhibited good dispersion of lignin particles with almost unaffected tensile properties as well as good thermal stability for up to 20 wt % loading of lignin derivatives. The resulting films showed excellent UV-barrier property with 10 wt % lignin loading, having full protection in the whole UV-irradiation range (280-400 nm). The UV protection of prepared films proved persistent even after UV irradiation for 50 h, and their transparency was evidently enhanced. This work demonstrates a very promising procedure to produce high-performance and biodegradable PBAT-lignin UV-blocking films.
... The substitution of conventional synthetic polymers for the biodegradable in some production sectors is being implemented; however, factors that need a deeper research and development still exist, like the production cost and the assurance of the wanted properties through a long time. When biodegradable polymers are used, special care is mandatory to analyze the environment that they will be inserted, seeking to assure the materials useful life because the process of biodegradation can be initialized by factors like the presence of water (Muthuraj et al., 2014), luminous radiation (Parra et al., 2011), or the action of microorganisms (Iwanckuz et al., 2011). At this scenario, the properties control is fundamental so the material do not suffer failures during its use, mainly the control of polymers degradation, that can take a molar weight reduction and variation of crystallinity, affecting the material mechanical, thermal, and optical properties (La Mantia & Morreale, 2011;Nyambo et al., 2010). ...
Chapter
Recently, has occurred an increase in consumption of polymer materials products, especially synthetic from non-renewable sources. These materials often do not have sufficient properties to be used in some applications, in which the performance have become more important. The polymer composites arise as an alternative to this issue, synergistically combining the appropriate properties of the polymeric matrix and the reinforcement component. However, the large production of these materials has also brought the problem of improper disposal of their products and a high time to decompose in nature. As a counter-proposal to this scenario, it is important to consider the increased use of biodegradable polymers in production sector, since these have a shorter decomposition time and effect on the environment, considered “peaceful”. In this sense, the utilization of composites using biodegradable polymer matrices is already a reality and has been increasingly used in sectors and applications such as tissue engineering, packaging, membranes and others. In this chapter, we intend to present a review of the main biodegradable composites developed in the last five years trying to describe properties advances and transformation process relating the biodegradable polymer matrices and reinforcements used in each case.
Article
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We studied the hydrolysis kinetics of amorphous polylactide. It was found the hydrolysis rate had a slow-to-fast transition at a certain molecular weight (Mn). This transition was not correlated with the mass loss and water uptake of samples, nor the pH values of testing media. We speculated that this transition was due to the slow diffusion of polymer chain ends. The chain ends did not significantly promote the hydrolysis of samples until their concentrations (approximately 1/Mn) reached a critical value. The degradation tests were also conducted over a temperature range from 37 to 90 degrees C. A time-temperature equivalent relationship of degradation processes was established and a master curve spanning a time range equivalent to 3-5 years at 37 degrees C was constructed. This master curve can be used to predict polymer degradation processes based on accelerated tests. The functional time and disappearance time of degradable polymers were also discussed.
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Poly(butylene succinate) (PBS) is a promising polymer for the production of bio-based and biodegradable materials. This study focuses on the development of novel tunable morphological states based on ternary blends comprising PBS. The other biodegradable polymers are selected from a set of poly(lactic acid) (PLA), poly(butylene adipate-co-terephthalate) (PBAT), and polycaprolactone(PCL). Three completely different morphological states are observed here for the ternary blends and are reported for the first time including: partial wetting for PBS/PLA/PCL in which PLA droplets self-assemble at the interface of PBS and PCL; complete wetting tri-continuous morphology for PBS/PLA/PBAT; and a highly unusual state combining both partial and complete wetting cases for the PBS/PBAT/PCL blend. The dramatic variation of morphology for these blends is possible due to very low interfacial tensions between the polymer pairs. Within these morphological wetting states a significant variety of specific structures can be obtained through control of the relative compositions. For example, for the partially wet xPBS/yPLA/50%PCL blend, changing the volume fraction of PBS to PIA from (phi PBS/phi PLA = 10 to (phi pgs/phi pLA = 0.1 results in a transformation from PLA droplets at the PBS/PCL interface to PBS droplets at the PLA/PCL interface. From the thermodynamic standpoint, the observed partial and complete wetting cases are supported by Harkins theory. This work opens the door to a wide range of novel and stable PBS-based ternary blend structures comprising biodegradable polymers.
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Based on information available in the literature and new investigations, the ageing behaviour of polypropylene at room temperature and in annealing was studied. Two effects have to be discerned: changes in the amorphous and/or mesomorphic regions of the material at room temperature, which lead to an increase in density and modulus in connection with embrittlement on the one hand, and relaxation- and recrystallization-processes at higher temperatures, which positively influence heat deflection temperature and impact strength alongside with modulus and density on the other hand. Use of elevated temperatures to accelerate ageing for the determination of long-term properties is therefore not possible in the case of polypropylene.
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The subsequent melting behaviour of poly(butylene succinate) (PBSU) and poly(ethylene succinate) (PES) was investigated using DSC and temperature modulated DSC (TMDSC) after they finished nonisothermal crystallization from the melt. PBSU exhibited two melting endotherms in the DSC traces upon heating to the melt, which was ascribed to the melting and recrystallization mechanism. However, one melting endotherm with one shoulder and one crystallization exotherm just prior to the melting endotherm were found for PES. The crystallization exotherm was ascribed to the recrystallization of the melt of the crystallites with low thermal stability, and the shoulder was considered to be the melting endotherm of the crystallites with high thermal stability. The final melting endotherm was ascribed to the melting of the crystallites formed through the reorganization of the crystallites with high thermal stability during the DSC heating process. TMDSC experiments gave the direct evidences to support the proposed models to explain the melting behaviour of PBSU and PES crystallized nonisothermally from the melt.
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The influence of annealing temperature on the fracture properties of iPP films (one homopolymer and two propylene–ethylene block copolymers) is presented. The fracture behaviour is studied by means of the Essential Work of Fracture (EWF) procedure, and is complemented by the study of the effect of thermal treatment on tensile properties and microstructure, using differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). It is shown that the initial metastable phase of quenched iPP films, widely known as smectic, transforms gradually into the monoclinic form as the annealing temperature is increased, resulting in an important improvement of the tensile properties, whereas the fracture parameters have different evolutions depending on the ethylene content. The reasons for a decrease in the essential work term and an increase in the plastic term as the crystal perfection grows are discussed on the basis of the microstructural changes of the crystalline phase and the smectic–monoclinic strain-induced phase transformation.
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Water is absorbed by most polymers, but a change of properties is induced only in specific types of polymers. Water is considered to be present in the free volume and active only when attached to polymer chains by hydrogen bonds. The materials considered are PEI, PEEK, PES, PC, PA 12, and PA 6. The changes in damping spectra, moduli, and thermal expansion due to the moisture absorption have been investigated in the broad temperature range of 4.2–320 K. It is surprising that properties are changed by water in a different or opposite ways at low and high temperatures. Even at very low temperatures, absorbed water influences the mechanical performance in an unexpected way. The results at low temperatures might be a tool for a better understanding of the features of the hydrogen bonded water, which itself could be a sensor for analysing molecular mobilities. The interpretation of results is generally not yet clear and some cryogenic results are in contradiction to well established correlations for dry polymers. Ideas for solving these problems are given in the conclusions of this study.
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Time-dependent mechanical design properties of four commercial thermoplastic resin systems were investigated at temperatures of 23, 100, and 150°C. The test materials were glass-filled polyamides and polyphthalamides. Experiments were performed to characterize creep, creep-rupture and tensile behaviors after isothermal aging. Creep-rupture data were used to create master curves using a Sherby–Dorn analysis. Although each material possessed a different property advantage, a polyphthalamide with 33% glass reinforcement exhibited a good combination of creep resistance, strength and ductility. The reported results provide information that is critical for the design and development of structural thermoplastic components.
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The effects of load and temperature on in vitro degradation behaviors of poly(glycolide-co-L-lactide) 90/10 multifilament braids were investigated in phosphate buffer solution at pH 7.4. The property changes of the braids with time were monitored by tensile test, gel permeation chromatography analysis, and scanning electron microscopy. The interrelationships between material properties, time and experimental conditions were explored. The results showed that the polymer braids gradually lost their strength and molecular weight with the increasing in vitro time. While the load levels applied had no effect on the materials, raising temperatures significantly accelerated the degradation. It was found that for a given tensile breaking strength retention (BSR), the dependence of degradation time on temperature could be illustrated by an Arrhenius-type equation, from which the activation energy could be derived. Further analysis indicated that there are well-defined relationships between molecular weight, BSR and breaking strain retention, and these relationships can be illustrated mathematically. Finally, the surface morphology of the fiber showed visible change during the degradation process.
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