Fast hydrolyzable polyesters are promising candidates as biodegradable plastics degrading to carbon dioxide, water, and biomass in the presence of oxygen in a suitable environment. The rate-determining step of biodegradation is the fragmentation of polyesters to lower mass fragments by hydrolysis, which in the second step undergo bioassimilation. Polyesters with a balance of good mechanical properties and fast hydrolyzability are urgently needed as a sustainable solution to the problem of plastic pollution and persistent microplastics when used in packaging and agricultural applications. Aromatic polyesters, such as poly(butylene terephthalate) (PBT), are mechanically strong but require harsh hydrolysis conditions, making them nonbiodegradable. The trend is mostly the opposite for aliphatic polyesters. We present in this work an aromatic polyester, a constitutional isomer of PBT [poly(1,4-benzenedimethylene succinate) (PBDMS)], and its copolymers (PB x BDM y S) in which aliphatic ester units balance the mechanical, thermal, and hydrolysis properties. PBDMS was prepared from 1,4-benzenedimethanol (BDM) and succinic acid (S) via two-step polycondensation. Its copolyesters with 1,4-butanediol (B) as a comonomer are also presented. High-molecular-weight PBDMS showed a glass-transition temperature of 6 °C and a melting temperature around 100 °C, very high thermal stability, and melt processability. The structure−property relationship of such polyesters was intensively studied, focusing on the impact of molecular composition. The stress−strain behavior of these (co-)polyesters largely depended on the content of BDM and covered a wide range from ductile to elastic to brittle materials. The films of these polyesters showed much faster hydrolysis under basic conditions, making them promising for future detailed degradation studies under different environmental conditions.
Natural biopolymers, which are environmentally friendly materials, are an appealing resource for producing edible films. Edible packaging films may be consumed with the food or beverage that they hold since they are made from edible components derived from plants and animals. Even if they are not consumed, they disintegrate quickly, significantly reducing the waste disposal problem. In this work, karaya dialdehyde (KDA) with a variable aldehyde content is effectively produced through the periodate oxidation of gum karaya and subsequently used as an eco‐friendly crosslinking agent for edible gelatin films. Chemical crosslinking between the gelatin protein chains is generated when KDA is added, producing a water‐stable film. The mechanical properties are found to be significantly improved as a result of the covalent bonding between the two polymers. Excessive oxidation, on the other hand, has a detrimental effect on the film properties. Despite the crosslinking, the films are biodegradable, suggesting that composite films made in an environmentally benign manner in an aqueous media using polymers derived from biosources may be utilizable in the edible film‐based packaging sector.
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 (PB x BDM y S) 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.
Lately, environmentally benign packaging materials with biodegradability, flexibility, and high barrier properties are sought after as a substitute for conventional plastic packaging materials due to increasing plastic pollution and microplastics in the environment. Although natural polymers can be sustainable alternatives to petro-sourced, non-biodegradable plastics, they suffer from the poor barrier and mechanical properties. In this study, a mechanically stable, biodegradable film of tree gum kondagogu with remarkable barrier properties is fabricated. The introduction of spray-coated, waterborne, large-aspect ratio sodium-hectorite dispersion on tree-gum films ensured very high barrier properties even at high relative humidity conditions (oxygen transmission rate (OTR) ≈1.7 cm 3 m −2 day −1 bar −1 at 75% relative humidity). The coating not only decreases gas permeability through the films but also minimizes the sensitivity of performance to humidity levels. The clay-coated nanocomposite films outperformed various commercial polymers and are comparable to high-performance packaging films in terms of oxygen barrier properties. Further, the coating improved the mechanical properties of the films rendering them a prospective packaging material. These biodegradable, high-barrier and mechanically robust films are a promising advance in the field of sustainable packaging.
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