Degradable or not? Cellulose acetate as a model for complicated interplay between structure, environment and degradation

High-Sensitivity Metal Oxide Sensors Duplex for On-the-Field Detection of Acetic Acid Arising from the Degradation of Cellulose Acetate-Based Cinematographic and Photographic Films

In this work, a system consisting of two resistive sensors working in tandem to detect and quantify the acetic acid released during the degradation of cellulose acetate-based ancient cinematographic and photographic films is presented. Acetic acid must be constantly monitored to prevent reaching concentrations at which autocatalytic degradation processes begin. The sensors are constituted by a thin layer of metal oxide (tungsten oxide and tin oxide) deposited over an interdigitated electrode capable of being heated, chosen to maximize the array response towards acetic acid vapors. The signals obtained from the sensor array are mathematically processed to reduce the background signal due to interferent gases produced during degradation of ancient cinematographic films. The sensor array reported a LOD of 30 ppb for acetic acid, with a linearity range up to 30 ppm. Finally, the sensor array was tested with different cinematographic and photographic film samples made of cellulose acetate, whose degradation state and acetic acid production was validated using the conventional technique (A-D strips). The presented array is suitable for remote monitoring large number of films in collections since, compared to the official technique, it has a lower detection limit (30 ppb vs. 500 ppb) and is much quicker in providing accurate acetic acid concentration in the film boxes (15 min vs. 24 h).

Strategies and progress in synthetic textile fiber biodegradability

Abstract

The serious issue of textile waste accumulation has raised attention on biodegradability as a possible route to support sustainable consumption of textile fibers. However, synthetic textile fibers that dominate the market, especially poly(ethylene terephthalate) (PET), resist biological degradation, creating environmental and waste management challenges. Because pure natural fibers, like cotton, both perform well for consumer textiles and generally meet certain standardized biodegradability criteria, inspiration from the mechanisms involved in natural biodegradability are leading to new discoveries and developments in biologically accelerated textile waste remediation for both natural and synthetic fibers. The objective of this review is to present a multidisciplinary perspective on the essential bio-chemo-physical requirements for textile materials to undergo biodegradation, taking into consideration the impact of environmental or waste management process conditions on biodegradability outcomes. Strategies and recent progress in enhancing synthetic textile fiber biodegradability are reviewed, with emphasis on performance and biodegradability behavior of poly(lactic acid) (PLA) as an alternative biobased, biodegradable apparel textile fiber, and on biological strategies for addressing PET waste, including industrial enzymatic hydrolysis to generate recyclable monomers. Notably, while pure PET fibers do not biodegrade within the timeline of any standardized conditions, recent developments with process intensification and engineered enzymes show that higher enzymatic recycling efficiency for PET polymer has been achieved compared to cellulosic materials. Furthermore, combined with alternative waste management practices, such as composting, anaerobic digestion and biocatalyzed industrial reprocessing, the development of synthetic/natural fiber blends and other strategies are creating opportunities for new biodegradable and recyclable textile fibers.

Article Highlights

Crystal structure of acetylxylan esterase from Caldanaerobacter subterraneus subsp. tengcongensis

The acetylxylan esterases (AXEs) classified into carbohydrate esterase family 4 (CE4) are metalloenzymes that catalyze the deacetylation of acetylated carbohydrates. AXE from Caldanaerobacter subterraneus subsp. tengcongensis (TTE0866), which belongs to CE4, is composed of three parts: a signal sequence (residues 1-22), an N-terminal region (NTR; residues 23-135) and a catalytic domain (residues 136-324). TTE0866 catalyzes the deacetylation of highly substituted cellulose acetate and is expected to be useful for industrial applications in the reuse of resources. In this study, the crystal structure of TTE0866 (residues 23-324) was successfully determined. The crystal diffracted to 1.9 Å resolution and belonged to space group I212121. The catalytic domain (residues 136-321) exhibited a (β/α)7-barrel topology. However, electron density was not observed for the NTR (residues 23-135). The crystal packing revealed the presence of an intermolecular space without observable electron density, indicating that the NTR occupies this space without a defined conformation or was truncated during the crystallization process. Although the active-site conformation of TTE0866 was found to be highly similar to those of other CE4 enzymes, the orientation of its Trp264 side chain near the active site was clearly distinct. The unique orientation of the Trp264 side chain formed a different-shaped cavity within TTE0866, which may contribute to its reactivity towards highly substituted cellulose acetate.

Preparation of bio-based cellulose acetate/chitosan composite film with oxygen and water resistant properties

Plastic pollution has inspired the preparation of environmentally friendly bio-based plastics that can replace petroleum-based plastics. Herein, a composite film with oxygen and water resistant properties was prepared by a fluidized bed method, employing bio-based cellulose acetate (CA) as raw material, glycerol as a plasticizer, and chitosan and silica as additives. The addition of 15% chitosan greatly reduced the oxygen transmission rate of the CA film by 83.5%, and increased the tensile stress and tensile strain of the composite membrane, reaching 26.5 MPa and 22.2%, respectively. The deposition of silica particles is able to compensate for the undesired increase in the hydrophilicity caused by the addition of chitosan, and tune the hydrophilic nature of the surface of the CA/CS films to the hydrophobic nature, which is desirable for water-resistant applications. The prepared composite film displays good oxygen and water resistant properties and can be used for food packaging and related applications.

Carbon Dot-Triggered Photocatalytic Degradation of Cellulose Acetate

Chemical modification of biopolymers, before use in thermoplastic applications, can reduce the susceptibility to open environment degradation. We demonstrate carbon dots (CDs) as green photocatalytic triggers that can render the common cellulose derivative, cellulose acetate (CA), degradable under open environment relevant conditions. CD-modified cellulose acetate (CA + CD) films were subjected to UV-A irradiation in air and simulated sea water, and the degradation process was mapped by multiple spectroscopic, chromatographic, and microscopy techniques. The addition of CDs effectively catalyzed the deacetylation reaction, the bottleneck preventing biodegradation of CA. The photocatalytically activated degradation process led to significant weight loss, release of small molecules, and regeneration of cellulose fibers. The weight loss of CA + CD after 30 days of UV-A irradiation in air or simulated sea water was 53 and 43%, respectively, while the corresponding values for plain CA films were 12 and 4%. At the same time the weight average molar mass of CA + CD decreased from 62,000 to 11,000 g/mol and 15,000 g/mol during UV-A irradiation in air and simulated sea water, respectively, and the degree of substitution (DS) decreased from 2.2 to 1.6 both in air and in water. The aging in water alone did not affect the weight average molar mass, but the DS was decreased to 1.9. Control experiments confirmed the generation of hydrogen peroxide when aqueous CD dispersion was subjected to UV-A irradiation, indicating a free radical mechanism. These results are promising for the development of products, such as mulching films, with photocatalytically triggered environmental degradation processes.