Alain Copinet

Biodegradation study of a starch and poly(lactic acid) co-extruded material in liquid, composting and inert mineral media

Abstract The biodegradation of a co-extruded starch/poly(lactic acid) polymeric film was studied in liquid, inert solid and composting media. Main mechanical properties of this film were Youngs modulus: 2340 MPa , elongation at break: 50%, contact angle: 118°. Mineralization of the materials carbon content was followed using the appropriate experimental methods of the International Standard Organisation. Whatever be the biodegradation medium used, the percentage of mineralization was better than the required 60% value for the definition of a biodegradable material. Moreover, repartitioning of the materials carbon between the various degradation products produced was quantified throughout the duration of experimental runs. The presence of starch was found to facilitate biodegradation of the polylactic component, especially in liquid media.

Production of thermostable amylolytic enzymes by Thermococcus hydrothermalis

A cell extract of Thermococcus hydrothermalis, grown for 6 h, gave α-glucosidase activity at 14.9 U/l, degrading oligosaccharides and maltose. α-Amylase, α-glucosidase and pullulanase activities were detected at 289 U/l, 13.5 U/l and 30 U/l respectively in the culture medium after 24 h growth of the archaeum. All of three enzymes, characterised by a half-life time of 1 to 5 h at 95°C, degraded both the α(1→4) and α(1→6) linkages of polysaccharides and the α(1→4) linkages of oligosaccharides.

Photodegradation and Biodegradation Study of a Starch and Poly(Lactic Acid) Coextruded Material

To simulate the behavior of agricultural mulch coextruded poly(lactic acid)(PLA)/starch films, two stages were carried out. The first was an ultraviolet treatment (UV) at 315 nm, during which glass transition temperature Tg, weight, and molecular weight (MW) decreased and a separation between PLA and starch phase was observed. For the second stage, the mineralization of the carbon of the material was followed using the ASTM (D 5209–92 and 5338–92) and ISO/CEN (14852 and 14855) standard procedures. To measure the biodegradability of polymer material, the assessment of the carbon balance allowed determination of the distribution between the carbon rate used to the biomass synthesis or the respiration process (released CO2), as well as the dissolved organic carbon into the culture medium and the carbon in the residual insoluble material. The influence of the nature of the medium and the standardized procedures on the final rate of biodegradation was investigated. Whatever the standardized method, the biodegradation percentage was significantly stronger in liquid medium (92.4–93.4) than on inert medium (80–83%). In the case of the compost process, only released CO2 was measured and corresponded to 79.1–80.3%.

Enzymatic degradation and deacetylation of native and acetylated starch-based extruded blends

Blends including natural starch and acetylated starch (with a substitution degree of 1.5) have been extruded to obtain an innovative packaging material. The influence of extrusion on the biodegradability of the blends was studied for several acetylated-to-raw starch ratios, by colourimetry (measure of reducing sugars) and chromatographic analysis (determination of the amounts of degradation products). The action of a single α-amylase (Termamyl LS 120 from Bacillus licheniformis) solely led to the degradation of unmodified parts of the starch. In order to increase the biodegradation rate of starch, the hydrolysis of acetylated groups was performed thanks to various acetyleterases, one coming from Sigma and the other one originating from the viscozyme. These acetylesterases will be refered to as Sigma acetylesterase (Sac) and Viscozyme acetylesterase (Vac), respectively. For identical percentages of ethanoic acid released, it appears that the biodegradation obtained after action of the α-amylase is more pronounced when the Sigma acetylesterase was utilized in a first step, because the biodegradation rate increased from 10 to 15%. The main degradation products are dp2 and dp5. Thus, the present work presents the degradation behaviour of a new packaging material, even at high acetylation value, provided the acetylesterase employed leads to a deacetylation compatible with the α-amylase.

Comparative Biodegradation Study of Starch- and Polylactic Acid-Based Materials

The degradation of starch- and polylactic acid-based plastic films by microorganisms extracted from compost was studied in a liquid medium. The various degradation products produced were measured throughout the duration of the experiment, and total carbon balances were estimated. For an easily biodegradable material, the evolution of the way carbon repartitioned between different degradation products was quite similar whatever the experimental condition or the type of substrate. On the other hand, for a resistant material exposed to these microorganisms, the nature of the biodegradation depended strongly on the experimental conditions. In the latter case, a differential scanning calorimetry analysis confirmed the importance of the applied norm on the state of the residual material. The consequences for improved methods of estimation of biodegradability of these materials are discussed.

An inert solid medium for simulation of material biodegradation in compost and achievement of carbon balance

The aim of this work was to create a vermiculite-based inert solid medium which could simulate compost medium and enable us to achieve complete carbon balances. As a first attempt, we decided to use starch to test several vermiculite media. We have compared the results obtained for these media with those obtained for starch degradation in compost, according to the shape of the mineralisation curves. The results obtained for compost and one activated vermiculite medium are very similar. This activated vermiculite medium was considered to be suitable to simulate starch degradation in compost. In this case, we have achieved complete carbon balances at different points in the test by taking samples in the medium. Different extraction steps have been performed on these samples to separate soluble carbon from biomass, and also from starch carbon remaining in the medium. After quantifying these different parts, we could establish complete carbon balances with a suitable accuracy.

A single step high temperature hydrolysis of wheat starch

Hydrolysis of native starch at 90°C by the α-amylase from Bacillus licheniformis and the α-glucosidase of Thermococcus hydrothermalis, an archaeum, has been investigated. The archaeal enzyme is optimally active at 110°C and pH 5.5. At 96°C, the half-life of the enzyme is 27 h in the presence of 10% (w/v) of starch. This α-glucosidase converts maltose into glucose and short oligosaccharides (G3 to G7) into glucose and maltose as the final products. Starch and long chain oligosaccharides are not hydrolysed by the enzyme. When the two enzymes were introduced simultaneously at the beginning of the hydrolysis a sugar syrup containing 74% (w/w) maltose and glucose was obtained after 24 h incubation. With 1 KNU α-amylase/g of starch and 3 U α-glucosidase/g of starch, the maximum rate of glucose production was 80 g × h−1 × 1−1.

Compostability of Co-Extruded Starch/Poly(Lactic Acid) Polymeric Material Degradation in an Activated Inert Solid Medium

The aim of this work was to estimate the biodegradation of a co-extruded starch/poly(lactic acid) polymeric material using a vermiculite based inert solid medium which could simulate compost medium and enable us to achieve complete carbon balances. At the end of the test the mineralisation rate was compared to those obtained for co-extruded starch/poly(lactic acid) polymeric material degradation in compost. It was shown that the mineralisation rate after 45 days of degradation was similar in activated vermiculite medium to the one in compost. A protocol for both extraction and quantification of the carbon included in the different degradation by-products was proposed and the carbon balance of the polymer degradation was followed during the test with a satisfactory accuracy. As the non-degraded PLA and starch material had been retrieved during the test, the evolution of the glass transition temperature and the molecular weight of PLA could be followed. A two-step degradation mechanism was highlighted in inert solid medium, showing the fundamental role of abiotic reactions for PLA degradation in compost.

Comparison of mineralization of starch in liquid, inert solid and compost media according to ASTM and CEN norms for the composting of packaging materials

Mineralization percentages of ground starch-based films are similar (68–72%), whatever the degradation medium and the norm used, with standard deviations less than 8%. Vermiculite, an inert solid medium, shows an intermediary behaviour, between liquid and compost media. Consequently, this support is suitable for further degradation studies, including the determination of carbon balances.

Aerobic Biodegradation of Extruded Polymer Blends with Native Starch as Major Component

The aerobic biodegradation of extruded blends containing native starch and an acetylated compound (starch or cellulose) was studied with the Bacillus amyloliquefaciens strain and also with the Biolen mixture known for its amylolytic activity. In the presented experiments, the rate of biodegradation is related to the percentage of acetylated compound in the blend. In fact, if the blend hydrolysis is facilitated by the amorphous state of the substrate, the inhibitory action of the acetyl group content is the major factor responsible of the weak hydrolysis. For instance, the conversion of the carbon material into CO 2 decreases strongly from 39% (native starch alone) to 7% (equimolar blend of starch and acetylated compound). All the other parameters used to estimate the hydrolysis extent (as the production of reducing sugars or acetic acid release) lead to the same conclusion.