Biomacromolecules 2008, 9, 1007–1013
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Biodegradable Thermoplastic Composites Based on Polyvinyl Alcohol and Algae Emo Chiellini,* Patrizia Cinelli, Vassilka I. Ilieva, and Martina Martera Laboratorio Materiali Polimerici Bioattivi per Applicazioni Biomediche ed Ambientali, UdR-Consorzio INSTM, Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126 Pisa, Italy Received September 18, 2007; Revised Manuscript Received December 17, 2007
Algae constitute a largely available, low value material from renewable resources of marine origin to be used for the production of eco-compatible composites. Fibers of the green alga UlVa armoricana from the French coast were positively evaluated for the production of composites with a hydrophilic, eco-compatible polymer, such as poly(vinyl alcohol) (PVA) as continuous matrix by casting of aqueous suspensions and compression molding. PVA, Ulva, and starch were also successfully processed by the melt in the presence of glycerol. Positive results were obtained for film-forming properties and mechanical characteristics also with limited amounts of PVA (40%) attesting for Ulva suitability to be introduced in composites (up to 30%). Degradation in soil of Ulva and an Ulva-based composites outlined a rapid mineralization of Ulva in the selected medium (over 80% in 100 days) while the composite samples underwent a mineralization rate affected by the different component propensity to degradation.
Introduction The European Community is nowadays facing two environmental problems: algal proliferation on marine coastal regions from one side and the elimination of the plastic waste from the other side. The present paper reports part of the results obtained in the European Project BIOPAL.1 Sudden growth and uncontrolled proliferation of algae and seaweeds have occurred in several costal regions due to many environmental factors such as climate change and particularly eutrophication of seawater induced by agriculture and farming practices. Collection and storing of the algal material represent a problem for many communities. Data collected in BIOPAL outlined that in France, Brittany, in 2004 13000 tons of dry weight algae were collected, total Ulva was 7200 tons, and World Wide estimation was of 50000 tons dry/weight of Ulva. Thus a main priority is represented by the need to find practical and valuable application for the collected algae. Centers for the study and valorization of algae are present in Europe (France, Germany) responsible for collecting and treating algae in the form of thin powders or pellets available for industrial exploitation. Algae and seaweeds have been used for many years in agriculture, as manure, soil conditioners, and growing medium.2 The effectiveness of seaweed green manure has been demonstrated, mainly due to its high concentration of potassium salts but also to its trace elements and growth factors such as cytokinins, betaines, and auxins. Detached seaweeds or “total drift” have been used for many years in several European countries for the making of “lazy beds”. Soil or sand is layered with seaweed for vegetable production, particularly potatoes. However, seaweed decomposes very slowly and it is probably uneconomical to transport such material more than few kilometers inland.2 Very limited prior art has been found on the use of algae for the production of biobased composite materials. US56564103A * Corresponding author. Tel: +39-050-2210301. Fax: +39-050-2210332. E-mail:
[email protected].
and WO00/1106 patents deal with the use of algae for the production of films and foamed articles for packaging applications, respectively. PCT Int. Appl. WO 2007079719 deals with the use of algae in composites, and Italian Patent no. RM2002A000592 deals with the use of Ulva in tire production.3–7 Some studys of algae structure consider applications as filler in composite materials; the use of seaweeds in packaging flakes has also been proposed.7–11 Composites were prepared by mixing thermoplastic biodegradable polymers (Polycaprolactone, MaterBi) with sea algae fibers, but no further investigation has been reported.12 Poly(vinyl alcohol) (PVA), a hydrolysis product of poly(vinyl acetate), is well-suited for blends with natural polymeric materials since it is highly polar, can be manipulated in water solutions, and is also biodegradable by liquid media acclimated microorganism consortia. Composites based on PVA and natural polymeric and fibrous components, especially starch, have been prepared by casting of water solutions, calendering, and extrusion and subsequently proposed for use as single use items.13–20 Applications in agriculture (mulch films), civil constructions, one-time-use containers, and utilities (watersoluble laundry bags) are documented on Web sites of the following companies: MonoSOl AF21 and Idroplax.22,23 The major objective of the BIOPAL project was to contribute to solving the problem of plastic waste, to fight against the green algae plague by trying to generate profit through exploitation of this biomass as raw material for production of a new generation of functional bioplastics and biocomposites for agricultural, automotive, packaging, and industrial and environmental applications, and to develop and evaluate methods for assessment of biodegradability and biorecyclability of algaederived bioplastics and biocomposites including the development of standard test systems. Bioplastics were produced by blending the alga UlVa armoricana with poly(vinyl alcohol) (PVA). Ulva, Commonly called “sea-lettuce”, is a marine alga found in the littoral zone. It is found attached to solid rocks, wood supports such as logs,
10.1021/bm701041e CCC: $40.75 2008 American Chemical Society Published on Web 02/08/2008
1008 Biomacromolecules, Vol. 9, No. 3, 2008
Chiellini et al.
Table 1. Composition of Ulva (wt %) sand and other impurities ash pigment (methanol extraction) pigment (acetone extraction) F1a F2b F3c glucose xylose arabinose galactose chlorophyll a chlorophyll b AIRd a Fucoidans. b Crude alginate. residue (Klason procedure).
c
19.4 21.3 1.73 2.9 6.0 10.2 45.4 8.5 1.3 4.5 0.2 267 mg/g 288 mg/g 15
Insoluble residue.
d
Figure 1. SEM micrographs of Ulva powder: (a) raw fibers; (b) after removal of soluble fraction.
Acid insoluble
Table 2. Fiber Size Distribution in Micronized Ulva (U) sieve mesh
size (µm)
Ulva fibers (%)
40 40–50 50–70 70–100 100–140 140–270 270
φ > 425 300 < φ < 425 212 < φ < 300 150 < φ < 212 100 < φ < 150 53 < φ
