Chiellini and co-workers used algae as fillers and prepared poly(vinyl) alcohol (PVA) composites, via film casting, with green algae Ulva armoricana powder [1] and steam exploded Zostera marina [5]. The biodegradability in both cases has been improved. The addition of Ulva powder up to 30 wt% with particle dimensions below 150 μm led to the improved mechanical properties of PVA; above this concentration the cohesion of composites was poor. The mechanical properties of hybrid composites using Zostera steam exploded algae were improved only in the presence of additives such as starch and glycerol [5]. PLA/Zostera composites were very brittle, hence the highest content of algae was 20 wt% [5]. Significantly improved modulus and oxygen barrier properties of PVA were reported upon the addition of 10 μm size of Zostera flakes [14]. The Young’s modulus of various grades of Mater-Bi®, poly(ɛ-caprolactone) and polyhydroxybutyrate was improved with the addition of Ulva armoricana particles of 50–100 μm [7] and algae from Sardinia beaches (not specified) [6]. Green algae (Cladophora) fibres, having average length of around 600 μm, have also been successfully used in the preparation of isocyanate based foams [8]. The notion of algae as filler for thermoplastics has been also exhibited through international patents [9] and [10].
The goal of this work was to perform a comprehensive comparative study of the morphology and properties of composites blended with three types of algae, red, brown and green. PLA was chosen to keep 100% biobased nature of composites. The basic building block of PLA is lactic acid which is usually produced by carbohydrate fermentation. Often corn or potato starch is used as a source of carbohydrates thus rendering PLA fully bio-based polymer. No algae treatment was performed except sieving and selecting two populations of particles sizes, below 50 μm and from 200 to 400 μm. All composites were prepared in the same way, via melt mixing, allowing an adequate comparison between algae types. First, we characterised the initial algae: we analysed particle size distribution, their surface morphology and chemical composition together with bulk algae composition and crystallinity. Then we performed tensile testing of composites and compared the evolution of mechanical properties as a function of algae type, concentration and particles size.