Preparation and biodegradation of clay composites of PLA
Introduction
Biodegradable synthetic polymers are promising candidate materials in biomedical applications. Polymeric materials can be produced in various shapes as medical devices such as pins, rods, screws and suture. Moreover, they can be functionalised to contain cells, growth factors, drugs and molecules to obtain a positive biological response.
In this context several polymers have been exstensively described, e.g. poly(glycolic acid), poly(l-lactic acid), poly(caprolactone), poly(propylene fumarate), polyanhydrides, polycarbonates, polyurethanes and polyphosphazenes.
In particular, polyesters have shown to be biocompatible: they are, in fact, used in a number of clinical applications, such as resorbable sutures, drug delivery systems and orthopedic fixation devices. They are also easily degraded by hydrolysis of ester bonds and degradation products are reabsorbed through the metabolic pathways [1], [2].
We have focused our attention on poly(lactic acid) (PLA), because it is made from renewable agriculture products and it is among the few biodegradable polymers approved by the Food and Drug Administration for medical use, because of its demonstrated biocompatibility [3], [4], [5], [6].
PLA is a linear aliphatic thermoplastic polyester, produced by polymerization of lactide, a cyclic dimer derived from lactic acid, which in turn is obtained by the fermentation of corn or sugar beet.
In order to improve PLA mechanical properties and to accelerate its degradation rate, different polymer/silicate nanocomposites are explored: montmorillonites and fluorohectorites clays or organoclays, are blended with the polymer. The safety of clays in food, cosmetics and medical application is widely supported in literature [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22].
Following these preliminary considerations, the properties of different PLA/clays composites and their behaviour in aqueous environment were studied.
According to Okamoto [23], the combination of polymer and clays, at the nanoscale, often results in remarkably improved mechanical and functional properties with respect to pure polymers or conventional composites (either micro- or macrocomposites). Higher modulus, increased strength and heat resistance, decreased gas permeability and flammability, increased degradation rate in the case of biodegradable polymers have been reported.
Changes observed can be ascribed to a more efficient interfacial interaction between matrices and organically modified layered silicates (OMLSs), with respect to conventional composites. Layered silicates (LSs) have layer thickness in the order of 1 nm and very high aspect ratios (e.g. 10–1000). A small weight percentage of OMLSs, properly dispersed throughout the matrix, thus leads to a much larger surface area to exploit interfacial interactions between the polymer and the filler than in conventional composites.
Preparation, characterization, mechanical properties and biodegradation in blood plasma are discussed here. All nanocomposites exhibited significant improvement in mechanical properties and degradation when compared to pure PLA.
Section snippets
Materials
PLA 4042D was supplied from NatureWorks and consists of 92% l-lactide and 8% d-lactide units, with polydispersity index of 2 and a density of 1.25 g/cm3 [24].
Sepiolite CD1 (without organic modifier) was purchased by Tolsa, Bentone SD2 (montmorillonite with an aryl modifier) by Elementis, Somasif MEE (fluorohectorite with a dihydroxy organic modifier) by Unicoop, Nanofil 804 (montmorillonite with a dihydroxy organic modifier) by Süd Chemie and Cloisite 30B (montmorillonite with a dihydroxy
General aspects
The degradation experiments carried out in plasma show a general enhancement of opacity of the samples, except for neat PLA. In accordance with Paul et al. (2005) [25], the opacity increases according to the incubation time and the colour turns to white. Nanocomposites samples tend to wrinkle instead of maintaining a planar geometry as in pure PLA.
Lactic acid release
Lactic acid release by polymer/clay nanocomposite samples is reported with respect to lactic acid release from pure PLA: every 25 days, the amount of
Conclusions
The goal of this work was to compare the mechanical properties and biodegradability of PLA nanocomposites in respect to neat polymer for perspective biomedical applications.
The nanoreinforcements chosen for this study were layered silicate. Results showed an influence of the type of nanoreinforcement on the interaction with the PLA Matrix. Consequently, also the mechanical properties and degradability were affected.
The nanocomposites showed a general improved mechanical behaviour depending on
Acknowledgements
The work is performed within the “Progetto Lagrange – Fondazione C.R.T.” under the supervision of Professor Giovanni Camino, Politecnico di Torino (Alessandria branch).
The authors are grateful also to Dr. Paola Rizzarelli, CNR Researcher Institute of Chemistry and Technology of Polymers (ICTP), Catania; to the members of Proplast-Consortium, Alessandria and of Politecnico di Torino for precious help.
A special thanks to Dr. Jenny Alongi, Politecnico di Torino (Alessandria branch) for fruitful
References (28)
- et al.
Polymer
(2001) - et al.
J. Hazard Mater.
(2007) - et al.
Water Res.
(2008) - et al.
Poult. Sci.
(2004) - et al.
Gastroenterology
(1983) - et al.
Poult. Sci.
(2005) - et al.
Appl. Clay Sci.
(2007) Appl. Clay Sci.
(2002)- et al.
Polymer
(2006) - et al.
Degée, F. Monteverde, Pol. Degr. Stab.
(2005)
Polymer
Biomaterials
Eur. Cell. Mater.
Mater. Res.
Cited by (119)
A review on the modification of polypropylene carbonate (PPC) using different types of blends/composites and its advanced uses
2023, Materials Today CommunicationsPreparation a skin disease UV protection polylactic acid film and crystallinity, mechanical properties characterization
2022, Materials Today CommunicationsBiodegradation of modified Poly(lactic acid) based biocomposite films under thermophilic composting conditions
2019, Polymer TestingCitation Excerpt :Authors have prepared and investigated PLA films as well as PLA composites because these offers wide scope of research for further improvement of PLA based packaging systems [25–29]. Series of literature investigated PLA based biocomposite packaging systems under different environments, like in soil, composting and industrial composting conditions [15,17,23,29–34]. Various studies used different analytical techniques that have been employed for evaluation of biodegradation during composting of biopolymers using either direct or an indirect approach.
CO2 evolution rate was the highest for PLA/chitosan sample at 1.13 day−1. Experimental data of all the test samples showed a good fit (R2 ~ 99.99) with the kinetic model. Morphological analysis by FESEM confirmed the erosion of polymer during composting.