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Foaming of PLA Cellulose Composites : Effect of Fibres on the Solidification and Crystallisation Behaviour

Abstract : In many industrial fields, the development of porous and light polymer composite structures is of great interest because of their several advantages compared to a massive solid of the same chemical nature. Batch foaming of polymers is a discontinuous process carried out normally in an autoclave. The samples are saturated in a pressurised vessel, and their foaming is achieved by inducing an instability into the system, which can be sudden drop in pressure or by a raise in temperature. Polylactic acid (PLA) is a well-known and commercially available biopolymer that can be produced from different sources. Its different characteristics generated a great deal of interest in various industrial fields as in the foaming one. PLA’s crystallisation kinetics is reported to be slow and can be enhanced by using different solid additives (filler) as crystal-nucleating agents [1-2]. It is known that crystallisation kinetics of polymers can influence different polymer shaping processes such as injection, moulding, foaming, etc and, that additives can modify the crystallisation kinetics of the polymers; but it is not reported in literature whether the shape and dimension of the additives matter and, consequently there is not information about their effect on processes like foaming. This works aims to understand the effect of the filler content and aspect ratio (length/diameter) on PLA’s solidification and crystallisation kinetics. Cellulose fibres (Rettenmaier France) of different aspect ratios (1 and 6) were compounded with PLA by extrusion at 5, 20 and 30 %wt, then injected into discs. Solidification and crystallization kinetics of the materials were evaluated through polarized optical microscopy with hot-stage (POM), isothermal DSC and oscillatory shear rheology (at an angular frequency of 1 rad/s). In all tests, pure PLA and composite samples were heated up to melting and then cooled to the desired isothermal crystallization temperature, ranging from 80 to 120 °C. In general, crystallisation induction (time to observe the first crystals) and half crystallisation times were reduced with increasing fibre content but also when increasing their aspect ratio. Crystallisation rate constant, increased with both, content and aspect ratio. Studying the evolution of the viscosity of the samples with time at a certain temperature, in general it was shown that after a first plateau corresponding to the beginning of the isotherm, a rise in viscosity attributed to the solidification of the polymer occurred. A second rise in viscosity corresponding to the crystallisation of the sample was observed depending on crystallisation conditions. This work shows that fibre content and aspect ratio are two important parameters in the solidifcation and crystallisation behaviour of PLA-cellulose composites. This result emphasizes that we can choose between two different additives or even master the crystallisation kinetics of PLA not only by chemical interactions between additives and PLA, but by just changing the aspect ratio of filler. This opens interesting perspectives for the development of bio-based materials and allows us to go one step further in the understanding of composites shaping processes dependent on crystallisation like foaming. An interesting question lies now on the table: can we master the foaming of PLA composites by changing the aspect ratio of the fillers to obtain materials with suitable functional properties?
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https://hal.mines-ales.fr/hal-03706877
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Soumis le : mardi 28 juin 2022 - 09:55:00
Dernière modification le : vendredi 5 août 2022 - 11:43:51

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  • HAL Id : hal-03706877, version 1

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Jennifer Andrea Villamil Jiménez, Nicolas Le Moigne, Martial Sauceau, Romain Sescousse, Jean-Charles Benezet, et al.. Foaming of PLA Cellulose Composites : Effect of Fibres on the Solidification and Crystallisation Behaviour. EPF 2022 - European Polymer Congress, Jun 2022, Prague, Czech Republic. , 2022. ⟨hal-03706877⟩

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