Abstract
In the present work, a functionalization of polylactic acid (PLA) has been carried out to anchor maleic anhydride onto the main polymer chain to promote improvement in the compatibility of this polymer matrix with cellulose fibres. Low-molecular-weight PLA has been reacted with maleic anhydride following different procedures: a bulk reaction in an internal mixer and a solution reaction. The presence of oxygen during bulk processing did not allow for functionalization, guiding the reaction towards a decrease in the molecular weight of the material. On the contrary, a controlled reaction under an inert atmosphere in the presence of dioxane as the solvent, at reflux temperature, led to the functionalization of the polymer reaching different yields depending on the percentage of radical initiator and maleic anhydride added and reaction time. The yield of functionalization has been monitored by acid number titration as well as 1H NMR, with optimal yield values of functionalization being up to 3.5%. The PLA-functionalized formula has been used to make commercial PLA compatible with cellulose fibres derived from a thermomechanical treatment. The addition of 10% w/w of fibres to PLA increases the ultimate tensile strength (UTS) of PLA by up to 15%. The incorporation of 4 w/w of the already-functionalized coupling agent to the composite produces improvements in UTS of up to 24% regarding PLA, which confirms the functionalization from a performance point of view.
Highlights
Academic Editor: Aleksander MucCellulose-reinforced polymer composite materials have been promoted as an alternative to common plastic or synthetic fibre-reinforced composites [1,2]
The synthesis of the coupling agent must be performed in a solvent system and under an inert atmosphere (N2 )
The use of a 4% of coupling agent in PLAc + 10% BKF composites produced an increment in the tensile strength of around 24% in comparison with the composite without coupling agent that produced an increment of 15%
Summary
Cellulose-reinforced polymer composite materials have been promoted as an alternative to common plastic or synthetic fibre-reinforced composites [1,2]. The coupling agent bonded to the cellulose fibres diffuses in the polymer matrix, enhancing the dispersion of the fibres [8] This is the case in the successful example of maleic-anhydride-grafted polypropylene (MAPP) or polyethylene (MAPE) used in polypropylene and polyethylene. Materials 2022, 15, 1161 same time, the coupling agent bonded to the cellulose fibres diffuses in the polymer ma of 17 trix, enhancing the dispersion of the fibres [8] This is the case in the successful example of maleic-anhydride-grafted polypropylene (MAPP) or polyethylene (MAPE) used in polypropylene and polyethylene composites (PP and PE). These coupling agents need to be(PP prepared from the same polymer matrix as usedneed in the material to composites and PE). Once the solvent system showed efficiency in the grafting, parameters were modified to obtain the higher grafting degree and tested in a 10% reinforced composite material
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