Abstract
Composite filaments consisting of poly(lactic acid) (PLA) and micro crystalline cellulose (MCC) were successfully used for additive manufacturing (AM) by fused filament fabrication (FFF). PLA and MCC bio-composites were obtained by direct mixing in a melt compounder; maleic anhydride (MAH) was also grafted onto PLA in reactive mixing stage to evaluate its effect on the final properties of the printed material. Filaments with various concentrations of MCC (up to a maximum content of 10 wt%) were produced with a single screw extruder and used to feed a commercial desktop FFF printer. Upon grafting of PLA with MAH, a more coherent interfacial morphology between PLA and MCC was detected by electron microscopy analysis. The thermal degradation of the PLA was unaffected by the presence of MCC and MAH. According to differential scanning calorimetry and dynamic mechanical analysis results, micro-cellulose acted as nucleating agent for PLA. In fact, the crystallization peak shifted towards lowers temperature and a synergistic effect when MCC was added to PLA grafted with MAH was observed possibly due to the increase of the chain mobility. Micro-cellulose led to an increase in the stiffness of the material in both filaments and 3D printed specimen; however, a different fracture behavior was observed due to the peculiar structure of printed samples.
Highlights
Fused filament fabrication (FFF) is one of the more attractive additive manufacturing (AM) techniques due to the continuous decrease of the related costs, high speed and simplicity of the process [1]
Comparing the spectra of neat poly(lactic acid) (PLA) and the ones of PLA grafted with maleic anhydride, it is possible to observe the presence of new absorption band, in particular at: 695 cm-1 corresponding to cis-vinyl C-H bending [22]; 820 cm−1 corresponding to the out of plane deformation for carboxyl groups from MAH [40]; 1635 cm-1 corresponding to the cyclic C-C stretching that might be a confirmation of the chemical interaction between PLA and MAH [26, 40]; 1790 cm-1 and 1850 cm-1 are assigned to the symmetric and asymmetric stretching of the carbonyl groups of the saturated cyclic anhydride ring of MAH respectively [22, 24, 26, 41]
Filaments based on poly (PLA) and micro crystalline cellulose (MCC) were prepared by a two-steps process and used to produce samples by fused filament fabrication
Summary
Fused filament fabrication (FFF) is one of the more attractive additive manufacturing (AM) techniques due to the continuous decrease of the related costs, high speed and simplicity of the process [1]. Numerous investigations of free-radical grafting of MAH different polyolefins such as: LDPE, HDPE, PP, EPR, EPDM are reported in literature [21] This reaction is generally achieved when the molten polymer is mixed with MAH and with a peroxide initiator, either in an extruder or in an internal mixer. The hydrophilic functionalization with maleic anhydride was studied to improve the compatibility between PLA and wheat straw by Nyambo et al [30] Both PLA and starch are brittle components and lack of chemical compatibility, this results in a brittle composite with low strength, which could be improved by introducing MAH as a compatibilizer as demonstrated by Zhang et al [31]. PLA has been used to prepare bio-based and biodegradable composites filled with cellulosic materials to reduce the overall costs and improve the mechanical properties [37, 38]
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