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. 2022 Sep 1;14(17):3608.
doi: 10.3390/polym14173608.

Evaluation of Natural and Modified Castor Oil Incorporation on the Melt Processing and Physico-Chemical Properties of Polylactic Acid

Raluca Nicoleta Darie-Niță  1 , Anamaria Irimia  1 , Vasile Cristian Grigoraș  1 , Fănică Mustață  1 , Niță Tudorachi  2 , Maria Râpă  3 , Joanna Ludwiczak  4 , Andrzej Iwanczuk  4
Affiliations

Evaluation of Natural and Modified Castor Oil Incorporation on the Melt Processing and Physico-Chemical Properties of Polylactic Acid

Raluca Nicoleta Darie-Niță et al. Polymers (Basel). .

Abstract

Bio-based plasticizers derived from renewable resources represent a sustainable replacement for petrochemical-based plasticizers. Vegetable oils are widely available, non-toxic and biodegradable, resistant to evaporation, mostly colorless and stable to light and heat, and are a suitable alternative for phthalate plasticizers. Plasticized poly(lactic acid) (PLA) materials containing 5 wt%, 10 wt%, 15 wt% and 20 wt% natural castor oil (R) were prepared by melt blending to improve the ductility of PLA. Three castor oil adducts with maleic anhydride (MA), methyl nadic anhydride (methyl-5-norbornene-2,3-dicarboxylic anhydride) (NA) and hexahydro-4-methylphthalic anhydride (HA), previously synthesized, were incorporated in a concentration of 15 wt% each in PLA and compared with PLA plasticized with natural R. The physico-chemical properties of PLA/R blends were investigated by means of processability, chemical structure, surface wettability, mechanical, rheological and thermal characteristics. The addition of natural and modified R significantly improved the melt processing by decreasing the melt viscosity by ~95%, increased the surface hydrophobicity, enhanced the flexibility by ~14 times in the case of PLA/20R blend and ~11 times in the case of PLA/15R-MA blend as compared with neat PLA. The TG/DTG results showed that the natural R used up to 20 wt% could significantly improve the thermal stability of PLA, similar to the maleic anhydride-modified R. Based on the obtained results, up to 20 wt% natural R and 15 wt% MA-, HA- or NA-modified R might be used as environmentally friendly plasticizers that can improve the overall properties of PLA, depending on the intended food packaging applications.

Keywords: castor oil; mechanical properties; plasticizer; poly(lactic acid); rheology; thermal properties.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Structure of the major component of castor oil: triester of glycerol and ricinoleic acid [14].
Scheme 2
Scheme 2
The chemical structures of (a) R-MA, (b) R-NA, and (c) R-HA.
Figure 1
Figure 1
Normalized ATR-FTIR spectra of PLA/R samples compared with neat PLA and R: (a) 2750–3050 cm−1 and (b) 600–1900 cm−1 spectral range.
Figure 2
Figure 2
Normalized ATR-FTIR spectra of PLA/modified R samples compared with neat PLA and PLA/15R samples: (a) 2750–3050 cm−1 and (b) 600–1900 cm−1 spectral range.
Figure 3
Figure 3
Icrystalline/Iamorpous ratio derived from FTIR data.
Figure 4
Figure 4
Water contact angle of (a) neat PLA and PLA-based materials containing pure castor oil; (b) PLA-based materials containing anhydrides modified castor oil.
Figure 5
Figure 5
Mechanical properties for neat and plasticized PLA: (a) elongation at break, (b) tensile strength at break, (c) Young modulus.
Figure 6
Figure 6
Variation of (a) dynamic moduli (storage moduli and loss moduli) and (b) complex viscosity function of angular frequency for neat PLA and blends plasticized with natural castor oil.
Figure 6
Figure 6
Variation of (a) dynamic moduli (storage moduli and loss moduli) and (b) complex viscosity function of angular frequency for neat PLA and blends plasticized with natural castor oil.
Figure 7
Figure 7
Variation of (a) dynamic moduli (storage moduli and loss moduli) and (b) complex viscosity function of angular frequency for neat PLA and blends plasticized with modified castor oil.
Figure 8
Figure 8
DSC curves (exo up) from the second heating for neat PLA and PLA plasticized with natural and modified castor oil.
Figure 9
Figure 9
TG (a) and DTG (b) thermograms of castor oil (R), neat PLA and PLA/R blends.
Figure 10
Figure 10
TG (a) and DTG (b) thermograms of neat PLA and PLA containing 15 wt% modified castor oil.
See this image and copyright information in PMC

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