|Hikmatun Ni'mah||Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo, Surabaya 60111, Indonesia|
|Rochmadi Rochmadi||Department of Chemical Engineering, Faculty of Engineering, Gadjah Mada University, Jl. Grafika No.2, Yogyakarta 55281, Indonesia|
|Eamor M. Woo||Department of Chemical Engineering, College of Engineering, National Cheng Kung University, Tainan 701, Taiwan|
|Dian Amalia Widiasih||Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo, Surabaya 60111, Indonesia|
|Siska Mayangsari||Department of Chemical Engineering, Faculty of Industrial Technology, Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo, Surabaya 60111, Indonesia|
In this study, poly(L-lactic acid) (PLLA) was blended with glycerol as a plasticizer by the solution blending technique to form blend films. The glycerol content was varied in order to evaluate the effect of glycerol content on the PLLA properties and to obtain an optimum weight ratio of PLLA/glycerol (PLLA/Gly) blend films with improved properties. The effect of the addition of compatibilizer on the properties of the composite films was also observed. The properties of the films obtained were characterized by using FTIR, XRD, DMA and SEM. The FTIR spectra showed an increase in the intensity of the characteristic peak of glycerol with increasing glycerol content, indicating that the blending ratio and technique were precise. Based on the XRD analysis, the degree of crystallinity generally increased with the addition of glycerol. DMA analysis showed that the addition of glycerol reduced the value of tensile strength and Young’s modulus of the PLLA/Gly films, but increased the elongation at break. The optimum weight ratio was reached by the sample of PLLA/Gly (80/20) with the value of tensile strength, Young’s modulus and elongation at break being 13.43 MPa, 747.8 MPa and 1.96%, respectively. The addition of compatibilizer slightly increased the flexibility of the composite films. DSC analysis showed an increase in flexibility after the addition of glycerol, indicated by a decrease in Tg, which supports the results of the DMA analysis. SEM analysis was made of the porous morphology on the fracture surface of the films after the addition of glycerol; the porous structure was more pronounced in the PLLA/Gly (80/20) film with compatibilizer, which could therefore be considered for application as a scaffold in tissue engineering after further analysis has been conducted.
Blend; Glycerol; Maleic anhydride; Plasticizer; Poly(L-lactic acid)
Poly(L-lactic acid) (PLLA) has
become an interesting material in some specific applications due to its
excellent properties, such as biocompatibility, biodegradability, high
mechanical properties and processability. However, PLLA still has some drawbacks, such
as brittleness due to its high crystallinity, hydrophobicity, and low thermal
stability, which lead to limitations in its utilization. One of the approaches
to overcome these drawbacks is by combining PLLA
materials to improve its properties or to generate new properties for a target application without developing new materials. Among
several methods of material modification, the
blending method, either solvent blending or melt blending, is simple and straightforward when compared to the
polymerization method for copolymer formation. Some studies have reported
blends of PLLA and other materials, such as blends of PLLA with other
crystalline polymers, i.e. PLLA with poly(ethylene oxide (PEO) (Lee et al.,
2012); PLLA with poly(D-lactic acid) (PDLA) (Ni’mah et al., 2014); PLLA with
other amorphous polymers, i.e. PLLA with atactic poly(methyl methacrylate)
(aPMMA) (Woo et al., 2014); PLLA with poly(vinyl phenol) (PVPh) (Ni’mah et al.,
2014); PLLA with elastomeric polymers such as natural rubber (Desa et al.,
2016; Nofar et al., 2019); PLLA with nanoparticles (Raquez et al., 2013); PLLA
with biodegradable and biomaterial such as chitosan (Duarte et al., 2010) or
cellulose (Ni’mah et al., 2017); and PLLA and plasticizers (Sitompul et al.,
2016). All those modifications were made to meet the specifically desired
properties for intended applications. PLLA has already been widely utilized in
many applications, such as packaging, and in environmental and biomedical
fields (Nofar et al. 2019).
Plasticizers have been reported to have been blended with PLLA to improve its mechanical properties (Sitompul et al., 2016). Plasticizers are additive materials that can increase the flexibility and durability of a material. For certain issues and applications, biodegradable plasticizers have become favored for use as PLLA modifiers. In biomedical applications, various PLLA blends have been investigated for application in drug delivery, implants, surgical sutures, orthopaedic devices and scaffolds in tissue engineering (Saini et al., 2016). For the last of these applications, some of the aspects that should be considered in using polyesters and their composites in tissue engineering are biodegradability, biocompatibility and morphology, as well as processability and the mechanical properties of the materials (Pavia et al., 2012). Some studies have reported the blending of PLLA with biopolymers, which have a plasticizing effect for biomedical applications. Chen et al. (2015) report the preparation of a porous scaffold from blend of PLLA and poly(ethylene glycol) (PEG) by supercritical CO2 foaming and particle leaching. The addition of PEG to the PLLA matrix has a plasticizing effect on the PLLA, indicated by the decrease in Tg in it. Another study by Frydrych et al. (2015) showed that blends of PLLA and poly(glycerol sebacate) (PGS) provide a porous microstructure, good hydrophilic characteristics, and good mechanical properties, which have potential for application as scaffolds in tissue engineering. PGS is a biodegradable and biocompatible synthetic elastomer, which shows mechanical behavior resembling the properties of soft tissue (Wang et al., 2002; Rai et al., 2012). PGS is also a non-toxic material and contains monomers of glycerol.
In blending two or more components, one of the problems that should be tackled is the low compatibility between two or more components, which will influence the physical properties of the composites. To enhance this compatibility, the addition of a compatibilizer is a simple approach that can be taken. The compatibilizer used can be one or all the components that have been surface-modified by the grafting technique. Wang et al. (2012) report that composites of MA-grafted PLLA and cellulose acetate have good mechanical properties and are biocompatible. MA is a non-toxic material which has been used in the biomedical field. In addition, for wood-plastic composites (blends of polypropylene and polyethylene), grafting MA onto the composite plastics has led to improvements in the mechanical properties of the composites because of the enhancement of interfacial bonding and dispersion of wood in the matrix (Gao et al., 2012).
In this study, glycerol (Gly) as a plasticizer was added to PLLA to improve its properties, including an increase in its flexibility and strength. The selected plasticizer is a miscible, biocompatible and biodegradable material. PLLA grafted with maleic anhydride (MA) (PLLA-g-MA) was also added to the PLLA/Gly blend as a compatibilizer. In the molecular structure of the composites, the addition of MA was expected to be able to increase the number of carbonyl groups that would perform specific bonding with other components, so that it could be used as a compatibilizer (Zhang & Sun, 2004). Therefore, the effects of the addition of PLLA-g-MA as a compatibilizer on the properties of the PLLA and PLLA/Gly blends were also investigated. To the best of our knowledge, no information is provided in the literature about the modification of PLLA with glycerol and PLLA-g-MA, so this study will contribute to research development in the polymer field.
Blend films of PLLA and glycerol with and without MA modification have been prepared and characterized in term of their properties. The physical properties, including thermal and mechanical ones, and the crystallinity of the films show improvement after the addition of glycerol, and further enhancement after the addition of compatibilizer (PLLA-g-MA). The decrease in tensile strength and Young’s modulus, and the increase in elongation at break for the composite films, show that they become softer and more flexible. The enhanced mechanical properties were caused by the improvement in interfacial bonding in the blend samples. Moreover, the morphology of the blend films displays a porous structure, which is similar to the characteristic three-dimensional structure of scaffolds in tissue engineering. Therefore, the biodegradable composite films with porous structures and excellent physical properties have the potential to be considered as scaffolds in tissue engineering applications, after further analysis has been conducted.
This work has been financially supported by a “Penelitian Pasca Doktor (Grant Number: 503/PKS/ITS/2017)” research grant for year 2017 from DRPM, Indonesia, to which the authors express their gratitude.
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