Abstract
This work proposes a new method for obtaining poly(3-hydroxybutyrate) (PHB)/microfibrillated cellulose (MC) composites with more balanced properties intended for the substitution of petroleum-based polymers in packaging and engineering applications. To achieve this, the MC surface was adjusted by a new chemical route to enhance its compatibility with the PHB matrix: (i) creating active sites on the surface of MC with γ-methacryloxypropyltrimethoxysilane (SIMA) or vinyltriethoxysilane (SIV), followed by (ii) the graft polymerization of methacrylic acid (MA). The high efficiency of the SIMA-MA treatment and the lower efficiency in the case of SIV-MA were proven by the changes observed in the Fourier transform infrared FTIR spectra of celluloses. All modified celluloses and the PHB composites containing them showed good thermal stability close to the processing temperature of PHB. SIMA-modified celluloses acted as nucleating agents in PHB, increasing its crystallinity and favoring the formation of smaller spherulites. A uniform dispersion of SIMA-modified celluloses in PHB as a result of the good compatibility between the two phases was observed by scanning electron microscopy and many agglomerations of fibers in the composite with unmodified MC. The dual role of SIMA-MA treatment, as both compatibilizer and plasticizer, was pointed out by mechanical and rheological measurements. This new method to modify MC and obtain PHB/MC composites with more balanced stiffness–toughness properties could be a solution to the high brittleness and poor processability of PHB-based materials.
Highlights
Looking at the stress–strain curves of composites (Figure 9), one may observe that the reinforcing effect of microfibrillated cellulose (MC)-surface of MC with γ-methacryloxypropyltrimethoxysilane (SIMA)-methacrylic acid (MA) and MC-SIMA was not followed by a strong decrease inelongation at break, as is the case for MC-SIV-MA and in the literature [34]
Fourier transform infrared spectroscopy (FTIR) spectroscopy confirmed the high efficiency of the SIMA and SIMA-MA treatments and the low efficiency of the SIV-MA treatment
The good adhesion between SIMA-modified celluloses and PHB and their good dispersion, highlighted by Scanning Electron Microscopy (SEM), led to a significant improvement in the tensile strength and modulus in these composites; an opposite effect was noticed for PHB/MC-SIV-MA
Summary
Promising results have been obtained with poly-(3-hydroxybutyrate) (PHB), an aliphatic microbial polyester that shows similar mechanical and thermal properties to polypropylene with the added bonuses of better barrier properties and biodegradability [5]. Polymethacrylic acid was previously grafted on a few cellulosic substrates [23,24], especially for medical application, no attempt to modify cellulose with PMA for increased compatibility with PHB has been performed so far. This is the first attempt to pre-activate the cellulose surface with various silanes for better grafting of PMA and obtaining improved properties. The influence of modified celluloses on the morphology, thermal, and mechanical properties of PHB composites was studied
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