Biopolymer‐based composites have attracted the attention of researchers and industries due to their eco‐friendliness and environmental sustainability, as well as their suitability for a number of applications. Biocomposites containing natural fibers and biopolymers would be the ideal choice in the development of biodegradable materials for different applications. Polylactic acid (PLA) is an environmentally interesting biopolymer, which also has exclusive qualities, such as good transparency and processability, glossy appearance, and high rigidity, although it has some shortcomings as well, for example, its brittleness and high rate of crystallization. PLA‐based natural fiber composites are entirely bio‐based materials with promising biodegradability and mechanical properties. Several research studies have been carried out on PLA and its composites to explore their potential to substitute petroleum‐based products, but until now there is no comprehensive review with up‐to‐date research data available in the literature. The aim of this review is to highlight the trends in the research and development of PLA and PLA‐based natural fiber composites over the past few years. This review article covers current research efforts on the synthesis and biodegradation of PLA, its properties, trends, challenges and prospects in the field of PLA and its composites. PLA‐based composites are moderately abundant; and further research and development is needed for cost reduction and broader utilization. POLYM. COMPOS., 40:446–463, 2019. © 2018 Society of Plastics Engineers

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Abstract:In this study, oil palm mesocarp fiber (OPMF) was treated with superheated steam (SHS) in order to modify its characteristics for biocomposite applications. Treatment was conducted at temperatures 190-230 °C for 1, 2 and 3 h. SHS-treated OPMF was evaluated for its chemical composition, thermal stability, morphology and crystallinity. OPMF treated at 230 °C exhibited lower hemicellulose content (9%) compared to the OPEN ACCESSMolecules 2013, 18 9133 untreated OPMF (33%). Improved thermal stability of OPMF was found after the SHS treatment. Moreover, SEM and ICP analyses of SHS-treated OPMF showed that silica bodies were removed from OPMF after the SHS treatment. XRD results exhibited that OPMF crystallinity increased after SHS treatment, indicating tougher fiber properties. Hemicellulose removal makes the fiber surface more hydrophobic, whereby silica removal increases the surface roughness of the fiber. Overall, the results obtained herewith suggested that SHS is an effective treatment method for surface modification and subsequently improving the characteristics of the natural fiber. Most importantly, the use of novel, eco-friendly SHS may contribute to the green and sustainable treatment for surface modification of natural fiber.

In this study, microcrystalline cellulose (MCC) was extracted from roselle fiber through acid hydrolysis treatment and its properties were compared with those of commercially available MCC. The physicochemical and morphological characteristics, elemental composition, size distribution, crystallinity and thermal properties of the obtained MCC were analyzed in this work. Fourier transform infrared spectroscopy (FTIR) analysis provided clear evidence that the characteristic peak of lignin was absent in the spectrum of the MCC prepared from roselle fiber. Rough surface and slight aggregation of MCC were observed by scanning electron microscopy (SEM). Energy dispersive X-ray (EDX) analysis showed that pure MCC with small quantities of residues and impurities was obtained, with a similar elemental composition to that of commercial MCC. A mean diameter of approximately 44.28μm was measured for MCC by using a particle size analyzer (PSA). X-ray diffraction (XRD) showed the crystallinity increased from 63% in roselle pulp to 78% in roselle MCC, the latter having a slightly higher crystallinity than that of commercial MCC (74%). TGA and DSC results indicated that the roselle MCC had better thermal stability than the roselle pulp, whereas it had poorer thermal stability in comparison with commercial MCC. Thus, the isolated MCC from roselle fibers will be going to use as reinforcing element in green composites and may be a precursor for future roselle derived nanocellulose, and thus a promising subject in nanocomposite research.

Natural fiber‐based polymer composites have been widely studied to substitute synthetic materials. In this research, pineapple leaf fibers (PALF) and coir fibers (CF) were loaded into a polylactic acid (PLA) matrix to develop composite materials with improved mechanical and thermal properties, which could be potentially applied as biodegradable food packaging. Biocomposites with different fiber ratios were manufactured using an internal mixer plasticizer and a hot press machine. Mechanical and thermal analyses of the obtained composites were carried out and the results were compared with those of pure PLA. Scanning electron microscopy (SEM) was used to observe the microstructural failure of the composites. Mechanical tests indicated that all the composites had higher tensile and flexural modulus, compared to those of neat PLA. Also, strength values were increased upon addition of PALF, while impact tests showed enhanced strength results upon addition of CF. SEM findings confirmed the outcomes of the mechanical tests. DMA results confirmed that the storage and loss moduli of the CF/PALF/PLA hybrid composites increased with respect to those of the neat PLA, whereas the tan δ decreased. The coefficient of thermal expansion (CTE) of the PLA composites decreased with the addition of fiber reinforcements. Based on the results achieved in this investigation, the hybrid composite containing CF and PALF in a 1:1 ratio (C1P1) presented the optimum set of mechanical properties and improved thermal stability, which make it suitable for applications such as food packaging and structure components to help reduce the environmental loads. POLYM. COMPOS., 40:2000–2011, 2019. © 2018 Society of Plastics Engineers

a b s t r a c tHighly selective transformation of poly[(R)-3-hydroxybutyric acid] (PHB) into trans-crotonic acid was achieved by thermal degradation using Mg compounds: MgO and Mg(OH) 2 as catalysts. Through catalytic action, not only the temperature and E a value of degradation were lowered by 40e50 C and 11e14 kJ mol À1 , respectively, but also significant changes in the selectivity of pyrolyzates were observed. Notably, Mg(OH) 2 showed nearly complete selectivity (w100%) to trans-crotonic acid. Kinetic analysis of TG profiles revealed that the catalytic thermal degradation of PHB was initiated by some random degradation reactions, followed by the unzipping b-elimination from crotonate chain-ends as a main process. It was suggested that the Mg catalysts promote the totality of the b-elimination reactions by acting throughout the beginning and main processes, resulting in a lowering in the degradation temperature and the completely selective transformation of PHB.

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Roselle fiber is a renewable and sustainable agricultural waste enriched with cellulose polysaccharides. The isolation of Nanocrystalline cellulose (NCC) from roselle-derived microcrystalline cellulose (MCC) is an alternative approach to recover the agricultural roselle plant residue. In the present study, acid hydrolysis with different reaction time was carried out to degrade the roselle-derived MCC to form NCC. The characterizations of isolated NCC were conducted through Fourier Transform Infrared Ray (FTIR), Transmission Electron Microscopy (TEM), Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Microscopy (AFM), Dynamic Light Scattering (DLS), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). As evaluated from the performed morphological investigations, the needle-like shape NCC nanostructures were observed under TEM and AFM microscopy studies, while irregular rod-like shape of NCC was observed under FESEM analysis. With 60min hydrolysis time, XRD analysis demonstrated the highest NCC crystallinity degree with 79.5%. In thermal analysis by TGA and DSC, the shorter hydrolysis time tended to produce NCC with higher thermal stability. Thus, the isolated NCC from roselle-derived MCC has high potential to be used in application of pharmaceutical and biomedical fields for nanocomposite fabrication.