Influence of Epoxidized Canola Oil (eCO) and Cellulose Nanocrystals (CNCs) on the Mechanical and Thermal Properties of Polyhydroxybutyrate (PHB)-Poly(lactic acid) (PLA) Blends

Biodegradability Assessment of Prickly Pear Waste-Polymer Fibers under Soil Composting

Nowadays, solving the problems associated with environmental pollution is of special interest. Therefore, in this work, the morphology and thermal and mechanical properties of extruded fibers based on polylactic acid (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) added to prickly pear flour (PPF) under composting for 3 and 6 months were evaluated. The highest weight loss percentage (92 ± 7%) was obtained after 6-month degradation of the PLA/PBAT/PPF/CO/AA blend, in which PPF, canola oil (CO), and adipic acid (AA) were added. Optical and scanning electron microscopy (SEM) revealed structural changes in the fibers as composting time increased. The main changes in the absorption bands observed by Fourier transform infrared spectroscopy (FTIR) were related to the decrease in -C=O (1740 cm-1) and -C-O (1100 cm-1) groups and at 1269 cm-1, associated with hemicellulose in the blends with PPF. Differential scanning calorimetry (DSC) showed an increase in the cold crystallization and melting point with degradation time, being more evident in the fibers with PPF, as well as a decrease in the mechanical properties, especially Young's modulus. The obtained results suggest that PPF residues could promote the biodegradability of PLA/PBAT-based fiber composites.

Commercialization potential of agro-based polyhydroxyalkanoates biorefinery: A technical perspective on advances and critical barriers

The exponential increase in the use and careless discard of synthetic plastics has created an alarming concern over the environmental health due to the detrimental effects of petroleum based synthetic polymeric compounds. Piling up of these plastic commodities on various ecological niches and entry of their fragmented parts into soil and water has clearly affected the quality of these ecosystems in the past few decades. Among the many constructive strategies developed to tackle this global issue, use of biopolymers like polyhydroxyalkanoates as sustainable alternatives for synthetic plastics has gained momentum. Despite their excellent material properties and significant biodegradability, polyhydroxyalkanoates still fails to compete with their synthetic counterparts majorly due to the high cost associated with their production and purification thereby limiting their commercialization. Usage of renewable feedstocks as substrates for polyhydroxyalkanoates production has been the thrust area of research to attain the sustainability tag. This review work attempts to provide insights about the recent developments in the production of polyhydroxyalkanoates using renewable feedstock along with various pretreatment methods used for substrate preparation for polyhydroxyalkanoates production. Further, the application of blends based on polyhydroxyalkanoates, and the challenges associated with the waste valorization based polyhydroxyalkanoates production strategy is elaborated in this review work.

Combined effects of plasticizers and D-lactide content on the mechanical and morphological behavior of polylactic acid

Nowadays, research into environmentally friendly, renewable materials is the focus of materials science. One of the best candidates for these purposes is polylactic acid (PLA), whose properties are determined mainly by its D-lactide content. PLA is often plasticized to achieve proper toughness. Our aim was to investigate the combined effects of plasticizers and D-lactide content on PLA. We investigated two different plasticizers: oligomeric lactide acid (OLA) and dioctyl adipate (DOA). An internal mixer was used to prepare the compounds, and then sheets were prepared by hot pressing. After mechanical and morphological analyses, we found that tensile strength and modulus of neat PLAs and PLA-OLA compounds decreased almost linearly with increasing D-lactide content. The mechanical properties of PLA-DOA compounds depended far less on D-lactide content than in the case of PLA-OLA compounds. Plasticizers promote the crystallization of crystallizable PLAs by their chain mobilizing effect-we obtained a higher crystalline fraction. The latter effect reduces the impact of the plasticizing effect of plasticizers in the product. The compatibility and dispersibility of plasticizers also have a significant effect on the properties of the materials. OLA is more compatible with PLA than DOA, which resulted in better plasticization, but caused more defects in the crystallites, thus reducing the crystalline melting temperature, and so the processing temperature of the compound containing plasticizers.

Biodegradable Polylactic Acid-Polyhydroxyalkanoate-Based Nanocomposites with Bio-Hydroxyapatite: Preparation and Characterization

Biodegradable polymers play a significant role in medical applications, especially internal devices because they can be broken down and absorbed into the body without producing harmful degradation products. In this study, biodegradable polylactic acid (PLA)-polyhydroxyalkanoate (PHA)-based nanocomposites with various PHA and nano-hydroxyapatite (nHAp) contents were prepared using solution casting method. Mechanical properties, microstructure, thermal stability, thermal properties, and in vitro degradation of the PLA-PHA-based composites were investigated. PLA-20PHA/5nHAp was shown to give the desired properties so it was selected to investigate electrospinnability at different applied high voltages. PLA-20PHA/5nHAp composite shows the highest improvement of tensile strength at 36.6 ± 0.7 MPa, while PLA-20PHA/10nHAp composite shows the highest thermal stability and in vitro degradation at 7.55% of weight loss after 56 days of immersion in PBS solution. The addition of PHA in PLA-PHA-based nanocomposites improved elongation at break, compared to the composite without PHA. PLA-20PHA/5nHAp solution was successfully fabricated into fibers by electrospinning. All obtained fibers showed smooth and continuous fibers without beads with diameters of 3.7 ± 0.9, 3.5 ± 1.2, and 2.1 ± 0.7 µm at applied high voltages of 15, 20, and 25 kV, respectively.

Improving the Processability and Performance of Micronized Fiber-Reinforced Green Composites through the Use of Biobased Additives

Green composites made of bioplastics reinforced with natural fibers have gained considerable attention over recent years. However, the use of natural fibers in composites usually compromise some key properties, such as the impact strength and the processability of the final materials. In the present study, two distinct additives, namely an epoxidized linseed oil (ELO) and a sugar-based surfactant, viz. GlucoPure^® Sense (GPS), were tested in composite formulations of poly(lactic acid) (PLA) or poly(hydroxybutyrate) (PHB) reinforced with micronized pulp fibers. Both additives showed a plasticizing effect, which led to a decrease in the Young’s and flexural moduli and strengths. At the same time, the elongation and flexural strain at break were considerably improved on some formulations. The melt flow rate was also remarkably improved with the incorporation of the additives. In the PHB-based composites, an increment of 230% was observed upon incorporation of 7.5 wt.% ELO and, in composites based on PLA, an increase of around 155% was achieved with the introduction of 2.5 wt.% GPS. ELO also increased the impact strength to a maximum of 29 kJ m⁻², in formulations with PLA. For most composites, a faster degradation rate was observed on the formulations with the additives, reaching, in the case of PHB composites with GPS, a noteworthy weight loss over 75% under burial testing in compost medium at room temperature.

Hemicellulose Films from Curaua Fibers (Ananas erectifolius): Extraction and Thermal and Mechanical Characterization

With growing environmental concerns over synthetic polymers, natural polymeric materials, such as hemicellulose, are considered a good sustainable alternative. Curaua fibers could be an excellent source of biopolymer as they have a relatively high hemicellulose content (15 wt%) and only a small amount of lignin (7 wt%). In this work, hemicellulose was extracted by an alkaline medium using KOH and the influence of the alkali concentration, temperature, and time was studied. A hemicellulose film was produced by water casting and its mechanical, thermal, and morphological properties were characterized. The results show that the best method, which resulted in the highest hemicellulose yield and lowest contamination from lignin, was using 10% (w/v) KOH concentration, 25 °C, and time of 3 h. The hemicellulose film exhibited better thermal stability and elongation at break than other polymeric films. It also exhibited lower rigidity and higher flexibility than other biodegradable polymers, including polylactic acid (PLA) and polyhydroxybutyrate (PHB).

Poly(3-hydroxybutyrate) Nanocomposites with Cellulose Nanocrystals

Poly(3-hydroxybutyrate) (PHB) is one of the most promising substitutes for the petroleum-based polymers used in the packaging and biomedical fields due to its biodegradability, biocompatibility, good stiffness, and strength, along with its good gas-barrier properties. One route to overcome some of the PHB’s weaknesses, such as its slow crystallization, brittleness, modest thermal stability, and low melt strength is the addition of cellulose nanocrystals (CNCs) and the production of PHB/CNCs nanocomposites. Choosing the adequate processing technology for the fabrication of the PHB/CNCs nanocomposites and a suitable surface treatment for the CNCs are key factors in obtaining a good interfacial adhesion, superior thermal stability, and mechanical performances for the resulting nanocomposites. The information provided in this review related to the preparation routes, thermal, mechanical, and barrier properties of the PHB/CNCs nanocomposites may represent a starting point in finding new strategies to reduce the manufacturing costs or to design better technological solutions for the production of these materials at industrial scale. It is outlined in this review that the use of low-value biomass resources in the obtaining of both PHB and CNCs might be a safe track for a circular and bio-based economy. Undoubtedly, the PHB/CNCs nanocomposites will be an important part of a greener future in terms of successful replacement of the conventional plastic materials in many engineering and biomedical applications.

Poly(lactic acid)/Poly(3-hydroxybutyrate) Biocomposites with Differently Treated Cellulose Fibers

The growing concern about environmental pollution has generated an increased demand for biobased and biodegradable materials intended particularly for the packaging sector. Thus, this study focuses on the effect of two different cellulosic reinforcements and plasticized poly(3-hydroxybutyrate) (PHB) on the properties of poly(lactic acid) (PLA). The cellulose fibers containing lignin (CFw) were isolated from wood waste by mechanical treatment, while the ones without lignin (CF) were obtained from pure cellulose by acid hydrolysis. The biocomposites were prepared by means of a melt compounding-masterbatch technique for the better dispersion of additives. The effect of the presence or absence of lignin and of the size of the cellulosic fibers on the properties of PLA and PLA/PHB was emphasized by using in situ X-ray diffraction, polarized optical microscopy, atomic force microscopy, and mechanical and thermal analyses. An improvement of the mechanical properties of PLA and PLA/PHB was achieved in the presence of CF fibers due to their smaller size, while CFw fibers promoted an increased thermal stability of PLA/PHB, owing to the presence of lignin. The overall thermal and mechanical results show the great potential of using cheap cellulose fibers from wood waste to obtain PLA/PHB-based materials for packaging applications as an alternative to using fossil based materials. In addition, in situ X-ray diffraction analysis over a large temperature range has proven to be a useful technique to better understand changes in the crystal structure of complex biomaterials.

Valorization of Hemp Hurds as Bio-Sourced Additives in PLA-Based Biocomposites

Sourced from agricultural waste, hemp hurds are a low-cost renewable material with high stiffness; however, despite their potential to be used as low-cost filler in natural fiber reinforced polymer biocomposites, they are often discarded. In this study, the potential to add value to hemp hurds by incorporating them into poly(lactic acid) (PLA) biopolymer to form bio-based materials for packaging applications is investigated. However, as with many plant fibers, the inherent hydrophilicity of hemp hurds leads to inferior filler-matrix interfacial interactions, compromising the mechanical properties of the resulting biocomposites. In this study, two chemical treatments, alkaline (NaOH) and alkaline/peroxide (NaOH/H₂O₂) were employed to treat hemp hurds to improve their miscibility with poly(lactic acid) (PLA) for the formation of biocomposites. The effects of reinforcement content (5, 10, and 15 wt. %), chemical treatments (purely alkaline vs. alkaline/peroxide) and treatment cycles (1 and 3 cycles) on the mechanical and thermal properties of the biocomposites were investigated. The biocomposites of treated hemp hurd powder exhibited enhanced thermal stability in the temperature range commonly used to process PLA (130–180 °C). The biocomposites containing 15 wt. % hemp hurd powder prepared using a single-cycle alkaline/peroxide treatment (PLA/15APHH1) exhibited a Young’s modulus of 2674 MPa, which is 70% higher than that of neat PLA and 9.3% higher than that of biocomposites comprised of PLA containing the same wt. % of untreated hemp hurd powder (PLA/15UHH). Furthermore, the tensile strength of the PLA/15APHH1 biocomposite was found to be 62.6 MPa, which was 6.5% lower than that of neat PLA and 23% higher than that of the PLA/15UHH sample. The results suggest that the fabricated PLA/hemp hurd powder biocomposites have great potential to be utilized in green and sustainable packaging applications.

Polyhydroxyalkanoates biopolymers toward decarbonizing economy and sustainable future

Polymers are synonymous with the modern way of living. However, polymers with a large carbon footprint, especially those derived from nonrenewable petrochemical sources, are increasingly perceived as detrimental to the environment and a sustainable future. Polyhydroxyalkanoate (PHA) is a microbial biopolymer and a plausible alternative for renewable sources. However, PHA in its monomeric forms has very limited applications due to its limited flexibility, tensile strength, and moldability. Herein, the life cycle of PHA molecules, from biosynthesis to commercial utilization for diverse applications is discussed. For clarity, the applications of this bioplastic biocomposite material are further segregated into two domains, namely, the industrial sector and the medical sector. The industry sectors reviewed here include food packaging, textiles, agriculture, automotive, and electronics. High-value addition of PHA for a sustainable future can be foreseen in the medical domain. Properties such as biodegradability and biocompatibility make PHA a suitable candidate for decarbonizing biomaterials during tissue repair, organ reconstruction, drug delivery, bone tissue engineering, and chemotherapeutics.

Canola Oil based Poly(ester-ether-amide-urethane) Nanocomposite and Its Anti-Corrosive Coatings

The environmental and health hazards associated with petro-based chemicals have motivated the researchers to replace them partially or wholly with renewable resource-based polymers. Vegetable oils serve as an excellent alternative to this end as they are cost effective, eco-friendly, easily available and rich with functional groups amenable to chemical reactions. The aim of the research work is to prepare Canola oil [CANO] derived poly (ester–ether–amide–urethane) (CPEEUA) nanocomposite coating material using N,N-bis (2-hydroxyethyl) fatty amide [CFA] obtained from CANO, Lactic acid [LA], and reinforced with Fumed Silica [FS]. CPEEUA was obtained by esterification, etherification, and urethanation reactions and its structure was confirmed from FTIR and NMR spectral analyses. CPEEUA/FS coatings were found to be scratch resistant, flexible, well-adhered to mild steel panels, and hydrophobic with 2.0–2.5 kg scratch hardness, 150lb/inch impact resistance and >90° contact angle value. They exhibited good corrosion protection in 3.5 wt% NaCl solution as investigated by Potentiodynamic Polarization and Electrochemical Impedance tests. CPEEUA coatings are safe for usage up to 200 °C.

Enhanced polyhydroxybutyrate (PHB) production by newly isolated rare actinomycetes Rhodococcus sp. strain BSRT1-1 using response surface methodology

Poly-β-hydroxybutyrate (PHB) is a biodegradable polymer, synthesized as carbon and energy reserve by bacteria and archaea. To the best of our knowledge, this is the first report on PHB production by a rare actinomycete species, Rhodococcus pyridinivorans BSRT1-1. Response surface methodology (RSM) employing central composite design, was applied to enhance PHB production in a flask scale. A maximum yield of 3.6 ± 0.5 g/L in biomass and 43.1 ± 0.5 wt% of dry cell weight (DCW) of PHB were obtained when using RSM optimized medium, which was improved the production of biomass and PHB content by 2.5 and 2.3-fold, respectively. The optimized medium was applied to upscale PHB production in a 10 L stirred-tank bioreactor, maximum biomass of 5.2 ± 0.5 g/L, and PHB content of 46.8 ± 2 wt% DCW were achieved. Furthermore, the FTIR and ¹H NMR results confirmed the polymer as PHB. DSC and TGA analysis results revealed the melting, glass transition, and thermal decomposition temperature of 171.8, 4.03, and 288 °C, respectively. In conclusion, RSM can be a promising technique to improve PHB production by a newly isolated strain of R. pyridinivorans BSRT1-1 and the properties of produced PHB possessed similar properties compared to commercial PHB.

Biopolymer blends of polyhydroxybutyrate and polylactic acid reinforced with cellulose nanofibrils

Poly(lactic acid) (PLA) was used in an effort to enhance the mechanical properties of poly(hydroxybutyrate) (PHB) and the blends were reinforced with cellulose nanofibrils (CNF). The conventional and dynamic mechanical, morphological, thermal and rheological properties of the obtained composite blends were determined. The results showed that the mechanical properties of neat PHB noticeably increased attributable to the good interaction between the biopolymers and CNF from the scanning electron microscopy (SEM) characterization. Thermal stability of the neat PHB was improved by adding PLA, however differential scanning calorimetry results showed that PLA created enhanced thermal properties while adding CNFs did not provide any change in the composite thermal properties. Dynamic mechanical and rheological properties of the neat PHB generally improved with both PLA and CNFs, however, it decreased at high loadings of CNFs attributed to fiber aggregations and fiber pull-out in comparison to the low loading level of CNF.

Production of Polyhydroxybutyrate (PHB) and Factors Impacting Its Chemical and Mechanical Characteristics

Plastic pollution is fueling the grave environmental threats currently facing humans, the animal kingdom, and the planet. The pursuit of renewable resourced biodegradable materials commenced in the 1970s with the need for carbon neutral fully sustainable products driving important progress in recent years. The development of bioplastic materials is highlighted as imperative to the solutions to our global environment challenges and to the restoration of the wellbeing of our planet. Bio-based plastics are becoming increasingly sustainable and are expected to substitute fossil-based plastics. Bioplastics currently include both, nondegradable and biodegradable compositions, depending on factors including the origins of production and post-use management and conditions. Among the most promising materials being developed and evaluated is polyhydroxybutyrate (PHB), a microbial bioprocessed polyester belonging to the polyhydroxyalkanoate (PHA) family. This biocompatible and non-toxic polymer is biosynthesized and accumulated by a number of specialized bacterial strains. The favorable mechanical properties and amenability to biodegradation when exposed to certain active biological environments, earmark PHB as a high potential replacement for petrochemical based polymers such as ubiquitous high density polyethylene (HDPE). To date, high production costs, minimal yields, production technology complexities, and difficulties relating to downstream processing are limiting factors for its progression and expansion in the marketplace. This review examines the chemical, mechanical, thermal, and crystalline characteristics of PHB, as well as various fermentation processing factors which influence the properties of PHB materials.

Polyhydroxybutyrate Bioresins with High Thermal Stability by Cross-linking with Resorcinol Diglycidyl Ether

The development of sustainable materials by employing natural and nontoxic resources has been attracting much attention over the previous years. In this work, we discuss for the first time the chemical combination between resorcinol diglycidyl ether (RDGE), an aromatic biobased thermosetting monomer, and polyhydroxybutyrate (PHB), a bioderived and biodegradable thermoplastic polyester. By this combination, we aimed to associate the high thermal stability of RDGE with a toughening effect by the aliphatic chains of PHB. The investigations on the mechanism of the cross-linking reaction and on the structural connectivity between the two components were realized by Fourier transform infrared (FTIR) and NMR spectroscopies. We found that the epoxide polymerization catalyzed by tertiary amines triggers the formation of crotonyl species by polyhydroxybutyrate cleavage. Two-dimensional NMR experiments show that polyhydroxybutyrate fragments covalently bind as side chains to the rigid aromatic network of the epoxide frame. The cross-linking between the two systems entails the formation of new ester and ether bonds. The obtained structures show a network homogeneity confirmed by a single T_g, from 85 to 47 °C, as a function of the formulation, and tan δ values from 87 to 53 °C. The combination of the two comonomers showed a positive effect. The PHB increased the toughness of RDGE-based thermosets, improving the material elasticity by increasing the chain length between the cross-links. An important result of this study is the high thermal stability of RDGE/PHB bioresins, with the T_5% varying between 330 and 310 °C as a function of the PHB ratio.

Flexible and Stretchable Temperature Sensors Fabricated Using Solution-Processable Conductive Polymer Composites

Accurate monitoring of physiological temperatures is important for the diagnosis and tracking of various medical conditions. This work presents the design, fabrication, and characterization of temperature sensors using conductive polymer composites (CPCs) patterned on both flexible and stretchable substrates through both drop coating and direct ink writing (DIW). These composites were formed using a high melting point biopolymer polyhydroxybutyrate (PHB) as the matrix and the graphenic nanomaterial reduced graphene oxide (rGO) as the nanofiller (from 3 to 12 wt%), resulting in a material that exhibits a temperature-dependent resistivity. At room temperature the composites exhibited electrical percolation behavior. Around the percolation threshold, both the carrier concentration and mobility were found to increase sharply. Sensors were fabricated by drop-coating PHB-rGO composites onto ink-jet printed silver electrodes. The temperature coefficient of resistance was determined to be 0.018 /°C for pressed rGO powders and 0.008 /°C for the 3 wt% samples (the highest responsivity of all composites). Composites were found to have good selectivity to temperature with respect to pressure and moisture. Thermal mapping was demonstrated using 6 × 7 arrays of sensing elements. Stretchable devices with a meandering pattern were fabricated using DIW, demonstrating the potential for these materials in healthcare monitoring devices.

Effects of Cellulose Nanocrystals and Cellulose Nanofibers on the Structure and Properties of Polyhydroxybutyrate Nanocomposites

One of the major obstacles for polyhydroxybutyrate (PHB), a biodegradable and biocompatible polymer, in commercial applications is its poor elongation at break (~3%). In this study, the effects of nanocellulose contents and their types, including cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs) on the crystallization, thermal, and mechanical properties of PHB composites were systematically compared. We explored the toughening mechanisms of PHB by adding CNCs and cellulose CNFs. The results showed that when the morphology of bagasse nanocellulose was rod-like and its content was 1 wt %, the toughening modification of PHB was the best. Compared with pure PHB, the elongation at break and Young’s modulus increased by 91.2% and 18.4%, respectively. Cellulose nanocrystals worked as heterogeneous nucleating agents in PHB and hence reduced its crystallinity and consequently improved the toughness of PHB. This simple approach could potentially be explored as a strategy to extend the possible applications of this biopolymer in packaging fields.

Amine Responsive Poly(lactic acid) (PLA) and Succinic Anhydride (SAh) Graft-Polymer: Synthesis and Characterization

Amines are known to react with succinic anhydride (SAh), which in reactions near room temperature, undergoes a ring opening amidation reaction to form succinamic acid (succinic acid-amine). In this work, we propose to form an amine-responsive polymer by grafting SAh to a poly(lactic acid) (PLA) backbone, such that the PLA can provide chemical and mechanical stability for the functional SAh during the amidation reaction. Grafting is performed in a toluene solution at mass content from 10 wt% to 75 wt% maleic anhydride (MAh) (with respect to PLA and initiator), and films are then cast. The molecular weight and thermal properties of the various grafted polymers are measured by gel permeation chromatography and differential scanning calorimetry, and the chemical modification of these materials is examined using infrared spectroscopy. The efficiency of the grafting reaction is estimated with thermogravimetric analysis. The degree of grafting is determined to range from 5% to 42%; this high degree of grafting is desirable to engineer an amine-responsive material. The response of the graft-polymers to amines is characterized using X-ray photoelectron spectroscopy, infrared spectroscopy, and differential scanning calorimetry. Changes in the chemical and thermal properties of the graft-polymers are observed after exposure to the vapors from a 400 ppm methylamine solution. In contrast to these changes, control samples of neat PLA do not undergo comparable changes in properties upon exposure to methylamine vapor. In addition, the PLA-g-SAh do not undergo changes in structure when exposed to vapors from deionized water without amines. This work presents potential opportunities for the development of real-time amine sensors.