Investigation of the effect of nano-clay type on the non-isothermal crystallization kinetics and morphology of poly(3(R)-hydroxybutyrate) PHB/clay nanocomposites

The effects of PHB-g-MA types on the mechanical, thermal, morphological, structural, and rheological properties of polyhydroxybutyrate biopolymers

This study investigates the grafting of polyhydroxybutyrate (PHB) chains with maleic anhydride (MA) in concentrations ranging from 5 % to 10 % by weight. This process was conducted during microwave treatment and using a reactive extruder, employing benzoyl peroxide (BPO) as the initiator. The impact of these methods on PHB's overall properties was thoroughly investigated. In the study, PHB-g-MA was incorporated into neat PHB via the extrusion process at a 5 % loading rate. Notably, the mechanical properties exhibited an increase in the presence of PHB-g-MA, likely due to morphological improvements in the neat PHB, as indicated by morphological characterization. X-ray diffraction results indicated crystallinity percentages increase with the addition of MA. Differential scanning calorimetry revealed minimal variation in melting and crystallization temperatures when PHB-g-MA was included. Both storage and loss moduli were enhanced by the incorporation of PHB-g-MA, and the blends exhibited consistent tan delta values. Regarding rheological properties, the storage and loss moduli of PHB blends containing PHB-g-MA blends were observed to rise with rising frequency values. Based on these results, the microwave process was identified as the most effective method for grafting.

Approaches in Sustainable, Biobased Multilayer Packaging Solutions

The depletion of fossil resources and the growing demand for plastic waste reduction has put industries and academic researchers under pressure to develop increasingly sustainable packaging solutions that are both functional and circularly designed. In this review, we provide an overview of the fundamentals and recent advances in biobased packaging materials, including new materials and techniques for their modification as well as their end-of-life scenarios. We also discuss the composition and modification of biobased films and multilayer structures, with particular attention to readily available drop-in solutions, as well as coating techniques. Moreover, we discuss end-of-life factors, including sorting systems, detection methods, composting options, and recycling and upcycling possibilities. Finally, regulatory aspects are pointed out for each application scenario and end-of-life option. Moreover, we discuss the human factor in terms of consumer perception and acceptance of upcycling.

Crystallization of microbial polyhydroxyalkanoates: A review

Polyhydroxyalkanoates (PHAs), produced by the microbial fermentation, is a promising green polymer and has attracted much attention due to its excellent biocompatibility, complete biodegradability, and non-cytotoxicity. The physical properties of PHAs are closely related to their chemical and crystalline structure. Therefore, deep understanding and regulating the structure and crystallization of PHAs are the key factors to improve the performance of PHAs. This review first provides a brief overview of the development history, chemical structure, and basic properties of PHAs. Then, the crystal structure, crystal morphology, kinetics theories and crystallization behavior of nucleation-induced PHAs are systematically summarized to provide a theoretical foundation for improving PHAs crystallization rate and physical properties. In the end, the outlook on the crystallization and application prospects of PHAs is also addressed.

Microfibrillated Cellulose Grafted with Metacrylic Acid as a Modifier in Poly(3-hydroxybutyrate)

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.

Changes in Mechanical Properties of Polyhydroxyalkanoate with Double Silanized Cellulose Nanocrystals Using Different Organosiloxanes

Polyhydroxyalkanoate (PHA) is a biodegradable plastic with great potential for tackling plastic waste and marine pollution issues, but its commercial applications have been limited due to its poor processability. In this study, surface-modified cellulose nanocrystals were used to improve the mechanical properties of PHA composites produced via a melt-extrusion process. Double silanization was conducted to obtain hydrophobically treated CNC-based fillers, using tetraethyl orthosilicate (TEOS) and methyltrimethoxysilane (MTMS). The morphology, particle size distributions, and surface characteristics of the silanized CNCs and their compatibility with a PHA polymer matrix differed by the organosiloxane treatment and drying method. It was confirmed that the double silanized CNCs had hydrophobic surface characteristics and narrow particle size distributions, and thereby showed excellent dispersibility in a PHA matrix. Adding hydrophobically treated CNCs to form a PHA composite, the elongation at break of the PHA composites was improved up to 301%, with little reduction of Young's modulus, compared to pure PHA. Seemingly, the double silanized CNCs added played a similar role to a nucleation agent in the PHA composite. It is expected that such high ductility can improve the mechanical properties of PHA composites, making them more suitable for commercial applications.

Biodegradable Nanocomposite Microcapsules for Controlled Release of Urea

Urea is the most used fertilizer around the world as the main source of nitrogen to soil and plants. However, the administration of nitrogen dosage is critical, as its excess can be harmful to the environment. Therefore, the encapsulation of urea to achieve control on its release rates has been considered in several areas. In this work, encapsulation of urea by biodegradable polymer poly(3-hydroxybutyrate) (PHB) and its nanocomposites, namely PHB/MMT and PHB/OMMT, producing microcapsules by emulsion method is carried out. MMT and OMMT refer to Brazilian clays in a natural state and organophilized, respectively. In addition, the microcapsules are thus prepared to have their physicochemical characteristics investigated, then tested for biodegradation. Increment of microcapsules’ crystallinity due to the increased amount of poly(vinylacetate) (PVA), as emulsifier agent in the continuous phase, was confirmed by X-ray diffractometry (XRD) and atomic force microscopy (AFM). The presence of urea within microcapsules was verified by XRD, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The soil biodegradation assessments showed that PHB/OMMT microcapsules present higher degradation rates in sandy soils. The overall results suggest that the composites performed better than neat PHB and are very promising; moreover, PHB/OMMT microcapsules proved to be the best candidate for the controlled-release of urea in soils.

Fabrication and characterization of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) modified with nano-montmorillonite biocomposite

In this study, a poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) modified with nano-montmorillonite biocomposite (MMT/PHBH) was fabricated by solution-casting method. The results showed that the addition of MMT increased the crystallinity and the number of spherulites, which indicated that MMT was an effective nucleating agent for PHBH. The maximum decomposition peak of the biocomposites moved to a high temperature and residue presented an increasing trend. The biocomposites showed the best thermal stability at 1 wt% MMT. Compared with PHBH, 182.5% and 111.2% improvement in elastic modulus and tensile strength were obtained, respectively. Moreover, the oxygen permeability coefficient and the water vapor permeability of MMT/PHBH biocomposites decreased by 43.9% and 6.9%, respectively. It was also found that the simultaneous enhancements on the crystallizing, thermal stability, mechanical, and barrier properties of biocomposites were mainly caused by the formation of intercalated structure between PHBH and MMT.

Supernucleation, crystalline structure and thermal stability of bacterially synthesized poly(3-hydroxybutyrate) polyester tailored by thymine as a biocompatible nucleating agent

Naturally occurring thymine (TM) was incorporated into bacterial poly(3-hydroxybutyrate) (PHB) polyester to fabricate a novel and green biocomposite. Both 0.5% and 1% TM exhibit supernucleation effect on PHB, and crystallization kinetics suggests TM significantly increased T_c and X_c, and substantially shortened t_1/2 of PHB. Epitaxial nucleation caused by a perfect crystal lattice matching between PHB and TM, was proposed to elucidate nucleation mechanism of PHB. Hydrogen bond interaction exists between CO, C-O-C groups of PHB and -CH₃ (or -CH)/-NH- group of TM. TM interacted with CO group of PHB crystalline phase rather than that of amorphous one. In addition, two new IR crystalline bands assigned to C-O-C group of PHB appeared in the presence of TM, which arises from shift of two amorphous ones, respectively. TM enhanced onset thermal degradation temperature of PHB, mainly attributed to increased degree of crystallinity of PHB and flame retardance effect of TM.

Comparative Screening of the Structural and Thermomechanical Properties of FDM Filaments Comprising Thermoplastics Loaded with Cellulose, Carbon and Glass Fibers

Additive manufacturing (AM) has been rapidly growing for a decade in both consumer and industrial products. Fused deposition modeling (FDM), one of the most widely used additive manufacturing methods, owes its popularity to cost effectiveness in material and equipment investment. Current efforts are aimed toward high load-bearing capacity at low material costs. However, the mechanical reliability of end-products derived from these compositions and their dependence on microstructural effects, have remained as major limitations. This is mainly owing to the unknown mechanics of the materials, including the reinforcing or filler components and their interphase/interface compatibility. For this reason, here we investigate the most relevant commercial polymeric materials used in composite filaments, associated phases and the characterization protocols that can guide component selection, screening and troubleshooting. We first present thermal analyses (thermogravimetric, TGA and differential scanning calorimetry, DSC) in relation to the constituent fractions and identify the type of polymer for uses in filaments production. The influence of various fillers is unveiled in terms of the crystallization behavior of derived 3D-printed parts. To understand the microstructural effects on the material strength, we carry out a series of tensile experiments on 3-D printed dog-bone shaped specimens following ISO standards. Simultaneously, real-time thermal energy dissipation and damage analyses are applied by using infrared measurements at fast frame rates (200 Hz) and high thermal resolution (50 mK). The failure regions of each specimen are examined via optical, scanning and transmission electron microscopies. The results are used to reveal new insights into the size, morphology and distribution of the constituents and interphases of polymer filaments for FDM. The present study represents advancement in the field of composite filament fabrication, with potential impact in the market of additive manufacturing.

Effects of modified nanocrystalline cellulose on the hydrophilicity, crystallization and mechanical behaviors of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

An effective approach is developed to enhance the compatibility between the dispersed NCC and the PHBH matrix via surface grafting.

Third generation poly(hydroxyacid) composite scaffolds for tissue engineering

Bone tissue engineering based on scaffolds is quite a complex process as a whole gamut of criteria needs to be satisfied to promote cellular attachment, proliferation and differentiation: biocompatibility, right surface properties, adequate mechanical performance, controlled bioresorbability, osteoconductivity, angiogenic cues, and vascularization. Third generation scaffolds are more of composite types to maximize biological-mechanical-chemical properties. In the present review, our focus is on the performance of micro-organism-derived polyhydroxyalkanoates (PHAs)-polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV)-composite scaffolds with ceramics and natural polymers for tissue engineering applications with emphasis on bone tissue. We particularly emphasize on how material properties of the composites affect scaffold performance. PHA-based composites have demonstrated their biocompatibility with a range of tissues and their capacity to induce osteogenesis due to their piezoelectric properties. Electrospun PHB/PHBV fiber mesh in combination with human adipose tissue-derived stem cells (hASCs) were shown to improve vascularization in engineered bone tissues. For nerve and skin tissue engineering applications, natural polymers such as collagen and chitosan remain the gold standard but there is scope for development of scaffolds combining PHAs with other natural polymers which can address some of the limitations such as brittleness, lack of bioactivity and slow degradation rate presented by the latter. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1667-1684, 2017.