Infrared Spectroscopy and X-ray Diffraction Studies of Thermal Behavior and Lamella Structures of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(HB-co-HV)) with PHB-Type Crystal Structure and PHV-Type Crystal Structure

Mechanical, Thermal, and Physicochemical Properties of Filaments of Poly (Lactic Acid), Polyhydroxyalkanoates and Their Blend for Additive Manufacturing

Polymeric blends are employed in the production of filaments for additive manufacturing to balance mechanical and processability properties. The mechanical and thermal properties of polymeric filaments made of poly (lactic acid) (PLA), polyhydroxyalkanoates (PHA), and its blend (PLA-PHA) are investigated herein and correlated to their measured structural and physicochemical properties. PLA exhibits the highest stiffness and tensile strength, but lower toughness. The mechanical properties of the PLA-PHA blend were similar to those of PLA, but with a significantly higher toughness. Despite the lower mechanical properties of neat PHA, incorporating a small amount (12 wt.%) of PHA into PLA significantly enhances toughness (approximately 50%) compared to pure PLA. The synergistic effect is attributed to the spherulitic morphology of blended PHA in PLA, promoting interactions between the amorphous regions of both polymers. Thermal stability is notably improved in the PLA-PHA blend, as determined by thermogravimetric analysis. The blend also exhibits lower cold crystallization and glass transition temperatures as compared to PLA, which is beneficial for additive manufacturing. Following additive manufacturing, X-ray photoelectron spectroscopic showed that the three filaments present an increase in C-C and C=O bonds associated with the loss of C-O bonds. The thermal process induces a slight increase in crystallinity in PHA due to chain reorganization. The study provides insights into the thermal and structural changes occurring during the melting process of additive manufacturing.

The Structural Evolution of β-to-α Phase Transition in the Annealing Process of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

In this study, the structural and property changes induced in the highly ordered structure of preoriented poly(3-hydroxybutyrate-co-3-hydroxyvalerate) PHBV films containing the β-form during annealing were investigated. The transformation of the β-form was investigated by means of in situ wide-angle X-ray diffraction (WAXD) using synchrotron X-rays. The comparison of PHBV films with the β-form before and after annealing was performed using small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The evolution mechanism of β-crystal transformation was elucidated. It was revealed that most of the highly oriented β-form directly transforms into the highly oriented α-form, and there might be two kinds of transformations: (1) The β-crystalline bundles may be transformed one by one rather than one part by one part during annealing before a certain annealing time. (2) The β-crystalline bundles crack or the molecular chains of the β-form are separated from the lateral side after annealing after a certain annealing time. A model to describe the microstructural evolution of the ordered structure during annealing was established based on the results obtained.

Electrospun poly(3-hydroxybutyrate-co-3-hydroxyvalerate) scaffolds - a step towards ligament repair applications

The incidence of anterior cruciate ligament (ACL) ruptures is approximately 50 per 100,000 people. ACL rupture repair methods that offer better biomechanics have the potential to reduce long term osteoarthritis. To improve ACL regeneration biomechanically similar, biocompatible and biodegradable tissue scaffolds are required. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), with high 3-hydroxyvalerate (3HV) content, based scaffold materials have been developed, with the advantages of traditional tissue engineering scaffolds combined with attractive mechanical properties, e.g., elasticity and biodegradability. PHBV with 3HV fractions of 0 to 100 mol% were produced in a controlled manner allowing specific compositions to be targeted, giving control over material properties. In conjunction electrospinning conditions were altered, to manipulate the degree of fibre alignment, with increasing collector rotating speed used to obtain random and aligned PHBV fibres. The PHBV based materials produced were characterised, with mechanical properties, thermal properties and surface morphology being studied. An electrospun PHBV fibre mat with 50 mol% 3HV content shows a significant increase in elasticity compared to those with lower 3HV content and could be fabricated into aligned fibres. Biocompatibility testing with L929 fibroblasts demonstrates good cell viability, with the aligned fibre network promoting fibroblast alignment in the axial fibre direction, desirable for ACL repair applications. Dynamic load testing shows that the 50 mol% 3HV PHBV material produced can withstand cyclic loading with reasonable resilience. Electrospun PHBV can be produced with low batch variability and tailored, application specific properties, giving these biomaterials promise in tissue scaffold applications where aligned fibre networks are desired, such as ACL regeneration.   .

A Study of C=O…HO and OH…OH (Dimer, Trimer, and Oligomer) Hydrogen Bonding in a Poly(4-vinylphenol) 30%/Poly(methyl methacrylate) 70% Blend and its Thermal Behavior Using Near-Infrared Spectroscopy and Infrared Spectroscopy

Inter- and intramolecular hydrogen bonding and their temperature-dependent changes in a poly(4-vinylphenol)/poly(methyl methacrylate)(PVPh 30%/PMMA 70%) blend were investigated using near-infrared (NIR) and infrared (IR) spectroscopy. Band assignments of the fundamentals and first overtones of the OH stretching mode of a free OH group and OH groups in C=O···HO and OH···OH (dimer, trimer, and oligomer) hydrogen bonding of PVPh 30%/PMMA 70% were carried out by comparison between its NIR and IR spectra and comparison with NIR and IR spectra of phenol. The comparison of the NIR spectra of the PVPh 30%/PMMA 70% blend (hereafter, we denote it as PVPh30%) with the corresponding IR spectra reveals that to observe bands arising from the free OH and OH···OH dimer, which is a weaker hydrogen bonding, NIR is better while to investigate bands originating from OH groups in the OH···O=C and OH···OH (oligomer) hydrogen bonds, which are stronger hydrogen bonding, IR is better. Thus, a combination of IR and NIR spectroscopy has provided convincing results for the hydrogen bonding of PVPh30%. The relative intensity of the two bands at 7058 and 6921 cm^-1 (I₇₀₅₈/I₆₉₂₁) due to the first overtones of the OH stretching modes of the free OH group and the OH group in the dimer, respectively, increases significantly above 90 °C, which is close to Tg of PVPh. In concomitance with the intensity increase in the relative intensity of the free OH band, the intensity of a band at 1706 cm^-1 due to the C=O stretching mode of the C=O···HO hydrogen bond of PVPh30% decreases above 90°C. These results suggest that above the Tg of PVPh the C=O···HO hydrogen bond is broken gradually and that the free OH increases. Of note is that below Tg the intensities of NIR bands due to the OH first overtones of free OH group and OH groups in the OH···OH dimer gain intensity in parallel with temperature increase, and above Tg the intensity of the band derived from the OH···OH group increases linearly much slower than that of the band due to the free OH. Moreover, a band due to an OH···OH oligomer decreases linearly. Hence, it is very likely that the OH···OH oligomers dissociate into free OH groups. Anharmonicity of O-H bonds, which is sensitive to a hydrogen bond, was estimated for the free OH and OH bonds in the C=O···HO and OH···OH (dimer, trimer, and oligomer) hydrogen bonding by comparison between the NIR and IR spectra in the OH stretching band regions.

Effect of Polyhydroxyalkanoate (PHA) Concentration on Polymeric Scaffolds Based on Blends of Poly-L-Lactic Acid (PLLA) and PHA Prepared via Thermally Induced Phase Separation (TIPS)

Hybrid porous scaffolds composed of both natural and synthetic biopolymers have demonstrated significant improvements in the tissue engineering field. This study investigates for the first time the fabrication route and characterization of poly-L-lactic acid scaffolds blended with polyhydroxyalkanoate up to 30 wt%. The hybrid scaffolds were prepared by a thermally induced phase separation method starting from ternary solutions. The microstructure of the hybrid porous structures was analyzed by scanning electron microscopy and related to the blend composition. The porosity and the wettability of the scaffolds were evaluated through gravimetric and water contact angle measurements, respectively. The scaffolds were also characterized in terms of the surface chemical properties via Fourier transform infrared spectroscopy in attenuated total reflectance. The mechanical properties were analyzed through tensile tests, while the crystallinity of the PLLA/PHA scaffolds was investigated by differential scanning calorimetry and X-ray diffraction.

Accelerated Weathering Effects on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and PHBV/TiO2 Nanocomposites

The effect of accelerated weathering on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and PHBV-based nanocomposites with rutile titanium (IV) dioxide (PHBV/TiO₂) was investigated. The accelerated weathering test applied consecutive steps of UV irradiation (at 340 nm and 0.76 W m⁻² irradiance) and moisture at 50 °C following the ASTM D4329 standard for up to 2000 h of exposure time. The morphology, chemical structure, crystallization, as well as the mechanical and thermal properties were studied. Samples were characterized after 500, 1000, and 2000 h of exposure time. Different degradation mechanisms were proposed to occur during the weathering exposure and were confirmed based on the experimental data. The PHBV surface revealed cracks and increasing roughness with the increasing exposure time, whereas the PHBV/TiO₂ nanocomposites showed surface changes only after 2000 h of accelerated weathering. The degradation of neat PHBV under moisture and UV exposure occurred preferentially in the amorphous phase. In contrast, the presence of TiO₂ in the nanocomposites retarded this process, but the degradation would occur simultaneously in both the amorphous and crystalline segments of the polymer after long exposure times. The thermal stability, as well as the temperature and rate of crystallization, decreased in the absence of TiO₂. TiO₂ not only provided UV protection, but also restricted the physical mobility of the polymer chains, acting as a nucleating agent during the crystallization process. It also slowed down the decrease in mechanical properties. The mechanical properties were shown to gradually decrease for the PHBV/TiO₂ nanocomposites, whereas a sharp drop was observed for the neat PHBV after an accelerated weathering exposure. Atomic force microscopy (AFM), using the amplitude modulation–frequency modulation (AM–FM) tool, also confirmed the mechanical changes in the surface area of the PHBV and PHBV/TiO₂ samples after accelerated weathering exposure. The changes in the physical and chemical properties of PHBV/TiO₂ confirm the barrier activity of TiO₂ for weathering attack and its retardation of the degradation process.

A Study on Blend Ratio-dependent Far-IR and Low-frequency Raman Spectra and WAXD Patterns of Poly(3-hydroxybutyrate)/poly(4-vinylphenol) Using Homospectral and Heterospectral Two-dimensional Correlation Spectroscopy

An intensive analysis of far-infrared (far-IR), low-frequency Raman, and wide angle X-ray diffraction (WAXD) data has been performed by two-dimensional correlation spectroscopy (2D-COS) as a function of the blend ratio of poly(3-hydroxybutyrate)/poly(4-vinylphenol) (PHB/PVPh). Homospectral 2D-COS revealed that a weak band at 128 cm^-1 in the far-IR spectra appeared more clearly in the 2D correlation spectra. Heterospectral 2D-COS (far-IR/low-frequency Raman and far-IR/WAXD) provided very important results that were hardly detected in the conventional 2D-COS. A far-IR peak at 130 cm^-1 in the heterospectral 2D-COS had negative correlations with the peaks in the low-frequency Raman spectra at 81, 100, and 110 cm^-1 and WAXD profile 8.78 and 11.01°. These results indicated that those peaks have different origins; the 130 cm^-1 peak comes from the intermolecular C=O···H-O hydrogen bond between PHB and PVPh, while those for low-frequency Raman and WAXD peaks are the features of PHB crystalline structure.

Cationic Cyclopentadienyliron Complex as a Novel and Successful Nucleating Agent on the Crystallization Behavior of the Biodegradable PHB Polymer

Cationic cyclopentadienyliron (CpFe⁺) is one of the most fruitful organometallic moieties that has been utilized to mediate the facile synthesis of a massive number of macromolecules. However, the ability of this compound to function as a nucleating agent to improve other macromolecule properties has not been explored. This report scrutinizes the influence of the cationic complex as a novel nucleating agent on the spherulitic morphology, crystal structure, and isothermal and non-isothermal crystallization behavior of the Poly(3-hydroxybutyrate) (PHB) bacterial origin. The incorporation of the CpFe⁺ into the PHB materials caused a significant increase in its spherulitic numbers with a remarkable reduction in the spherulitic sizes. Unlike other nucleating agents, the SEM imageries exhibited a good dispersion without forming agglomerates of the CpFe⁺ moieties in the PHB matrix. Moreover, according to the FTIR analysis, the cationic organoiron complex has a strong interaction with the PHB polymeric chains via the coordination with its ester carbonyl. Yet, the XRD results revealed that this incorporation had no significant effect on the PHB crystalline structure. Though the CpFe⁺ had no effect on the polymer’s crystal structure, it accelerated outstandingly the melt crystallization of the PHB. Meanwhile, the crystallization half-times (t_0.5) of the PHB decreased dramatically with the addition of the CpFe⁺. The isothermal and non-isothermal crystallization processes were successfully described using the Avrami model and a modified Avrami model, as well as a combination of the Avrami and Ozawa methods. Finally, the effective activation energy of the PHB/CpFe⁺ nanocomposites was much lower than those of their pure counterparts, which supported the heterogeneous nucleation mechanism with the organometallic moieties, indicating that the CpFe⁺ is a superior nucleating agent for this class of polymer.

Rydberg transitions as a probe for structural changes and phase transition at polymer surfaces: an ATR-FUV-DUV and quantum chemical study of poly(3-hydroxybutyrate) and its nanocomposite with graphene

ATR-FUV-DUV (145–300 nm; 8.55–4.13 eV) and quantum mechanical calculations study of PHB and its nanocomposite with graphene.

C–H⋯O (ether) hydrogen bonding along the (110) direction in polyglycolic acid studied by infrared spectroscopy, wide-angle X-ray diffraction, quantum chemical calculations and natural bond orbital calculations

Polyglycolic acid (PGA), a biodegradable polyester with a simple molecular structure, shows an abnormally high melting point of 220 °C which is the highest among biopolyesters.

Estudo da miscibilidade das misturas de PHB e PLA, com um PHB de alta polidispersividade

Neste trabalho, foi estudada a miscibilidade de misturas de um PHB constituído de frações de alta e baixa massa molar com um PLA de alta massa molar. Os materiais extrudados foram analisados pelas técnicas de calorimetria exploratória diferencial (DSC), espectroscopia dielétrica (DE) e análises dinâmico-mecânicas (DMA). A partir dos resultados observou-se o distinto comportamento cristalino das frações de PHB, assim como a miscibilidade parcial do PLA com o PHB de baixa massa molar.

Poly(3-hydroxybutyrate) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate): Structure, Property, and Fiber

Poly(3-hydroxybutyrate) [P(3HB)] and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] are produced by various microorganisms as an intracellular carbon and energy reserve from agricultural feedstocks such as sugars and plant oils under unbalanced growth conditions. P(3HB) and P(3HB-co-3HV) have attracted the attention of academia and industry because of its biodegradability, biocompatibility, thermoplasticity, and plastic-like properties. This review first introduced the isodimorphism, spherulites, and molecular interaction of P(3HB) and P(3HB-co-3HV). In addition, the effects of 3HV content on the melting temperature and crystallization rate were discussed. Then the drawbacks of P(3HB) and P(3HB-co-3HV) including brittleness, narrow melt processing window, low crystallization rate, slow biodegradation rate in body, and so on were summarized. At last, the preparation, structure, and properties of P(3HB) and P(3HB-co-3HV) fiber were introduced.