FT-IR imaging spectroscopy of phase separation in blends of poly(3-hydroxybutyrate) with poly(L-lactic acid) and poly(epsilon-caprolactone)

Cellulose-based polypropoxy ether carboxylates as highly compatible, effective, and migration-resistant plasticizers for poly (lactic acid)

The utilization of cellulose for enhancing the strength, the PLA has received significant attention, however, poor interfacial compatibility of solid cellulose with PLA matrix still hinders their broader application. Herein, highly compatible cellulose-based polypropoxy ether carboxylates (CPPEC) were firstly manufactured via propoxylation of cellulose and following esterification with acetic acid, butyric acid, as well as oleic acid, respectively. Liquid CPPEC delivered excellent performances to PLA, especially, the values of elongation at break and low-temperature resistance of PLA blended with cellulose-based polypropoxy ether acetate (PLA/CPPEA) were respectively increased by 630.9 % and 146.3 % compared with those of neat PLA due to the synergistic effect of propyl and methyl groups in CPPEC with PLA matrix. Additionally, migration resistance of PLA/CPPEA increased 14.3 and 11.2 times, respectively, compared with those of PLA specimens blended with epoxidized soybean oil and dioctyl phthalate. All findings suggest that the CPPEC is suitable for large-scale application in the PLA industry.

Explication of mechanism governing atmospheric degradation of 3D-printed poly(lactic acid) (PLA) with different in-fill pattern and varying in-fill density

With the popularity of 3D-printing technology, poly(lactic acid) (PLA) has become a very good option for layer by layer printing as it is easy to handle, environment friendly, has low costs and most importantly, it is highly adaptable to different materials including carbon, nylon and some other fibres. PLA is an aliphatic poly-ester that is 100% bio-based and is bio-degradable as well. It is one of the rare bio-polymers to compete with traditional polymers in terms of performance and environmental impact. However, PLA is sensitive to water and susceptible to degradation under natural conditions of ultra-violet rays (UV), humidity, fumes, etc. There are many reports on the bio-degradation and photo-degradation of PLA which deal with the accelerated weathering test. However, the accelerated weathering test instruments lack the ability to correlate the stabilities maintained by the test with the actual occurrences during natural exposure. Thus, an attempt has been made in the present work to expose the 3D-printed PLA samples to actual atmospheric conditions of Aurangabad city (M.S.) in India. The degradation of PLA after the exposure is studied and a mechanism is elucidated. Additionally, the tensile properties of the PLA samples are evaluated to correlate the extent of degradation and the material performance. It was found that though the performance of PLA deteriorates with the exposure time, the combination of in-fill pattern and volume plays an important role on the tensile properties and the extent of degradation. It is concluded herein that with natural exposure, the degradation of PLA occurs in two stages, supported by a side reaction. Thus, this study offers a new perspective towards the life of components in actual application by exposing PLA to the natural atmosphere and evaluating its strength and structure.

Polyhydroxybutyrate blends: A solution for biodegradable packaging?

Poly (3-hydroxybutyrate) (PHB) is a valuable bio-based and biodegradable polymer that may substitute common polymers in packaging and biomedical applications provided that the production cost is reduced and some properties improved. Blending PHB with other biodegradable polymers is the most simple and accessible route to reduce costs and to improve properties. This review provides a comprehensive overview on the preparation, properties and application of the PHB blends with other biodegradable polyesters such as medium-chain-length polyhydroxyalkanoates, poly(ε-caprolactone), poly(lactic acid), poly(butylene succinate), poly(propylene carbonate) and poly (butylene adipate-co-terephthalate) or polysaccharides and their derivatives. A special attention has been paid to the miscibility of PHB with these polymers and the compatibilizing methods used to improve the dispersion and interface. The changes in the PHB morphology, thermal, mechanical and barrier properties induced by the second polymer have been critically analyzed in view of industrial application. The biodegradability and recyclability strategies of the PHB blends were summarized along with the processing techniques adapted to the intended application. This review provides the tools for a better understanding of the relation between the micro/nanostructure of PHB blends and their properties for the further development of PHB blends as solutions for biodegradable packaging.

A Review on Biological Synthesis of the Biodegradable Polymers Polyhydroxyalkanoates and the Development of Multiple Applications

Polyhydroxyalkanoates, or PHAs, belong to a class of biopolyesters where the biodegradable PHA polymer is accumulated by microorganisms as intracellular granules known as carbonosomes. Microorganisms can accumulate PHA using a wide variety of substrates under specific inorganic nutrient limiting conditions, with many of the carbon-containing substrates coming from waste or low-value sources. PHAs are universally thermoplastic, with PHB and PHB copolymers having similar characteristics to conventional fossil-based polymers such as polypropylene. PHA properties are dependent on the composition of its monomers, meaning PHAs can have a diverse range of properties and, thus, functionalities within this biopolyester family. This diversity in functionality results in a wide array of applications in sectors such as food-packaging and biomedical industries. In order for PHAs to compete with the conventional plastic industry in terms of applications and economics, the scale of PHA production needs to grow from its current low base. Similar to all new polymers, PHAs need continuous technological developments in their production and material science developments to grow their market opportunities. The setup of end-of-life management (biodegradability, recyclability) system infrastructure is also critical to ensure that PHA and other biobased biodegradable polymers can be marketed with maximum benefits to society. The biobased nature and the biodegradability of PHAs mean they can be a key polymer in the materials sector of the future. The worldwide scale of plastic waste pollution demands a reformation of the current polymer industry, or humankind will face the consequences of having plastic in every step of the food chain and beyond. This review will discuss the aforementioned points in more detail, hoping to provide information that sheds light on how PHAs can be polymers of the future.

Cell wall polymer distribution in bamboo visualized with in situ imaging FTIR

To better understand the high recalcitrance of bamboo during bioconversion, the fine spatial distribution of polymers in bamboo was studied with Imaging FTIR microscopy under both transmission and ATR modes, combined with PCA data processing. The results demonstrated that lignin, xylan and hydroxycinnamic acid (HCA) were more concentrated in the fibers near the xylem conduit, while cellulose was evenly distributed across the whole fiber sheath. PCA processing produced a clear separation between bamboo fibers and parenchyma cells, indicating that the parenchyma cells contains more pectin and HCA than fibers. It also demonstrated that cellulose, xylan and S-lignin were concentrated most heavily in bamboo fiber secondary cell walls, while G-lignin, pectin and HCA were found more in the compound middle lamella. The revealed information regarding polymer distribution is of great significance for better understanding of the inherent design mechanism of plant cell wall and its efficient utilization.

Effect of ultrahigh-pressure treatment on the functional properties of poly(lactic acid)/ZnO nanocomposite food packaging film

BACKGROUND

Our living environment is being increasingly polluted by petroleum-based plastics and there is an increasing demand for biodegradable food packaging. In this study, the effect of various ultrahigh-pressure (UHP) treatments (0, 200 and 400 MPa) on the microstructure and thermal, barrier and mechanical properties of poly(lactic acid) (PLA)/ZnO nanocomposite films was studied.

RESULTS

The film-forming solution was processed using UHP technology. The crystallinity, strength and stiffness of the composite film after UHP treatment increased. In addition, barrier property analysis showed that the UHP treatment significantly (P < 0.05) reduced the oxygen permeability and water vapor permeability (WVP) coefficient of the PLA/ZnO nanocomposite film. Furthermore, the WVP value of the film treated at 400 MPa (50 g kg^-1 nano-ZnO content) was the lowest and reduced by 47.3% compared with that of pure PLA film. The improvement in these properties might be due to the interaction between nano-ZnO and PLA matrix promoted by UHP treatment.

CONCLUSIONS

Therefore, the application of UHP technology on the film-forming solution could improve the crystallinity and functional properties of the nanocomposite film, and has great potential in the production of food packaging films with ideal functions. © 2021 Society of Chemical Industry.

Visualization of Inter- and Intramolecular Interactions in Poly(3-hydroxybutyrate)/Poly(L-lactic acid) (PHB/PLLA) Blends During Isothermal Melt Crystallization Using Attenuated Total Reflection Fourier Transform infrared (ATR FT-IR) Spectroscopic Imaging

Inter- and intramolecular interactions in multicomponent polymer systems influence their physical and chemical properties significantly and thus have implications on their synthesis and processing. In the present study, chemical images were obtained by plotting the peak position of a spectral band from the data sets generated using in situ attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopic imaging. This approach was successfully used to visualize changes in intra- and intermolecular interactions in poly(3-hydroxybutyrate)/poly(L-lactic acid) (PHB/PLLA) blends during the isothermal melt crystallization. The peak position of ν(C＝O) band, which reflects the nature of the intermolecular interaction, shows that the intermolecular interactions between PHB and PLLA in the miscible state (1733 cm^-1) changes to the inter- and intramolecular interaction (CH₃⋯O=C, 1720 cm^-1) within PHB crystal during the isothermal melt crystallization. Compared with spectroscopic images obtained by plotting the distribution of absorbance of spectral bands, which reveals the spatial distribution of blend components, the approach of plotting the peak position of a spectral band reflects the spatial distribution of different intra- and intermolecular interactions. With the process of isothermal melt-crystallization, the disappearance of the intermolecular interaction between PHB and PLLA and the appearance of the inter- and intramolecular interactions within the PHB crystal were both visualized through the images based on the observation of the band position. This work shows the potential of using in-situ ATR FT-IR spectroscopic imaging to visualize different types of inter- or intramolecular interactions between polymer molecules or between polymer and other additives in various types of multicomponent polymer systems.

Effect of Graphene Oxide on the Properties of Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate)

The main shortcomings of polyhydroxybutyrate (PHB), which is a biodegradable and biocompatible polymer used for biomedical and food packaging applications, are its low thermal stability, poor impact resistance and lack of antibacterial activity. This issue can be improved by blending with other biodegradable polymers such as polyhydroxyhexanoate to form poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), which is a copolymer with better impact strength and lower melting point. However, PHBHHx shows reduced stiffness than PHB and poorer barrier properties against moisture and gases, which is a drawback for use in the food industry. In this regard, novel biodegradable PHBHHx/graphene oxide (GO) nanocomposites have been prepared via a simple, cheap and environmentally friendly solvent casting method to enhance the mechanical properties and antimicrobial activity. The morphology, mechanical, thermal, barrier and antibacterial properties of the nanocomposites were assessed via several characterization methods to show the enhancement in the biopolymer properties. The stiffness and strength of the biopolymer were enhanced up to 40% and 28%, respectively, related to the strong matrix-nanofiller interfacial adhesion attained via hydrogen bonding interactions. Moreover, the nanocomposites showed superior thermal stability (as far as 40 °C), lower water uptake (up to 70%) and better gas and vapour barrier properties (about 45 and 35% reduction) than neat PHBHHx. They also displayed strong biocide action against Gram positive and Gram negative bacteria. These bio-based nanocomposites with antimicrobial activity offer new perspectives for the replacement of traditional petroleum-based synthetic polymers currently used for food packaging.

How does high-pressure CO2 affect the morphology of PCL/PLA blends? Visualization of phase separation using in situ ATR-FTIR spectroscopic imaging

Studies of phase separation in lower critical solution temperature (LCST) polymer blends exposed to high-pressure CO₂ provide an insight to their physical properties. Through using in situ high-pressure ATR-FTIR spectroscopic imaging, this work visualized the dynamic process of phase separation in Polycaprolactone (PCL)/Poly (lactic acid) (PLA) blend under high-pressure CO₂ for the first time. ATR-FTIR spectroscopic images revealed that phase separation in PCL/PLA blends occurs with increasing temperature or upon exposure to high-pressure CO₂. The change in the morphology of PCL-rich and PLA-rich domains in the ATR-FTIR spectroscopic images can be used to compare the extent of phase separation under different conditions. It is found that the extent of phase separation in PCL/PLA blends under high-pressure CO₂ is enhanced with increasing temperature, CO₂ pressure and exposure time. The effect of different molecular weights of one blend component, PCL, on the phase separation in PCL/PLA blends was also studied. This pioneering methodology opens possibilities to visualize the process of phase separation in LCST polymer blend systems and it can also be applied to study the process of interdiffusion in upper critical solution temperature (UCST) polymer blends.

Poly(trimethylene carbonate-co-valerolactone) copolymers are materials with tailorable properties: from soft to thermoplastic elastomers

Aliphatic poly(ester-carbonates) are receiving extensive research attention as tailorable materials suitable for multiple applications from tissue engineering and 3D scaffold printing to drug delivery. Thus, simple reliable procedures for producing easily tailorable poly(ester-carbonates) without metal residues are continuously sought after. In this work, we report on one-pot synthesis of random copolymers of TMC and δ-VL using metal-free biocompatible 1,5,7-triazabicyclo[4.4.0]dec-5-ene as a catalyst and benzyl alcohol and poly(ethylene oxide) as initiators. Random poly(ester-carbonates) with TMC : VL unit ratios ranging from 80 : 20 to 20 : 80 were synthesized via ring-opening polymerization while displaying excellent agreement of comonomers' ratios in the feed and copolymer chains. The copolymers' supramolecular structure, thermal and mechanical properties were thoroughly analyzed by various methods. The obtained results clearly indicated that the physicochemical properties can be controlled simply by varying the ratio of comonomers and the length of segments in the copolymer chain. Several copolymers exhibited behavior of thermoplastic elastomers with the most promising one exhibiting a 2200% increase in elongation at break compared to the poly(valerolactone) homopolymer while retaining tensile strength and Young's modulus suitable for biomedical applications. Overall, our work contributed to widening the portfolio of tailorable copolymers for specialized bioapplications and possibly paving a way for the use of more sustainable polymers in the biomedical field.

Fabrication and characterization of biodegradable PHBV/SiO2 nanocomposite for thermo-mechanical and antibacterial applications in food packaging

In the present study, biogenic silica nanoparticles (bSNPs) were synthesized from groundnut shells, and thoroughly characterized to understand its phase, and microstructure properties. The biopolymer was synthesized from yeast Wickerhamomyces anomalus and identified as Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) by GC-MS and NMR analysis. The bSNPs were reinforced to fabricate PHBV/SiO₂ nanocomposites via solution casting technique. The fabricated PHBV/SiO₂ nanocomposites revealed intercalated hybrid interaction between the bSNPs and PHBV matrix through XRD analysis. PHBV/SiO₂ nanocomposites showed significant improvement in physical, chemical, thermo-mechanical and biodegradation properties as compared to the bare PHBV. The cell viability study revealed excellent biocompatibility against L929 mouse fibroblast cells. The antibacterial activity of PHBV/SiO₂ nanocomposites was found to be progressively improved upon increasing bSNPs concentration against E. coli and S. aureus.

Studies on Chemical IR Images of Poly(hydroxybutyrate⁻co⁻hydroxyhexanoate)/Poly(ethylene glycol) Blends and Two-Dimensional Correlation Spectroscopy

Biodegradable poly-[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoates] (PHBHx) have been widely studied for their applications in potentially replacing petroleum-based thermoplastics. In this study, the effect of the high molecular weight (Mn = 3400) poly(ethylene glycol) (PEG) blended in the films of PHBHx with different ratios of PEG was investigated using chemical FTIR imaging. Chemical IR images and FTIR spectra measured with increasing temperature revealed that PEG plays an important role in changing the kinetics of PHBHx crystallization. In addition, two-dimensional correlation spectra clearly showed that thermal properties of PHBHx/PEG blend film changed when the blending ratio of PHBHx/PEG were 60/40 and 50/50. Consequently, PEG leads to changes in the thermal behavior of PHBHx copolymers.

Investigation of phase separated polyimide blend films containing boron nitride using FTIR imaging

Immiscible aromatic polyimide (PI) blend films and a PI blend film incorporated with thermally conductive boron nitride (BN) were prepared, and their phase separation behaviors were examined by optical microscopy and FTIR imaging. The 2,2'-bis(trifluoromethyl)benzidine (TFMB)-containing and 4,4'-thiodianiline (TDA)-containing aromatic PI blend films and a PI blend/BN composite film show two clearly separated regions; one region is the TFMB-rich phase, and the other region is the TDA-rich phase. The introduction of BN induces morphological changes in the immiscible aromatic PI blend film without altering the composition of either domain. In particular, the BN is selectively incorporated into the TDA-rich phase in this study.

Identification of trace additives in polymer materials by attenuated total reflection Fourier transform infrared mapping coupled with multivariate curve resolution

Although multivariate curve resolution (MCR) has been applied to the analysis of Fourier transform infrared (FTIR) imaging, it is still problematic to determine the number of components. The reported methods at present tend to cause the components of low concentration missed. In this paper a new idea was proposed to resolve this problem. First, MCR calculation was repeated by increasing the number of components sequentially, then each retrieved pure spectrum of as-resulted MCR component was directly compared with a real-world pixel spectrum of the local high concentration in the corresponding MCR map. One component was affirmed only if the characteristic bands of the MCR component had been included in its pixel spectrum. This idea was applied to attenuated total reflection (ATR)/FTIR mapping for identifying the trace additives in blind polymer materials and satisfactory results were acquired. The successful demonstration of this novel approach opens up new possibilities for analyzing additives in polymer materials.

Partial and Complete Wetting in Ultralow Interfacial Tension Multiphase Blends with Polylactide

The control of phase structuring in multiphase blends of polylactide (PLA) with other polymers is a viable approach to promote its broader implementation. In this article, ternary and quaternary blends of PLA with poly(butylene succinate) (PBS), poly(butylene adipate-co-terephthalate) (PBAT), and poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) are prepared by melt blending. The interfacial tensions between components are measured using three different techniques, and a Fourier transform infrared imaging technique is developed for the purpose of unambiguous phase identification. A tricontinuous complete wetting behavior is observed for the ternary 33PLA/33PBS/33PBAT blend before and after quiescent annealing, which correlates closely with spreading theory analysis. In the quaternary PLA/PBS/PBAT/PHBV blend, a concentration-dependent wetting behavior is found. At 10 vol % PBAT, self-assembled partially wet droplets of PBAT are observed at the interface of PBS and PHBV, and they remain stable after quiescent annealing as predicted by spreading theory. In contrast, at 25 vol % PBAT, a quadruple continuous system is observed after mixing, which only transforms to partially wet PBAT droplets after subsequent annealing. These results clearly indicate the potential of composition control during the mixing of multiphase systems to result in a complete change of spreading behavior.

Optical Autocatalysis Establishes Novel Spatial Dynamics in Phase Separation of Polymer Blends during Photocuring

We report a fundamentally new nonlinear dynamic system that couples optical autocatalytic behavior to phase evolution in photoreactive binary polymer blends. Upon exposure to light, the blend undergoes spontaneous patterning into a dense arrangement of microscale polymer filaments. The filaments' growth in turn induces local spinodal decomposition of the blend along their length, thereby regulating the spatially dynamics of phase separation. This leads to the spontaneous organization of a large-scale binary phase morphology dictated by the filament arrangement. This is a new mechanism for polymer blend organization, which couples nonlinear optical dynamics to chemical phase separation dynamics, and offers a new approach to light-directed patterning and organization of polymer and hybrid blends.

FTIR spectroscopic imaging and mapping with correcting lenses for studies of biological cells and tissues

Histopathology of tissue samples is used to determine the progression of cancer usually by staining and visual analysis. It is recognised that disease progression from healthy tissue to cancerous is accompanied by spectral signature changes in the mid-infrared range. In this work, FTIR spectroscopic imaging in transmission mode using a focal plane array (96 × 96 pixels) has been applied to the characterisation of Barrett's oesophageal adenocarcinoma. To correct optical aberrations, infrared transparent lenses were used of the same material (CaF₂) as the slide on which biopsies were fixed. The lenses acted as an immersion objective, reducing scattering and improving spatial resolution. A novel mapping approach using a sliding lens is presented where spectral images obtained with added lenses are stitched together such that the dataset contained a representative section of the oesophageal tissue. Images were also acquired in transmission mode using high-magnification optics for enhanced spatial resolution, as well as with a germanium micro-ATR objective. The reduction of scattering was assessed using k-means clustering. The same tissue section map, which contained a region of high grade dysplasia, was analysed using hierarchical clustering analysis. A reduction of the trough at 1077 cm⁻¹ in the second derivative spectra was identified as an indicator of high grade dysplasia. In addition, the spatial resolution obtained with the lens using high-magnification optics was assessed by measurements of a sharp interface of polymer laminate, which was also compared with that achieved with micro ATR-FTIR imaging. In transmission mode using the lens, it was determined to be 8.5 μm and using micro-ATR imaging, the resolution was 3 μm for the band at a wavelength of ca. 3 μm. The spatial resolution was also assessed with and without the added lens, in normal and high-magnification modes using a USAF target. Spectroscopic images of cells in transmission mode using two lenses are also presented, which are necessary for correcting chromatic aberration and refraction in both the condenser and objective. The use of lenses is shown to be necessary for obtaining high-quality spectroscopic images of cells in transmission mode and proves the applicability of the pseudo hemisphere approach for this and other microfluidic systems.

Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR FT-IR) Mapping Coupled with Multivariate Curve Resolution (MCR) for Studying the Miscibility of Chlorobutyl Rubber/Polyamide-12 Blends

A series of chlorobutyl rubber/polyamide-12 (CIIR/PA-12) blends compatibilized by different amounts of maleic anhydride (MAH) grafted polypropylene (PP-g-MAH) were investigated by attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) mapping. Multivariate curve resolution (MCR) was used to process the FT-IR images. Both the spectra of pure components in the blends and their concentration distributions in a micro-region were acquired. Our results demonstrated that the blend with 15 parts per hundred rubber PP-g-MAH showed the best miscibility. An amide interphase and an imide interphase were inferred by analyzing the spectra of MCR component 3 of the blends with and without PP-g-MAH, respectively. Correspondingly, two different compatibilizing mechanisms were proposed for these blends.

Poly(3-hydroxybutyrate)/ZnO bionanocomposites with improved mechanical, barrier and antibacterial properties

Poly(3-hydroxybutyrate) (PHB)-based bionanocomposites incorporating different contents of ZnO nanoparticles were prepared via solution casting technique. The nanoparticles were dispersed within the biopolymer without the need for surfactants or coupling agents. The morphology, thermal, mechanical, barrier, migration and antibacterial properties of the nanocomposites were investigated. The nanoparticles acted as nucleating agents, increasing the crystallization temperature and the degree of crystallinity of the matrix, and as mass transport barriers, hindering the diffusion of volatiles generated during the decomposition process, leading to higher thermal stability. The Young's modulus, tensile and impact strength of the biopolymer were enhanced by up to 43%, 32% and 26%, respectively, due to the strong matrix-nanofiller interfacial adhesion attained via hydrogen bonding interactions, as revealed by the FT-IR spectra. Moreover, the nanocomposites exhibited reduced water uptake and superior gas and vapour barrier properties compared to neat PHB. They also showed antibacterial activity against both Gram-positive and Gram-negative bacteria, which was progressively improved upon increasing ZnO concentration. The migration levels of PHB/ZnO composites in both non-polar and polar simulants decreased with increasing nanoparticle content, and were well below the current legislative limits for food packaging materials. These biodegradable nanocomposites show great potential as an alternative to synthetic plastic packaging materials especially for use in food and beverage containers and disposable applications.

Structural determination of protein-based polymer blends with a promising tool: combination of FTIR and STXM spectroscopic imaging

The combination of FTIR and STXM imaging provides complimentary information that enables a greater understanding of protein-based polymer blends. They can monitor the phase separation behavior of the blends, and show the composition and protein conformation difference in two phases.

Tuning the degradation profiles of poly(L-lactide)-based materials through miscibility

The effective use of biodegradable polymers relies on the ability to control the onset of and time needed for degradation. Preferably, the material properties should be retained throughout the intended time frame, and the material should degrade in a rapid and controlled manner afterward. The degradation profiles of polyester materials were controlled through their miscibility. Systems composed of PLLA blended with poly[(R,S)-3-hydroxybutyrate] (a-PHB) and polypropylene adipate (PPA) with various molar masses were prepared through extrusion. Three different systems were used: miscible (PLLA/a-PHB5 and PLLA/a-PHB20), partially miscible (PLLA/PPA5/comp and PLLA/PPA20/comp), and immiscible (PLLA/PPA5 and PLLA/PPA20) blends. These blends and their respective homopolymers were hydrolytically degraded in water at 37 °C for up to 1 year. The blends exhibited entirely different degradation profiles but showed no diversity between the total degradation times of the materials. PLLA presented a two-stage degradation profile with a rapid decrease in molar mass during the early stages of degradation, similar to the profile of PLLA/a-PHB5. PLLA/a-PHB20 presented a single, constant linear degradation profile. PLLA/PPA5 and PLLA/PPA20 showed completely opposing degradation profiles relative to PLLA, exhibiting a slow initial phase and a rapid decrease after a prolonged degradation time. PLLA/PPA5/comp and PLLA/PPA20/comp had degradation profiles between those of the miscible and the immiscible blends. The molar masses of the materials were approximately the same after 1 year of degradation despite their different profiles. The blend composition and topographical images captured at the last degradation time point demonstrate that the blending component was not leached out during the period of study. The hydrolytic stability of degradable polyester materials can be tailored to obtain different and predetermined degradation profiles for future applications.

Synthesis, characterization, biodegradability and biocompatibility of a temperature-sensitive PBLA-PEG-PBLA hydrogel as protein delivery system with low critical gelation concentration

Temperature-sensitive hydrogels were designed using a series of A-B-A triblock copolymers consisting of poly (ethylene glycol) (PEG) with different molecular weights as the hydrophilic block B and poly (β-butyrolactone-co-lactic acid)(PBLA) with varying block lengths and composition as the hydrophobic block A. The triblock copolymers were synthesized by ring-opening polymerization (ROP) of β-BL and LA in bulk using PEG as an initiator and Sn(Oct)2 as the catalyst. Their chemical structure and molecular characteristics were determined by NMR, GPC and DSC, and the relationship between structure and phase behaviors in aqueous solutions was investigated as well. It was found that the phase behaviors in aqueous solutions including critical micelle concentration (CMC), sol-gel-sedimentation phase transition temperature, gel window width and critical gelation concentration (CGC) are largely dependent on the molecular weight and block length ratio of PEG/PBLA. Most importantly, they show a very low CGC ranging from 4 to 8 wt% because of the introduction of β-BL. Furthermore, the biodegradability and biocompatibility of the hydrogels were evaluated. Finally, lysozyme as a model protein was used to evaluate the ability to deliver protein drugs in a sustained release manner and biologically active form. All results demonstrated that the temperature-sensitive in situ forming hydrogel has a promising potential as sustained delivery system for protein drugs.

Temperature-dependent Fourier transform infrared spectroscopy and Raman mapping spectroscopy of phase-separation in a poly(3-hydroxybutyrate)-poly(L-lactic acid) blend

Variable-temperature Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopic mapping measurements were applied to study the phase separation of a poly(3-hydroxybutyrate) (PHB)-poly(L-lactic acid) (PLA) (50 : 50 wt.%) polymer-blend film as a function of temperature between 25 and 175 °C. Because of the better band separation compared with the fundamental absorptions, the first overtones of the ν(C=O) bands of PHB and PLA were used to evaluate the temperature-dependent FT-IR images as PLA-PHB and PHB-PLA band-ratio contour plots, respectively. From the visualization of the band-ratio FT-IR images, it could be derived that even beyond the melting point of PLA (145 °C), the lateral position and the geometry of the PHB-rich and PLA-rich phases were retained up to 165 °C. Furthermore, the FT-IR images derived during and after the melting of PHB (174 °C) provided an interesting insight into the homogenization process of the polymer melt. By exploiting its higher lateral resolution, valuable additional information became available from the Raman mapping measurements. Based on the Raman data, the scenario of phase-separated PHB-rich and PLA-rich domains of about 50 μm size, based on the FT-IR imaging measurements, had to be revised. Instead, the originally interpreted PHB-rich and PLA-rich domains are actually clusters of much smaller grains. Additionally, the Raman images measured in the same temperature interval revealed that the clusters of small PHB-rich grain structures aggregated as a function of temperature increase. These investigations prove that FT-IR and Raman imaging in combination with variable-temperature measurements can provide new (and so far unavailable) insights into structural phenomena of phase-separated polymer blends.

Generation of poly-β-hydroxybutyrate from externally provided acetate in rice root

During the investigation of the metabolism of ¹⁴C-acetate or ¹⁴C-succinate in rice seedlings, an unknown organic acid (X) with a high specific radioactivity was detected in 10,000 × g 30 min precipitate-fraction of rice roots. The X was hardly extracted by 0.1 N-H₂SO₄ boiling, but was extracted by 0.5 N-KOH boiling. The X was co-chromatographed with several known organic acids, and the radioactive peak of the X matched β-hydroxybutyric acid (β-hydroxybutyrate). The radioactive X and β-hydroxybutyrate were then heated with concentrated H₂SO₄. The radioactivity and the titration value were completely converted to crotonic acid. Thus, it was concluded that the X was β-hydroxybutyrate, and the original form of this acid was presumed to be poly-β-hydroxybutyrate (PHB). Then rice root incubated with 2-¹⁴C-acetate was extracted with hot-ethanol, ethanol/ether, and hot-chloroform. Approximately 10% of the radioactivity absorbed was detected in the chloroform fraction. The chloroform fraction was co-precipitated with authentic PHB by the addition of acetone/ether, and almost all the radioactivity was co-precipitated with the PHB. The radioactive co-precipitate was then heated with 0.5 N-NaOH, and chromatographed. The radioactivity of β-hydroxybutyrate plus crotonic acid almost matched that of the co-precipitate before alkaline-hydrolysis. Hence the radioactive co-precipitate was confirmed to be PHB. In wheat and radish seedlings, 2-¹⁴C-acetate was also assimilated into PHB. It is concluded that externally provided acetate was rapidly converted to PHB in higher plants.

Phase morphology, physical properties, and biodegradation behavior of novel PLA/PHBHHx blends

In this study, two biodegradable polyesters [i.e., polylactic acid (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx)] with complementarity in terms of mechanical performance have been combined, and a series of blends with a broad range of compositions has been prepared by thermal compounding. The evolution of phase morphologies with the variation of compositions has been characterized by using Fourier transform infrared spectroscopic imaging together with scanning electron microscope analyses. Thermal, mechanical, and biodegradation properties of the PLA/PHBHHx blends were systematically investigated. Mechanical properties were further analyzed by using theoretical models and correlated with the results of the morphology/structure and compatibility of the blends. Results indicate that PLA/PHBHHx blends are immiscible but can be compatible to some extent at certain compositions (e.g., PLA/PHBHHx (w/w) = 80/20 and 20/80). The physical properties of the blend could be fine tuned by adjusting the blend composition.

Manipulation of Polyhydroxybutyrate Properties through Blending with Ethyl-Cellulose for a Composite Biomaterial

Polyhydroxybutyrate (PHB) is widely used as a biomaterial in medical and tissue-engineering applications, a relatively high crystallinity limits its application. Blending PHB with ethyl-cellulose (EtC) was readily achieved to reduce PHB crystallinity and promote its degradation under physiological conditions without undue influence on biocompatibility. Material strength of composite films remained unchanged at 6.5±0.6 MPa with 40% (w/w) EtC loadings. Phase separation between the two biopolymers was determined with PHB crystallinity decreasing from 63% to 47% for films with the same loading. This reduction in crystallinity supported an increase in the degradation rates of composite films from 0.39 to 0.81% wk−1for PHB and its composite, respectively. No significant change in morphology and proliferation of olfactory ensheathing cells were observed with the composites despite significant increases in average surface roughness (Ra) of the films from 2.90 to 3.65 μm for PHB and blends with 80% (w/w) EtC, respectively.