Thermoplastic Polyester Research Articles

Rosin natural terpenes as processing aid for polyhydroxyalkanoate: Thermal, mechanical, and viscoelastic properties

AbstractRosin natural terpene (Dertoline) is compounded with a bacterial thermoplastic polyesters polyhydroxyalkanoate (PHA), specifically here poly(3‐hydroxybutyrate) (PHB), a biodegradable and biocompatible polymer. The compatibility of the blend is examined with differential scanning calorimetry and thermal gravimetry analysis. In the range of concentration of Dertoline, from 5 to 15 wt%, a cold crystallization peak first shifts to slightly higher then lower temperature. Dynamical mechanical analysis and tensile tests confirm that the addition of Dertoline slightly decreases the elastic modulus. The degree of crystallinity again increases then decreases with the content of Dertoline. Polarized light microscopy reveals smaller diameter spherulites for PHB/Dertoline blends and their presence is discussed in relation to tensile tests. Overall, the addition of Dertoline has limited effects on mechanical properties of the blends: the stress at break and the strain at break. In addition, oscillatory rheology at different temperatures provides the activation energies and the parameters of a generalized Maxwell model. The temperature dependence of the rheological properties follows an Arrhenius form. Finally, transient step viscosity measurements are used in order to quantify the PHB thermal degradation.

Fabrication strategy for long‐chain branched polypropylene foams with high resilience and compressive strength

AbstractA flexible and controllable is proposed for fabricating long‐chain branched polypropylene (LCBPP) foams with high resilience and strength. LCBPP was blended with thermoplastic polyester elastomer (TPEE) using polyethylene octene elastomer grafted glycidyl methacrylate (POE‐g‐GMA) as a compatibilizer at different mass ratios, and the blends were then used to prepare foams at different temperatures by the supercritical CO2 batch foaming method. The foams were then tested for their compressive permanent strain and compressive strength. The results showed that introducing TPEE and POE‐g‐GMA increased the resilience. In particular, the permanent strain of the LCBPP/TPEE/POE‐g‐GMA foam at a ratio of 90/10/7 decreased from an initial 14.5% for the original LCBPP foam to 5% after five compression cycles. However, the compressive strength decreased from 65.59 to 39.82 kPa. Therefore, the foam density (ρ) and cell size (d) were adjusted to balance the resilience and strength. Increasing ρ/d from 0.32 to 3.10 increased the compressive strength significantly from 39.82 to 91.67 kPa while the permanent strain only increased 3.5%. Thus, the proposed strategy realized LCBPP foams with high resilience and compressive strength.

Distinct degradation behaviors of semi-crystalline poly (4-hydroxybutyrate) containing a nucleating agent under enzymatic or alkaline conditions

Poly(4-hydroxybutyrate) (P4HB) is an absorbable thermoplastic polyester with excellent mechanical properties, good biodegradability and biocompatibility, and has great application prospects in the biomedical field. Therefore, it is of great significance to adjust the degradation rate of P4HB to meet the needs of different application scenarios. In this work, the effects of multimethyl-benzilidene sorbitol (TM6) on the crystallization and degradation behaviors of P4HB were studied. The differential scanning calorimetry, polarized optical microscopy and atomic force microscopy results indicated that TM6 increased the crystallization rate of P4HB as heterogeneous nuclei. The results of weight loss and gel permeation chromatography measurements indicated that both enzymatic and alkaline degradation proceeded via a surface erosion, while the effects of TM6 on the respective degradation rates were quite different. When TM6 content reached 0.5 wt%, the enzymatic degradation rate of P4HB was significantly reduced, and the degraded surface showed a network structure, indicating that TM6-induced crystals were difficult to be degraded, which may be attributed to the high local crystallinity around linear TM6 and/or the different spatial arrangements of TM6-induced crystals. However, the alkaline degradation rate of P4HB was slightly increased because the introduction of TM6 decreased the overall crystallinity. The scanning electron microscope results of P4HB composites after degradation suggested that the enzymatic degradation had higher selectivity to the local physical structure. Based on the degradation results, microspheres with holes or loose nanofibrous structures on the surface were prepared. The cell culture results on the microspheres indicated that nanofibrous structure were more conducive to the adhesion and growth of MG-63 cells. This method for regulating the surface structure of scaffolds is simple and easy to implement, so it has great application potential in the field of tissue engineering.

Sol-Gel Assisted Immobilization of Alizarin Red S on Polyester Fabrics for Developing Stimuli-Responsive Wearable Sensors

In the field of stimuli-responsive materials, introducing a pH-sensitive dyestuff onto textile fabrics is a promising approach for the development of wearable sensors. In this paper, the alizarin red S dyestuff bonded with a sol-gel precursor, namely trimethoxy-[3-(oxiran-2-ylmethoxy)propyl]silane, was used to functionalize polyethylene terephthalate fabrics, a semi-crystalline thermoplastic polyester largely used in the healthcare sector mainly due to its advantages, including mechanical strength, biocompatibility and resistance against abrasion and chemicals. The obtained hybrid halochromic silane-based coating on polyester fabrics was investigated with several chemical characterization techniques. Fourier transform infrared spectroscopy and X-ray Photoelectron Spectroscopy confirmed the immobilization of the dyestuff-based silane matrix onto polyethylene terephthalate samples through self-condensation of hydrolyzed silanols under the curing process. The reversibility and repeatability of pH-sensing properties of treated polyester fabrics in the pH range 2.0–8.0 were confirmed with diffuse reflectance and CIELAB color space characterizations. Polyester fabric functionalized with halochromic silane-based coating shows the durability of halochromic properties conversely to fabric treated with plain alizarin red S, thus highlighting the potentiality of the sol-gel approach in developing durable halochromic coating on synthetic substrates. The developed wearable pH-meter device could find applications as a non-invasive pH sensor for wellness and healthcare fields.

Use of Polyesters in Fused Deposition Modeling for Biomedical Applications

In recent years, 3D printing techniques experience a growing interest in several sectors, including the biomedical one. Their main advantage resides in the possibility to obtain complex and personalized structures in a cost-effective way impossible to achieve with traditional production methods. This is especially true for fused deposition modeling (FDM), one of the most diffused 3D printing methods. The easy customization of the final products' geometry, composition, and physicochemical properties is particularly interesting for the increasingly personalized approach adopted in modern medicine. Thermoplastic polymers are the preferred choice for FDM applications, and a wide selection of biocompatible and biodegradable materials is available to this aim. Moreover, these polymers can also be easily modified before and after printing to better suit the body environment and the mechanical properties of biological tissues. This review focuses on the use of thermoplastic aliphatic polyesters for FDM applications in the biomedical field. In detail, the use of poly(ε-caprolactone), poly(lactic acid), poly(lactic-co-glycolic acid), poly(hydroxyalkanoate)s, thermoplastic poly(ester urethane)s, and their blends is thoroughly surveyed, with particular attention to their main features, applicability, and workability. The state-of-the-art is presented and current challenges in integrating the additive manufacturing technology in the medical practice are discussed.

X-ray Ptychographic Imaging and Spectroscopic Studies of Plasma-Treated Plastic Films.

Polyethylene terephthalate (PET) is a thermoplastic polyester with numerous applications in industry. However, it requires surface modification on an industrial scale for printing and coating processes and plasma treatment is one of the most commonly used techniques to increase the hydrophilicity of the PET films. Systematic improvement of the surface modification by adaption of the plasma process can be aided by a comprehensive understanding of the surface morphology and chemistry. However, imaging large surface areas (tens of microns) with a resolution that allows understanding the surface quality and modification is challenging. As a proof-of-principle, plasma-treated PET films were used to demonstrate the capabilities of X-ray ptychography, currently under development at the soft X-ray free-electron laser FLASH at DESY, for imaging macroscopic samples. In combination with scanning electron microscopy (SEM), this new technique was used to study the effects of different plasma treatment processes on PET plastic films. The studies on the surface morphology were complemented by investigations of the surface chemistry using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). While both imaging techniques consistently showed an increase in roughness and change in morphology of the PET films after plasma treatment, X-ray ptychography can provide additional information on the three-dimensional morphology of the surface. At the same time, the chemical analysis shows an increase in the oxygen content and polarity of the surface without significant damage to the polymer, which is important for printing and coating processes.

Compressive Properties of Polyurethane Fiber Mattress Filling Material

There is an inevitable trend toward exploring new, environmentally friendly fibers that can be used as raw material for mattresses with moderate hardness and air-permeable characteristics. Ethylene-propylene side by side (ES), high-shrinkage fibers, and thermoplastic polyester elastomer (TPEE) chips were introduced into polyethylene glycol terephthalate (PET)/polybutylene terephthalate (PBT) chip by melt blending to modify PET/PBT fiber. The modified PET/PBT (hereinafter referred to as PLON) is more suitable for mattress filling material than PET/PBT. To explore the compressive properties of PLON cushion made of PLON fiber and expand the scope of the PLON cushion’s application, a layered hardness test, hardness classification test and variance analysis were used to comprehensively evaluate the surface hardness, core hardness, bottom hardness and hardness classification of the mattress made of PLON cushion. The conclusions are: (1) The materials of the support layer have a significant effect on the hardness grade S. The hardness of the mattress with PLON as the support layer is between the spring and the coir; (2) when PLON is used as the material of the support layer, it possesses higher supporting force than coir and the characteristics of light weight and high resilience, which coir does not have; it is also softer than a spring mattress. As cushion material, it provides higher support for mattresses than foam. Practical applications, densities and structure were clarified through the above research, with implications for broader applications for PLON blocks in mattress products.

Anti-shrinkage, high-elastic, and strong thermoplastic polyester elastomer foams fabricated by microcellular foaming with CO2 & N2 as blowing agents

Thermoplastic polyester elastomer (TPEE) is a high-performance polymer with high tear strength and excellent abrasion resistance, and microcellular TPEE foams exhibit low density and special mechanical properties. Nevertheless, shrinkage behavior of the TPEE foam is still a critical challenge which greatly limits its industrial application, and further, the shrinkage mechanism is rarely figured out. Herein, a novel strategy of implementing mixed CO2 & N2 as blowing agents in microcellular foaming was developed to stabilize cell structure. Thanks to the modest permeability of mixed blowing agents, TPEE foams with high stable expansion ratio of higher than 17-fold and recovery ratio of up to 77 % were fabricated, and it found that the ratio of mixed blowing agents could modulate the shrinkage behavior of TPEE foams. Moreover, the correlation between the mechanical properties and TPEE foams with different shrinkage behaviors was investigated. For TPEE foams with similar stable expansion ratios, decreasing the shrinkage helped to increase the maximum compressive stress by 100 % and to reduce the energy loss coefficient by 43 %. Overall, the developed microcellular foaming prepared with the mixed CO2 & N2 as blowing agents shows great promise in fabricating advanced elastomer foams with high expansion ratio, stable cell morphology and outstanding mechanical properties.

A Step Forward in Thermoplastic Polyesters: Understanding the Crystallization and Melting of Biobased Poly(ethylene 2,5-furandicarboxylate) (PEF)

A Step Forward in Thermoplastic Polyesters: Understanding the Crystallization and Melting of Biobased Poly(ethylene 2,5-furandicarboxylate) (PEF)

Flame-retardation of thermoplastic polyesters via cyclotetramerization from phthalonitrile to phthalocyanine: Pyrolysis processes and fire behaviour

Flame retardancy is a way to enhance the fire safety performance of polymers, which can slow down the flame spread and reduce the severity of fire events. Phthalocyanines (Pcs) skeletons have unleashed high flame-retardant efficiency in thermosetting resins. However, limited by the high stability and bulky structure of Pcs, how to make this classic macrocyclic structure play its flame retardant advantages in thermoplastic polymers is still a significant challenge. We synthesized flame-retardant copolyesters (CxPET) via chemically incorporating the phenoxyphthalonitrile structures into the polymer chains of poly(ethylene terephthalate) (PET) by melt polymerization. PY-GC–MS tests at 400, 500, and 700 °C are performed to detailedly investigate the pyrolysis processes. The TGA, LOI, and UL-94 tests are carried out to reveal the burning behavior. The LOI, vertical UL-94, and cone calorimeter tests, are used to characterize the flame-retardant properties and the fire behavior. The copolyesters, containing phenoxyphthalonitrile structures, exhibit good flame retardance (LOI 30.0, UL-94V-0 level with no dripping producing). The peak heat release rate (337 ± 32 kW m−2) and TSR (1377 ± 74 m2 m−2) are also reduced by 55.4% and 20.2%, compared with PET. Combining the pyrolysis processes and fire behavior results, the phthalonitrile structures can be quickly transformed into phthalocyanine structures at high temperatures. Further, the formed phthalocyanines play a flame-retardant role via promoting the charring of copolyesters. Therefore, this work supplies an available way to play the flame retardant advantages of phthalocyanine macrocyclic in thermoplastic polymers, and provides key guidance for the design of safer polymers.

Generation of Tough, Stiff Polylactide Nanocomposites through the In Situ Nanofibrillation of Thermoplastic Elastomer.

Polylactide (PLA) resins are among the most desirable biopolymers due to their biobased and compostable nature, excellent stiffness, and tensile strength. However, the widespread application of PLA has long been hindered by its inherent brittleness. While multiple routes have been successfully developed for the toughening of PLA, this toughening has always come at the cost of compromising the stiffness and strength of the matrix. In this work, we report a robust and scalable method for the development of PLA nanocomposites with an unprecedented combination of stiffness and toughness. Using the in situ nanofibrillation technique, we generated PLA composites containing nanofibrils of thermoplastic polyester elastomer (TPEE). Due to the high aspect ratio of these nanofibrils, they form physically percolated networks at low weight fractions (∼2.8 wt %) which dramatically change the mechanical behavior of the material. We found that, upon network formation, the material transitions from brittle to ductile behavior, dramatically increasing its toughness with only a marginal decrease in Young's modulus. We investigate the peculiar rheological behavior and crystallization kinetics of these blends, and propose an extension of the critical ligament thickness mechanism, wherein intrinsic toughening arises at the fiber-matrix interface in the presence of entangled elastomer networks.

Poly (Lactic Acid) Nanoparticles: A Promising Hope to Overcome the Cancers

Nanoparticles are used mainly for the transmission of the therapeutic molecules (like drugs, proteins, or DNA) to the organ/tissue of human body. Polymeric nanoparticles are mostly applied for therapeutic effectiveness in cancer therapy. The micro environment of tumor tissues in vessels can assist nanoparticles in achieving their anticipated accumulation. Poly (lactic acid)(PLA) is a novel green polymer with natural sources (like sweet potato and sugar cane). PLA is a linear aliphatic which has great sustainability, renewability and compostability. PLA has popper mechanical, thermal and barrier properties. This biomaterial is thermoplastic polyester with biocompatibility, non-toxicity and biodegradability. Various forms of PLA nanoparticles are synthetized for biomedical applications like cancer treatments and wound healing process. This review article introduces the various structures of polylactic acid nanoparticles used to deliver anticancer drugs. Furthermore, the investigational approaches that are considered for using PLA nanoparticles in treatment of different types of cancers will be reported briefly.

Electron Beam-Mediated Cross-Linking of Blown Film-Extruded Biodegradable PGA/PBAT Blends toward High Toughness and Low Oxygen Permeation

Due to its high crystallinity, tailored compostability, and superior barrier performance, poly(glycolic acid) (PGA) has great potential as a substitute for current single-use plastics used in food packaging applications and with a lower carbon footprint. However, its susceptibility to hydrolysis and mechanical brittleness hinders its direct suitability in packaging. In this work, we circumvent this limitation by first blending PGA with a thermoplastic polyester, poly(butylene adipate-co-terephthalate) (PBAT), and a glycidyl cross-linker via industrial-scale twin-screw extrusion and then converting to a film by blown film extrusion. The surface of the films was then chemically cross-linked using electron beam treatment (EBT) to impart excellent barrier properties. Here, the electron beam plays a dual role. Firstly, it cross-links the surface of the films and improves the oxygen and moisture barrier performance, both improved due to blending with PBAT. Second, it does not compromise the toughness or extension at break of the polymer blend, both desirable for flexible packaging applications. A dosage of 250 kGy EBT resulted in the film having an oxygen barrier permeation of 57.0–59.8 cm3 mm m–2 24 h–1 atm–1 and a water vapor permeation of 26.8 g m–2 24 h–1 while maintaining a high toughness of 75 MPa. At dosages higher than 300 kGy, inhomogeneities formed on the surface of the films and some degradation in the mechanical properties of the films is observed. This work highlights the possibility of deriving superior biopolymer barrier performance while retaining the mechanical properties required for food packaging using a combination of blending and electron beam treatment, both scalable processes.

Post-Synthetic Enzymatic and Chemical Modifications for Novel Sustainable Polyesters

Because of their biodegradability, compostability, compatibility and flexible structures, biodegradable polymers such as polyhydroxyalkanoates (PHA) are an important class of biopolymers with various industrial and biological uses. PHAs are thermoplastic polyesters with a limited processability due to their low heat resistance. Furthermore, due to their high crystallinity, some PHAs are stiff and brittle. These features result sometimes in very poor mechanical characteristics with low extension at break values which limit the application range of some natural PHAs. Several in vivo approaches for PHA copolymer modifications range from polymer production to enhance PHA-based material performance after synthesis. The methods for enzymatic and chemical polymer modifications are aiming at modifying the structures of the polyesters and thereby their characteristics while retaining the biodegradability. This survey illustrates the efficient use of enzymes and chemicals in post-synthetic PHA modifications, offering insights on these green techniques for modifying and improving polymer performance. Important studies in this sector will be reviewed, as well as chances and obstacles for their stability and hyper-production.

Setting the Optimal Laser Power for Sustainable Powder Bed Fusion Processing of Elastomeric Polyesters: A Combined Experimental and Theoretical Study.

Additive manufacturing (AM) of polymeric materials offers many benefits, from rapid prototyping to the production of end-use material parts. Powder bed fusion (PBF), more specifically selective laser sintering (SLS), is a very promising AM technology. However, up until now, most SLS research has been directed toward polyamide powders. In addition, only basic models have been put forward that are less directed to the identification of the most suited operating conditions in a sustainable production context. In the present combined experimental and theoretical study, the impacts of several SLS processing parameters (e.g., laser power, part bed temperature, and layer thickness) are investigated for a thermoplastic elastomer polyester by means of colorimetric, morphological, physical, and mechanical analysis of the printed parts. It is shown that an optimal SLS processing window exists in which the printed polyester material presents a higher density and better mechanical properties as well as a low yellowing index, specifically upon using a laser power of 17–20 W. It is further highlighted that the current models are not accurate enough at predicting the laser power at which thermal degradation occurs. Updated and more fundamental equations are therefore proposed, and guidelines are formulated to better assess the laser power for degradation and the maximal temperature achieved during sintering. This is performed by employing the reflection and absorbance of the laser light and taking into account the particle size distribution of the powder material.

Structure-Property Relationship in Melt-Spun Poly(hydroxybutyrate-co-3-hexanoate) Monofilaments.

Poly(hydroxybutyrate-co-3-hexanoate) (PHBH) is a biodegradable thermoplastic polyester with the potential to be used in textile and medical applications. We have aimed at developing an upscalable melt-spinning method to produce fine biodegradable PHBH filaments without the use of an ice water bath or offline drawing techniques. We have evaluated the effect of different polymer grades (mol% 3-hydroxy hexanoate, molecular weight etc.) and production parameters on the tensile properties of melt-spun filaments. PHBH monofilaments (diameter < 130 µm) have been successfully melt-spun and online drawn from three different polymer grades. We report thermal and rheological properties of the polymer grades as well as morphological, thermal, mechanical, and structural properties of the melt-spun filaments thereof. Tensile strengths up to 291 MPa have been achieved. Differences in tensile performance have been correlated to structural differences with wide-angle X-ray diffraction and small-angle X-ray scattering. The measurements obtained have revealed that a synergetic interaction of a highly oriented non-crystalline mesophase with highly oriented α-crystals leads to increased tensile strength. Additionally, the effect of aging on the structure and tensile performance has been investigated.

Design optimization of PLA lattice in 3D printing

Polylactic acid (PLA), a thermoplastic polyester is an eco-friendly, biodegradable material that is used to develop strong Lattice components at low temperatures using fused deposition modelling (FDM) 3D Printing. PLA Lattices are used for diverse applications as medical implants, automotive, aviation, shape resuming memory parts, smart fabric, bio-printing, sensing instrument and many more. Parameters as volume fragment, unit cell shapes and size can be brought into play to create a competent PLA lattice depending upon the type of application and desired property. Octet truss, BCC, and CCP are commonly used unit cells, and usually fail due to stress concentration at the joining edges of trusses. Amongst these, the octet shaped truss lattice structure can withstand greater load and is suggested for load-bearing applications but is difficult to develop. In present work an effort is made to develop a strong CCP lattice structure by optimizing design factors as, unit cell and lattice size, layer height, filament print temperature and speed, infill density and pattern, support types, build orientation and temperature, layer height; and other influencing parameters to increase strength of the 3D printed Lattice part. It is observed that surrounding environment as humidity and temperature, critically affects the strength and surface finish of the fabricated PLA lattice structure.

3D printing of single-walled objects

Material deposition additive manufacturing, commonly known as fused deposition modeling (FDM) or 3D printing, is gradually becoming popular for engineering applications ranging from biomedical to construction. In many of these applications, the manufactured objects need to be hollow, or with thin walls. For example, personalized medicines may require 3d printing of thin-walled capsules, and 3D printed housing solutions require single wall of construction structures. Keeping such applications in mind, this paper studies the single-wall extrusion behavior of polylactic acid, a thermoplastic polyester commonly used in 3D printing. Different extrusion parameters, namely, printing temperature, printing speed, layer thickness, extrusion rate etc. have been explored, and their examined their effects on the extrusion properties. The thickness and the uniformity of extrusion were considered as the output parameters. It was observed that the printing temperature has a very significant effect on the achievable flow rate of the extruded material, as higher flow rate requires higher thermal input from the nozzle wall. It is possible to increase flow rate by increasing nozzle temperature, but that may adversely affect the uniformity of the extrusion.

Egg Yolk Oil as a Plasticizer for Polylactic Acid Films.

Polylactic acid (PLA) is known to be one of the most extensively used biodegradable thermoplastic polyesters, with the potential to replace conventional petroleum-based packaging materials; however, the low flexibility of films prepared using PLA has limited the applications of this biopolymer. In this study, in order to improve the mechanical properties of PLA films and to provide them with antioxidant properties, egg yolk oil was used as a biobased plasticizer. For this purpose, PLA films with increasing concentrations of egg yolk oil were prepared and the effects of this oil on the light transmission, transparency, colour, water vapour permeability, solubility, antioxidant activity and mechanical properties of the films were characterized. In addition, electron microscopy of the structure of the transverse section of the films was also performed. Results showed that the formulations with higher concentrations of egg yolk oil increased the films’ elasticity, and their light barrier and antioxidant properties. Finally, in order to test the films as a packaging material for food applications, extra virgin olive oil and resveratrol, both photosensitive compounds, were packed and exposed to ambient light. Overall, the results show the potential of egg yolk oil as an environmentally friendly plasticizer that can improve the flexibility of PLA films and provide them with additional photoprotective properties.

A local green composite study: the effect of edible oil on the morphological and mechanical properties of PBS/bentonite composite

Abstract Composites of a biodegradable thermoplastic aliphatic polyester, polybutylene succinate (PBS), with bentonite were investigated for morphological and mechanical properties. The bentonite was modified with soybean oil (SBO) and lard oil (LO) (2:98 clay:oil % by weight) by mechanical stirring and ultrasonication. The PBS/modified bentonite composite was prepared by using an internal mixer and processed by compression molding. Under bentonite modification conditions, XRD and SEM showed that the bentonite layers were broken into small layers, and the d-spacing between the layers was increased by edible oil molecules. A small plate like structure of modified bentonite composite was observed by SEM micrograph, which revealed short and long layer silicate structure non-directionally throughout the matrix phase. The mechanical properties of PBS were reinforced by this structure. The tensile modulus and elongation at break seem to depend on its directional bentonite. Interestingly, considerable improvement in impact strength was observed at over 2 wt% of clay. The impact strengths of PBS, PBS/modified BTN with SBO composite, and PBS/modified BTN with LO composite were increased from 1 to 1.5 and 2 kJ/m2, respectively. Comparatively, using LO modified bentonite had a better performance for increased interlayer and resulted in higher impact strength of the composite than that of SBO composite. The results demonstrated that PBS/modified bentonite using edible oil could be a potential alternative low cost, eco-friendly material with superior impact properties useful for further applications.