Study on the effect of dispersion phase morphology on porous structure of poly (lactic acid)/poly (ethylene terephthalate glycol-modified) blending foams

Super toughened blends of poly(lactic acid) and poly(butylene adipate-co-terephthalate) injection-molded foams via enhancing interfacial compatibility and cellular structure

Biodegradable poly(lactic acid) (PLA) foams have drawn increasing attention due to environmental challenges and petroleum crisis. However, it still remains a challenge to prepare PLA foams with fine cellular structures and high impact property, which significantly hinders its widespread application. Herein, phase interface-enhanced PLA/ poly(butylene adipate-co-terephthalate) (PBAT) blend foam, modified by a reactive compatibilizer through a simple reactive extrusion, was produced via a core-back foam injection molding technique. The obtained PLA blend foams displayed an impact strength as high as 49.1 kJ/m², which was 9.3 and 6.4 times that of the unmodified PLA/PBAT blend and its corresponding foam, respectively. It proved that the interfacial adhesion and cell size both strongly affected the impact strength of injection-molded PLA/PBAT foams, and two major conclusions were proposed. First, enhancing interfacial adhesion could cause a brittle-tough transition of PLA/PBAT foams. Additionally, for foams with high interfacial adhesion, small cell size (<12 μm) was more favorable for the stretching of cells and extension of the whitened region in comparison with big cell size (cell size >60 μm), leading to the drastic toughening of PLA blends. This study provides a feasible, industrially scalable and practical strategy to prepare super toughened and fully biodegradable PLA materials.

In Situ Nanofibrillar Polypropylene-Based Composite Microcellular Foams with Enhanced Mechanical and Flame-Retardant Performances

With the increasing demand for plastic components, the development of lightweight, high strength and functionalized polypropylene (PP) from a cost-effective and environmentally friendly process is critical for resource conservation. In situ fibrillation (INF) and supercritical CO2 (scCO2) foaming technology were combined in this work to fabricate PP foams. Polyethylene terephthalate (PET) and poly(diaryloxyphosphazene)(PDPP) particles were applied to fabricate in situ fibrillated PP/PET/PDPP composite foams with enhanced mechanical properties and favorable flame-retardant performance. The existence of PET nanofibrils with a diameter of 270 nm were uniformly dispersed in PP matrix and served multiple roles by tuning melt viscoelasticity for improving microcellular foaming behavior, enhancing crystallization of PP matrix and contributing to improving the uniformity of PDPP’s dispersion in INF composite. Compared to pure PP foam, PP/PET(F)/PDPP foam exhibited refined cellular structures, thus the cell size of PP/PET(F)/PDPP foam was decreased from 69 to 23 μm, and the cell density increased from 5.4 × 106 to 1.8 × 108 cells/cm3. Furthermore, PP/PET(F)/PDPP foam showed remarkable mechanical properties, including a 975% increase in compressive stress, which was attributed to the physical entangled PET nanofibrils and refined cellular structure. Moreover, the presence of PET nanofibrils also improved the intrinsic flame-retardant nature of PDPP. The synergistical effect of the PET nanofibrillar network and low loading of PDPP additives inhibited the combustion process. These gathered advantages of PP/PET(F)/PDPP foam make it promising for lightweight, strong, and fire-retardant polymeric foams.

Load Distribution on PET-G 3D Prints of Honeycomb Cellular Structures under Compression Load

Energy resulting from an impact is manifested through unwanted damage to objects or persons. New materials made of cellular structures have enhanced energy absorption (EA) capabilities. The hexagonal honeycomb is widely known for its space-filling capacity, structural stability, and high EA potential. Additive manufacturing (AM) technologies have been effectively useful in a vast range of applications. The evolution of these technologies has been studied continuously, with a focus on improving the mechanical and structural characteristics of three-dimensional (3D)-printed models to create complex quality parts that satisfy design and mechanical requirements. In this study, 3D honeycomb structures of novel material polyethylene terephthalate glycol (PET-G) were fabricated by the fused deposition modeling (FDM) method with different infill density values (30%, 70%, and 100%) and printing orientations (edge, flat, and upright). The effectiveness for EA of the design and the effect of the process parameters of infill density and layer printing orientation were investigated by performing in-plane compression tests, and the set of parameters that produced superior results for better EA was determined by analyzing the area under the curve and the welding between the filament layers in the printed object via FDM. The results showed that the printing parameters implemented in this study considerably affected the mechanical properties of the 3D-printed PET-G honeycomb structure. The structure with the upright printing direction and 100% infill density exhibited an extension to delamination and fragmentation, thus, a desirable performance with a long plateau region in the load-displacement curve and major absorption of energy.

On the Post-Processing of 3D-Printed ABS Parts

Application of Additive Manufacturing (AM) has significantly increased in the past few years. AM also known as three-dimensional (3D) printing has been currently used in fabrication of prototypes and end-use products. Considering the new applications of additively manufactured components, it is necessary to study structural details of these parts. In the current study, influence of a post-processing on the mechanical properties of 3D-printed parts has been investigated. To this aim, Acrylonitrile Butadiene Styrene (ABS) material was used to produce test coupons based on the Fused Deposition Modeling (FDM) process. More in deep, a device was designed and fabricated to fix imperfection and provide smooth surfaces on the 3D-printed ABS specimens. Later, original and treated specimens were subjected to a series of tensile loads, three-point bending tests, and water absorption tests. The experimental tests indicated fracture load in untreated dog-bone shaped specimen was 2026.1 N which was decreased to 1951.7 N after surface treatment. Moreover, the performed surface treatment was lead and decrease in tensile strength from 29.37 MPa to 26.25 MPa. Comparison of the results confirmed effects of the surface modification on the fracture toughness of the examined semi-circular bending components. Moreover, a 3D laser microscope was used for visual investigation of the specimens. The documented results are beneficial for next designs and optimization of finishing processes.

Novel Hybrid PETG Composites for 3D Printing

This paper is focused on the preparation of novel hybrid polymer composite materials for 3D filaments. As the reinforcing filler, expanded graphite, carbon fibers, and combinations thereof were used in various ratios up to 10%. The mechanical and thermal properties of virgin and recycled polyethylene phthalate glycol-modified (PETG) composite materials were determined. Almost all prepared composite materials were suitable for 3D printing and they have enhanced mechanical properties compared to the neat PETG matrices. Addition of the fillers to both polymer matrices has an only slight effect on the thermal stability, but the addition of carbon fibers significantly reduced the thermal expansion coefficient. The composites from cheaper recycled PETG have comparable properties to virgin PETG composites, which is of economic and ecological importance. New and cheaper materials can help expand 3D printing to manufacturing plants and the use of 3D printers for special applications.

Fire-extinguishing characteristics and flame retardant mechanism of polylactide foams: Influence of tricresyl phosphate combined with natural flame retardant

Extrusion and compression molding techniques were used to process polylactide (PLA) foams using a mixture blowing agent. Tricresyl phosphate (TCP) and natural flame retardants (NFR) from pumpkin (PK) and soybean (SB) were added to rigid PLA foams and the flame retardant properties of the foams were investigated. The effects of TCP content, types and amounts of NFR, and the ratio of TCP to NFR were determined on the physical, thermal and morphological characteristics of the foams. The fire-extinguishing characteristics and flame retardant mechanism of PLA foams with TCP were studied by thermogravimetric analysis-Fourier transform infrared (TGA-FTIR), scanning electron microscope (SEM), limiting oxygen index (LOI), and UL-94 techniques. The results revealed the efficiency of TCP as a flame retardant for PLA foams. Increased TCP levels contributed to a significant enhancement in fire-extinguishing characteristics. Phosphoric acid from thermal decomposition of TCP was a key factor in the proposed mechanism of flame retardation. Flame inhibition and retarded ignition of the PLA foams were achieved at all compositions of TCP and NFR. Due to the presence of compounds such as cellulose, phosphate, and silica, both PK and SB could be used as effective NFRs for PLA foams. All these characteristics promise extended applications for PLA foam in bio, circular, and green economies.

Nanocellular Foaming Behaviors of Chain-Extended Poly(lactic acid) Induced by Isothermal Crystallization

Recently, the fabrication of semicrystalline polymer foams with a nanocellular structure by supercritical fluids has been becoming a newly developing research hotspot, owing to their peculiar properties and prospective applications. In this work, a facile and effective isothermal crystallization-induced method was proposed to prepare nanocellular semicrystalline poly(lactic acid) (PLA) foams using CO₂ as a physical blowing agent. Styrene-acrylonitrile-glycidyl methacrylate (SAG) as a chain extender (CE) was introduced into PLA through a melt-mixing method to improve the crystallization behavior and melt viscoelasticity of PLA. The chain extension reaction between PLA and SAG occurred successfully as well as the branching and micro cross-linking structures were generated in chain-extended PLA (CPLA) samples, which were confirmed by Fourier transform infrared spectra, gel fraction, and intrinsic viscosity measurements. Owing to the nucleation effect of branching points and the restricted movement of PLA molecular chains by the formation of branching and/or microcross-linking structures, a large number of small spherocrystals were generated in CPLA samples, which was beneficial to produce nanocells. Nanocellular CPLA foams were prepared successfully, when the foaming temperature was 125 °C. As the SAG content increased, the cell size of various PLA foams decreased from 364 ± 198 to 249 ± 100 nm and their volume expansion ratio increased from 1.15 ± 0.05 to 2.22 ± 0.01 times, gradually. When the foaming temperature increased from 125 to 127 °C, an interesting transition from nanocells to microcells could be observed in CPLA foam with the CE content of 2 wt %. Finally, the formation mechanism of nanocells in various PLA foams was proposed and clarified using a schematic diagram.

Microcellular morphology evolution of polystyrene/thermoplastic polyurethane blends in the presence of supercritical CO2

In this article, a facile melt blending and solid batch foaming approach was proposed to prepare microcellular polystyrene/thermoplastic polyurethane (PS/TPU) blending foams with supercritical carbon dioxide (CO2). Compared with those of pure PS and pure TPU, an interesting phenomenon about the enhanced complex viscosity and storage modulus, as well as decreased loss factor of PS/TPU blends, was found. The solubility of CO2 in the PS/TPU blends was enhanced, owing to the CO2 solubilization effects of TPU. An interesting bimodal cell structure (BCS) was observed in the PS/TPU blending foams with the TPU content of 10, 15, and 20%. Consequently, a significant conclusion could be speculated that the generation of BCS in the PS/TPU blending system depended on not only the viscosity and morphology of the polymer blends but also the solubility and diffusivity of the CO2 as well as the type of cell nucleation. The thermal insulation property of PS foam was improved by the introduction of TPU.

Poly (lactic acid) blends: Processing, properties and applications

Poly (lactic acid) or polylactide (PLA) is a commercial biobased, biodegradable, biocompatible, compostable and non-toxic polymer that has competitive material and processing costs and desirable mechanical properties. Thereby, it can be considered favorably for biomedical applications and as the most promising substitute for petroleum-based polymers in a wide range of commodity and engineering applications. However, PLA has some significant shortcomings such as low melt strength, slow crystallization rate, poor processability, high brittleness, low toughness, and low service temperature, which limit its applications. To overcome these limitations, blending PLA with other polymers is an inexpensive approach that could also tailor the final properties of PLA-based products. During the last two decades, researchers investigated the synthesis, processing, properties, and development of various PLA-based blend systems including miscible blends of poly l-lactide (PLLA) and poly d-lactide (PDLA), which generate stereocomplex crystals, binary immiscible/miscible blends of PLA with other thermoplastics, multifunctional ternary blends using a third polymer or fillers such as nanoparticles, as well as PLA-based blend foam systems. This article reviews all these investigations and compares the syntheses/processing-morphology-properties interrelationships in PLA-based blends developed so far for various applications.

Multiple actions of poly(ethylene octene) grafted with glycidyl methacrylate on the performance of poly(lactic acid)

Poly(ethylene octene) grafted with glycidyl methacrylate (POE-g-GMA) was employed to improve the rheological and thermal properties, toughness, and foaming behaviors of poly(lactic acid) (PLA) through a chain extension effect.

The Effect of Compatibilization on the Properties and Foaming Behavior of Poly(ethylene terephthalate)/Poly(ethylene-octene) Blends

The methodology for improving the properties and foaming behavior of poly (ethylene terephthalate) (PET)/poly(ethylene-octene) (POE) blends through compatibilization was proposed. In this paper, PET/POE blends were prepared through a melt blending method, POE was employed as elastomer toughener, maleic anhydride grafted POE (mPOE) was selected as compatibilizer, and pyromellitic dianhydride (PMDA) was used as chain extender. The content of mPOE was changeable to study the effect of compatibility on crystallization behavior, toughness, dispersion morphology, and rheological behavior of PET/ POE blends. The results demonstrated that the crystallization peak of PET/POE blends shifted towards high temperatures from 196.97°C to 201.24°C with the content of mPOE increasing. The brittle-ductile transition for PET/POE blends occurred at the mPOE content in the range of 4–5 phr. The particle size of POE dispersed phase decline firstly and then was almost unchanged with an increasing content of mPOE. The storage modulus and complex viscosity of compatibilized PET/POE blends were obviously higher than that of uncompatibilized PET/POE blends. Then PET/POE blends were foamed using supercritical CO2 as physical blowing agent. The results showed that the cell size, cell density, and tensile properties of the PET/POE blending foams were affected by the content of mPOE strongly. With the content of mPOE, the cell size decreased and then kept stable as well as the cell density the trend of cell size increased then remained unchanged. In addition, the elongation at break of PET/POE blending foams was higher than that of the uncompatibilized PET/POE blending foam. PET/POE blending foams with fine cell morphology and good ductility could be achieved with a proper content of compatibilizer in the blends.

An investigation of the impact of an amino-ended hyperbranched polymer as a new type of modifier on the compatibility of PLA/PBAT blends

Poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends using amino-ended hyperbranched polymers (HBP) as modifiers were prepared by melt-mixing through a double-roller mill and injection molding. It was found that when the content of HBP was 2.5 phr, the elongation at break and the impact strength of PLA/PBAT blends both reached peak values. Moreover, by addition of HBP, the ΔTg of the blends was smaller. These results, together with Scanning electron microscope (SEM) images on the fractured morphology of the blends, indicate that the compatibility between PLA and PBAT is improved upon addition of HBP. The mechanism of the impact of HBP on the improvement of the compatibility between PLA and PBAT is proposed based upon Fourier transform infrared (FTIR) spectra.

Effects of Poly(butyleneadipate-co-terephthalate) as a Macromolecular Nucleating Agent on the Crystallization and Foaming Behavior of Biodegradable Poly(lactic acid)

The effect of a bio-based macromolecule, poly(butylene adipate-co-terephthalate) (PBAT), on the crystallization and foaming behavior of poly(lactic acid) (PLA) was evaluated. The crystallization kinetics results show that the addition of PBAT improved the crystallization of PLA by increasing the overall crystallinity and enhancing the crystal morphology of PLA. The massive crystallization zones may have prevented the escape of foaming gases to the surrounding area; the expansion ratio of the PLA foams increased from 4.87 to 10.94. Thus, a novel macromolecular crystallization nucleating agent for PLA was developed; the effect of the crystallization of PLA on its foaming behavior was also investigated. A high expansion ratio and finer cellular structure of PLA foam were obtained by optimizing the PBAT content.

Fine dispersion morphology of polystyrene/poly(ethylene terephthalate glycol) blending generation for controlled foaming behavior

Polystyrene/poly(ethylene terephthalate glycol) (PS/PETG) blends with different PETG contents were prepared using a Haake internal mixer at 190 °C.

Compatibility, morphology and mechanical properties of polylactic acid/polyolefin elastomer foams

In this study, different blends based on polylactic acid (PLA)/polyolefin elastomer (POE) and compatibilized PLA/POE was prepared by melt mixing. The compatibilizer glycidyl methacrylate-grafted-polyolefin elastomer (POE-g-GMA) was synthesized in a separate process. The Fourier transform infrared spectrum confirmed the reaction of POE and glycidyl methacrylate. Meanwhile, the morphology of dispersed phase was observed by scanning electron microscope. The results indicated that the compatibilizer has improved the compatibility and interfacial adhesion between PLA and POE phase. The rheological test results revealed that the introduction of compatibilizer could enhance the storage modulus and melt complex viscosity of PLA/POE blends. The foamability was studied in the presence of azodicarbonamide as a chemical blowing agent in the batch foaming process. Morphology of foams such as porous cell size, porous cell population density, and foam density were studied. It was found that the presence of POE in PLA foams has a great influence on their mechanical properties and the toughness. Addition of POE-g-GMA in samples increased elastic modulus of foams and decreased their strain at break.

Complex cellular structure evolution of polystyrene/poly (ethylene terephthalate glycol-modified) foam using a two-step depressurization batch foaming process

In order to decrease the cell size and maintain very high volume expansion ratio simultaneously, a methodology for the preparation of complex cellular structure (CCS) in polystyrene/poly(ethylene terephthalate glycol-modified) (PS/PETG) blend using two-step depressurization pressure batch foaming process was proposed. First, the optimum foaming temperature for PS and PS/PETG blend, respectively, were confirmed by one-step depressurization foaming process. Then, the CCS in PS and PS/PETG blending foam were fabricated by two-step depressurization foaming process at the optimum foaming temperature. The rheological properties of PS and PS/PETG blend were tested by dynamic rotational rheometer. The dispersion morphologies and foam morphologies were observed by scanning electron microscope. The lowest densities of PS and PS/PETG blending foams were obtained at the temperature of 136℃. The interfaces between PS and PETG could act as nucleation sites for the cell nucleation, which were helpful to fabricate the CCS. The CCS could be controlled by tuning the degree of the first-step depressurization and the holding time. The results showed that the large cells could be beneficial to decrease the foam density and the presence of small cells was beneficial to increase the cell number.

Photodegradation behavior and mechanism of poly(ethylene glycol-co-1,4-cyclohexanedimethanol terephthalate) (PETG) random copolymers: correlation with copolymer composition

Norrish type I and II mechanisms occurred in PETG copolymers. The inherent photostability of PETG decreased with increasing CHDM content. The higher CHDM content resulted in the higher crosslinking degree.

The Preparation and Characterization of Branching Poly(ethylene terephthalate) and its Foaming Behavior

Chain extension was an effective method for increasing the molecular weight, the melt strength and the foaming property of linear polymer. In this paper, pyromellitic dianhydride (PMDA) was used as chain extender to improve these properties of linear poly (ethylene terephthalate) (PET). The intrinsic viscosity, rheological and thermal characterizations of various PET samples was investigated. The results demonstrated that the increasement of the viscoelasticity at low frequencies was correlated to the raise of the intrinsic viscosity and the formation of long chain branching. These structural changes resulted in the decreasement of the crystallization temperature and melt temperature as well as the increase in the cold crystallization values with the increasing content of PMDA. The cellular morphology and expansion ratio of CEPET foams were also obviously improved by the introduction of PMDA. The expansion ratio of CEPET foam with the PMDA content of 1.0 phr would reach 31.78. In addition, the effect of the chain extension reaction time on the intrinsic viscosity, the rheological behavior, and foaming properties of PET were also studied. The results showed that the intrinsic viscosity, the rheological behavior, and the foamability of CEPET also decreased gradually with increasing chain extension reaction time, which should be attributed to the occurrence of more and more intense thermal degradation.

Balanced strength and ductility improvement of in situ crosslinked polylactide/poly(ethylene terephthalate glycol) blends

Polylactide/poly(ethylene terephthalate glycol) (PLA/PETG) blends with balanced strength and ductility improvement were achieved by crosslinking of PLA matrix and interfacial compatibilization via reactive melt blending.

Role of maleic- anhydride-grafted- polypropylene in supercritical CO2 foaming of poly (lactic acid) and its effect on cellular morphology

Poly (lactic acid)/maleic-anhydride-grafted-polypropylene (PLA/MAPP) blends were prepared by melt blending method. The effect of MAPP content on the dispersion morphology, thermal properties, and rheological behavior of PLA/MAPP blends was studied. Then PLA/MAPP blends were foamed using supercritical CO2 as physical blowing agent; and the cellular structure, cell size, as well as cell density were investigated. The results showed that of MA reacted with PLA, and thus a small amount of branched polymer would be formed. The branching structure strongly affected the rheological behavior, as well as the thermal properties of PLA. The blending morphology of PLA/MAPP blends also had a significant effect on the cell density of all the samples. The results indicated that homogeneous and finer cellular morphology for PLA/MAPP foams with high expansion ratio could be achieved with a proper content of MAPP in the blends.