Co-extrusion Technology Research Articles

3D composite printing: study of carbon fiber incorporation to different construction thermoplastic matrices in regard to dilatation characteristics

PurposeThe purpose of this paper is to clarify the relationship between the use of different polymer matrices for the preparation of composite materials, namely, polyethylene terephthalate-glycol (PET-G) and polyamide (PA), using Composite Fiber Co-Extrusion technology with the application of two types of carbon fibers, short and continuous. The aim of the study is also to extend the knowledge of the production of composite materials with a defined structure from the point of view of their influence on the microstructure and their physical-mechanical properties.Design/methodology/approachAs part of the experiment, four types of samples were prepared, namely, two types of samples with PA polymer matrix and two types with PET-G polymer matrix. All types contained short carbon fibers and always one set from each polymer matrix in addition to continuous carbon fibers. All types were prepared using the same 3D printing parameters to avoid any further influence. The samples were then tested for microstructure using microCT, mechanical properties using a tensile test and dilatation characteristics from the point of view of aerospace applications. Finally, the raw materials themselves were tested.FindingsThe paper provides insight into the influence of polymer matrix types on the physico-mechanical properties of 3D printed composites. The analysis confirmed that the physico-mechanical results varied with respect to the interface between the polymer matrix and the carbon fiber. The implications of the conclusions can be extended to the development of products in the aerospace and automotive sectors.Originality/valueThis study provides information for composite applications in the aerospace industry, focusing on evaluating dilatation characteristics within very low temperatures (−60 °C) when using carbon fibers (continuous carbon fibers, short carbon fibers and a combination of both) in two types of thermoplastic matrices. This perspective on materials characterisation for aerospace applications is a very important and unpublished approach within the 3D printing of composites. These characteristics are important parameters in the design of prototypes and functional samples with regard to the resulting behaviour in real conditions.

Reduction of polyketone membranes prepared by thermally induced phase separation with solvent co-extrusion for enhanced fouling resistance

This study utilized solvent co-extrusion technology and NaBH4 reduction to fabricate polyketone (PK) hollow fiber membranes with high water permeance and fouling resistance. Variations in reduction reaction time were explored to assess their impact on chemical composition, morphology, and properties. The results showed that the reduction reaction leads to the conversion of carbonyl groups on the membrane surface to hydroxyl groups, and with prolonged reaction time, the amount of hydroxyl groups on the membrane surface increases to a certain extent. The change in membrane chemical composition enhanced the hydrophilicity, while leaving the membrane morphology, mechanical properties, and separation performance largely unaffected. Static adsorption tests with bovine serum albumin (BSA) and E. coli exhibited distinct fouling behavior. While pristine PK membranes displayed significant BSA adsorption, PK reduction significantly reduced it. Both pristine and reduced PK membranes showed minimal E. coli attachment, likely due to weak interactions. Dynamic filtration tests demonstrated excellent flux recovery for reduced PK membranes, especially after 10 min of reduction, indicating superior fouling resistance with high flux recovery and low irreversible fouling, regardless of foulant type. These findings highlight a straightforward and efficient approach for producing high-performance membranes with exceptional fouling resistance suitable for practical applications.

Possibilities of Increasing the Durability of Dies Used in the Extrusion Process of Valve Forgings from Chrome-Nickel Steel by Using Alternative Materials from Hot-Work Tool Steels.

This study refers to an analysis of the dies used in the first operation of producing a valve forging from chromium-nickel steel NC3015. The analyzed process of manufacturing forgings of exhaust valves is realized in the co-extrusion technology, followed by forging in closed dies. This type of technology is difficult to master, mainly due to the increased adhesion of the charge material to the tool substrate as well as the complex conditions of the tools' operations, which are caused by the cyclic thermo-mechanical loads and also the hard tribological conditions. The average durability of tools made from tool steel WLV (1.2365), subjected to thermal treatment and nitriding, equals about 1000 forgings. In order to perform an in-depth analysis, a complex analysis of the presently realized technology was conducted in combination with multi-variant numerical simulations. The obtained results showed numerous cracks on the tools, especially in the cross-section reduction area, as well as sticking of the forging material, which, with insufficient control of the tribological conditions, can cause premature wear of the dies. In order to increase the durability of forging dies, alternative materials made of hot work tool steels were used: QRO90 Supreme, W360, and Unimax. The preliminary tests showed that the best results were obtained for QRO90, as the average durability for the tools made of this steel equaled about 1200 forgings (with an increase in both the minimal and maximal values), with reference to the 1000 forgings for the material applied so far.

Iron-Based Nanoplatforms Achieve Hepatocellular Carcinoma Regression Through a Cascade of Effects.

Ferroptosis is a regulated form of cell death characterized by iron-dependent accumulation of associated lipid peroxides (LPO), which can induce cell death when a certain level is reached. However, the extremely complex tumor microenvironment (TME) has the characteristics of antioxidant, even if it induces ferroptosis of tumor cells, its killing effect on tumor cells is still very limited. To solve this problem, we constructed a novel nanomaterials (GOx/EC@Fe3O4@CCM). We evaluated the anticancer effect of this nanomaterial in inhibiting tumor growth through comprehensive in vitro and in vivo experiments. We successfully synthesized GOx/EC@Fe3O4 by one-pan synthesis method, then coated the Hepatocellular carcinoma cell membrane on its surface by co-extrusion technology, and finally synthesized the GOx/EC@Fe3O4@CCM nanoplatforms. We characterized the compounds in terms of morphology, particle size, and Zeta potential. In addition, we also studied the anti-tumor effect of GOx/EC@Fe3O4@CCM nanoplatforms from the following aspects, including the performance test of the nanoplatform, the intracellular effect of the nanoplatform, the anti-tumor effect in vitro, the intracellular ROS analysis, the intracellular effect of EC, and the anti-tumor effect in vivo. The iron-based carriers in GOx/EC@Fe3O4@CCM nanoplatforms are released and produce ferrous ions (Fe2+) in an acidic environment. Due to the limitation of the endogenous level of hydrogen peroxide (H2O2), we introduced GOx into the TME or tumor cells. Under the catalysis of GOx, glucose reacted rapidly to produce a large amount of H2O2, which then combined with Fe2+ to produce a large number of Hydroxyl radical (·OH). Its toxicity leads to dysfunction of cell membrane and organelles, and then causes cell damage. EC inhibits Nuclear factor erythroid 2-related factor 2 (Nrf2) in cancer cells, which effectively down-regulates downstream gene products, including NAD(P)H quinone oxidoreductase 1 (NQO1) and heme oxygenase 1 (HMOX1). A series of chain reactions reduce the escape effect of oxidative stress (OS) and effectively maintain a high level of intracellular oxidation. Furthermore, it induces sustained and intense ferroptosis in tumor cells. Finally, the use of cancer cell membrane modified nanoplatforms due to the homology of membrane protein components improves the tumor cell targeting of the nanoplatforms, showing significant tumor cell inhibition and killing effect in vivo. The results showed that the GOx/EC@Fe3O4@CCM nanoplatforms successfully induced significant ferroptosis of Hepatocellular carcinoma cells through a cascade effect, and finally effectively promoted cancer cell regression.

Wetting-and scaling-resistant superhydrophobic hollow fiber membrane with hierarchical surface structure for membrane distillation

In this study, we address the challenge of wetting and scaling in membrane distillation (MD) by developing a robust superhydrophobic poly(vinylidene fluoride) (PVDF) hollow fiber membrane. To achieve this, we utilized co-extrusion technology and subsequent fluorination treatment to create micro-nanoscale surfaces. The fabrication process involved extruding a SiO2 suspension onto the outermost layer of a triple-orifice spinneret to create a hierarchical structure, followed by 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FAS) modification to lower the membrane surface energy. This resulted in a highly water-repellant membrane, as evidenced by contact angle measurements of 153°, 147°, and 141° for water, sodium dodecyl sulfate (SDS) solution (0.4 mM), and saline SDS solution (0.4 Mm SDS and 35 wt% NaCl), respectively, indicating increased resistance to liquid penetration. Through direct contact membrane distillation (DCMD) experiments, we demonstrated that the PVDF/FAS membrane exhibited excellent wetting resistance to seawater (3.5 wt% of NaCl) with SDS at varying concentrations. Furthermore, the membrane effectively hindered the CaSO4 scaling by reducing both heterogeneous nucleation and the tendency of bulk crystal deposition on the membrane outer surface. Overall, the developed approach for fabrication of superhydrophobic PVDF hollow fiber membrane presents a promising solution for facile and scalable manufacturing of anti-wetting and anti-scaling MD membranes. This advancement has significant implications for enhancing the practical application of MD technology.

Constructing a rigid-flexible grid structure for simultaneously strengthening and toughening bamboo flour/plastic composites through the introduction of continuous carbon fabric meshes via multi-layer co-extrusion

The defects of low strength, brittle fracture, and creep deformation of traditional wood–plastic composites (WPCs) significantly limit their applications as high-value-added products. This study aimed to develop advanced WPCs with high strength, toughness, and creep resistance via a structural design. A continuous rigid-flexible grid structure, sandwiched by carbon fabric mesh prepreg (CFMP) and casting film (MSF) with high toughness, was introduced into bamboo flour/high-density polyethylene composites (BPCs) via a multi-layer co-extrusion technology. The sandwiched grid structure was in-situ cured in the near-surface layers of BPCs to form a multi-layer composite (BPC-CFMP-F) during co-extrusion. The tensile strength, flexible strength, and impact strength of BPC-CFMP-F were 68.4 MPa, 89.0 MPa, and 22.5 kJ m−2, which are 138.3%, 96.4%, and 87.6% higher than those of BPCs, respectively, and the thermal expansion and 1000-hr creep strain of BPC-CFMP-F decreased by 45.8% and 61.7%, respectively. The simultaneous strengthening and toughening of BPCs were attributable to the rigid-flexible grid structure and the strong interfacial bonding between CFMP and BPCs and the surface- and core-layer BPCs through the grid of CFMP. Owing to these unique features, BPC-CFMP-F is a promising advanced composite with high strength, toughness, excellent creep resistance, and thermal stability for high value-added applications.

The effect of layer thickness ratio on the drug release behavior of alternating layered composite prepared by layer-multiplying co-extrusion.

Multi-layered drug delivery (MLDD) system has promising potential to achieve controlled release. However, existing technologies face difficulties in regulating the number of layers and layer-thickness ratio. In our previous works, layer-multiplying co-extrusion (LMCE) technology was applied to regulate the number of layers. Herein, we utilized layer-multiplying co-extrusion technology to modulate the layer-thickness ratio to expand the application of LMCE technology. Four-layered poly (ε-caprolactone)-metoprolol tartrate/poly (ε-caprolactone)-polyethylene oxide (PCL-MPT/PEO) composites were continuously prepared by LMCE technology, and the layer-thickness ratios for PCL-PEO layer and PCL-MPT layer were set to be 1:1, 2:1, and 3:1 just by controlling the screw conveying speed. The in vitro release test indicated that the rate of MPT release increased with decreasing the thickness of the PCL-MPT layer. Additionally, when PCL-MPT/PEO composite was sealed by epoxy resin to eliminate the edge effect, sustained release of MPT was achieved. The compression test confirmed the potential of PCL-MPT/PEO composites as bone scaffolds.

Effect of Mortise and Tenon Structure on the Properties of Wood Flour Polyvinyl Chloride-Laminated Veneer Lumber Co-Extruded Composites.

Core-shell composites with strong weather resistance, mechanical strength and creep resistance can be prepared using co-extrusion technology. Considering the weak bonding strength between core-shell interfaces, this study started from the concept of a mortise and tenon combination; three types of conical, rectangular and trapezoidal mortise and tenon joints were prepared, and their bending properties, long-term creep properties, interfacial bonding properties, and dimensional stability properties were tested. Results showed that the mortise and tenon structure could form a mechanical interlock between the outer-shell-layer polyvinyl chloride (PVC) wood-plastic composite (WPVC) and the inner-core-layer laminated veneer lumber (LVL), which could effectively improve the interface bonding property between the two layers. Among them, the trapezoidal mortise and tenon structure had the largest interface bonding force compared with the tapered and rectangular mortise and tenon structure, where the interface bonding strength reached 1.01 MPa. Excellent interface bonding can effectively transfer and disperse stress, so the trapezoidal mortise and tenon structure had the best bending properties and creep resistance, with a bending strength of 59.54 MPa and a bending modulus of 5.56 GPa. In the long-term creep test, the deformation was also the smallest at about 0.2%, and its bending properties, creep resistance and interface bonding performance were also the best. The bending strength was 59.54 MPa and the bending modulus was 5.56 GPa; in the long-term creep test, the strain curve was the lowest, about 0.2%. In addition, the mortise and tenon structure could disperse the stress of the inner shell LVL after water absorption and expansion, thus significantly improving the dimensional stability of the co-extruded composite after water absorption.

Alginate Core-Shell Capsules Production through Coextrusion Methods: Principles and Technologies.

This paper provides an overview of coextrusion methods for encapsulation. Encapsulation involves the coating or entrapment of a core material such as food ingredients, enzymes, cells, or bioactives. Encapsulation can help compounds add to other matrices, stabilize compounds during storage, or enable controlled delivery. This review explores the principal l coextrusion methods available that can be used to produce core-shell capsules through the use of coaxial nozzles. Four methods for encapsulation by coextrusion are examined in detail, including dripping, jet cutting, centrifugal, and electrohydrodynamic systems. The targeted capsule size determines the appropriate parameters for each method. Coextrusion technology is a promising encapsulation technique able to generate core-shell capsules in a controlled manner, which can be applied to cosmetic, food, pharmaceutical, agriculture, and textile industries. Coextrusion is an excellent way to preserve active molecules and present a significant economic interest.

Development of loose nanofiltration PVDF hollow fiber membrane for dye/salt separation

The fabrication of loose nanofiltration (LNF) membranes for effective separation of dye/salt wastewater mixtures remains a great challenge. In this study, a new method for preparing a LNF membrane is proposed by combining co-extrusion technology and chemical cross-linking. Poly(styrene maleic anhydride (PSMA), an amphipathic copolymer was first entrapped onto the outer surface of poly(vinylidene fluoride) (PVDF) hollow fiber membranes (HFMs) by spinning using a triple orifice spinneret. Subsequently, the prepared PVDF/PSMA membranes were cross-linked using polyethylenimine (PEI) or poly(allylamine hydrochloride) (PAH). Finally, the chemical structure, morphology, hydrophilicity, zeta potential, and pore size were studied systematically. The small pore size and strong positive charge of the prepared membranes contributed to the high rejection of various dyes (>99 %) and low salt rejection (<8.5 %). The prepared membranes also exhibited excellent stability during long-term filtration. Antifouling experiments demonstrated that the prepared LNF membrane had good fouling reduction properties against bovine serum albumin (BSA) and lysozyme (LYZ). This study provides new perspectives for the design of useful LNF HFMs for the treatment of dye/salt wastewater mixtures.

Optimization of core-shell capsules properties (Olive oil/alginate) obtained by dripping coextrusion process

Dripping coextrusion technology was used to produce core-shell capsules (olive oil/alginate). Mathematical models were developed to study isolated, and interactions impacts of calcium chloride concentration (37.5–187.5 g. L−1), alginate and oil total feed rate (40–108 g.min−1), and dripping height (7–15 cm) on capsules characteristics. Therefore, capsules diameter, sphericity, rupture strength, and encapsulation payload were studied with response surface method using Doehlert matrix. A study showed that capsules characteristics were mainly impacted by calcium chloride concentration and alginate/oil total feed rate. The role of calcium ions on shell structuration mechanisms was highlighted. The process was successfully optimized using multi-response method through desirability function. A mathematical model was developed for the prediction of diameter, sphericity, rupture strength, and encapsulation payload of capsules produced by dripping coextrusion. This model will be useful for further process applications such as fish-egg-like capsules in food industries and “liquid pearls” in cosmetic industries.

Controlled directional drug release from poly(ε-caprolactone)/polyethylene oxide/metoprolol tartrate composites with multi-layered structures

Nowadays, it is a challenge to achieve the controlled directional release of multi-layered dosage forms due to the difficulty of flexible and controllable regulation of the layered structure. Herein, we utilized layer-multiplying co-extrusion (LMCE) technology to construct poly(ε-caprolactone) (PCL)/polyethylene oxide (PEO)/ metoprolol tartrate (MPT) composites with controlled multi-layered structures, followed by the surface coating with epoxy resin. In vitro release results indicated that the release behavior of PCL/PEO/MPT composites could be flexibly modulated by the choice of uncoated surface and the number of layers. The release profile of PCL/PEO/MPT composites with PCL/PEO/MPT layer as the upper face (uncoated surface) conformed to classical Higuchi diffusion model. MPT of surface layer was released first, followed by the diffusion of MPT of inside layer in a layer-by-layer manner. The more layers, the narrower the diffusion channel, resulting in a lower release kinetics parameter. In conclusion, LMCE technology should possess great potential for the preparation of controlled directional drug release dosage forms.

Controlled metoprolol tartrate release from poly(ε-caprolactone)-poly(ε-caprolactone)/polyethylene oxide/metoprolol tartrate composites with alternating multi-layered structures prepared through layer-multiplying co-extrusion

Multi-layered structure design has provided a promising and powerful strategy for the fabrication of controlled-release dosage forms. However, a convenient and effective preparation technology is still urgently needed. Herein, we applied layer-multiplying co-extrusion (LMCE) technology to construct poly(ε-caprolactone)-poly(ε-caprolactone)/polyethylene oxide/metoprolol tartrate (PCL-PCL/PEO/MPT) composites with alternating multi-layered structures in one step. The layer number could be doubled by an addition of layer-multiplying element. The degradation analysis indicated that fewer PCL layers were beneficial to the dissolution of PEO and increased the pore size in the matrix. The in vitro release results suggested the MPT encapsulated in PEO aggregates was released gradually in a layer-by-layer manner, and the MPT release was flexibly modulated by the number of PCL layer and PEO content. Additionally, methyl thiazolyl tetrazolium assay presented a potential application of PCL-PCL/PEO/MPT composites in tissue engineering. The LMCE technology should have great potential for the preparation of controlled-release dosage forms.

A Comprehensive Review on the Application of 3D Printing in the Aerospace Industry

Additive manufacturing is a process wherein a three-dimensional object is created layer-by-layer. It offers adaptability to the geometrical complexity and customizability of the design, which is difficult to manufacture using conventional manufacturing. The aerospace industry is one of the sectors that first adopted additive manufacturing, particularly three-dimensional printing (3D printing) in the production of aircraft parts such as rocket engine components, oil fuel tanks, environmental control system ducting, combustor liner, custom cosmetic aircraft interior components, and unmanned aerial vehicle (UAV) components. The aircraft's most common materials used in the 3D printing prototype parts are acrylonitrile butadiene styrene (ABS) thermoplastic, carbon-fiber and thermoplastic composite, and nylon 12 using selective laser sintering, fused deposition modeling, or composite filament co-extrusion technology. One of the aerospace industry's challenges is ensuring the efficiency and quality of aircraft structural parts that typically require complicated manufacturing due to their complexity and variability of function. Additive manufacturing is seen to respond to this challenge by developing and prototyping 3D printed parts and exploring practical 3D printing technologies.

Improving the low-temperature toughness of PPR pipe by compounding with PERT

In this research, multi-layer co-extrusion technology was adopted to prepare Polypropylene random copolymer (PPR)/Polyethylene of raised temperature resistance (PERT) composite pipes. The structures and mechanical properties of PPR/PERT composite pipe were investigated by scanning electron microscopy (SEM), Dynamic thermomechanical analysis (DMA) and impact test systematically. It was found that PPR and PERT obey different deformation mechanism at low temperature. When tested at -50 °C which is lower than the glass transition temperature (Tg) of PPR, the molecular chains of PPR are frozen, which leads to the high notch sensitivity and extremely low impact strength of PPR/PERT pipe. Nevertheless, PERT whose Tg is about -78 °C could effectively inhibit the initiation and propagation of crack and therefore improve the low-temperature toughness of PPR/PERT composite pipe significantly. Furthermore, we found that the composite pipe of PPR/PERT-2:1 could combine the stiffness of PPR and the toughness of PERT most effectively, resulting in the optimized performances of PPR/PERT pipe.

Biopesticidal silo bag prepared by co-extrusion process

Silo bag technology is used for storing grains in a hermetic plastic structure. The major limitation of this structure is resistance to improper handling and external aggression, thus promoting pest incidence due to alterations in its internal atmosphere. In this study, we developed a biopesticidal silo bag consisting of a co-extruded three-layer film made of polyethylene and essential oil of Mentha piperita (7% w/w) in the inner layer. A film with the same structure but without essential oil was produced to be used as a control. The presence of the biopesticide in the silo bag was confirmed by FTIR-spectroscopy. Thus, mechanical, optical and chemical properties were evaluated. Diffusion coefficient of biopesticide from silo bag at 15, 25 and 35 °C was estimated as 6.4 ± 0.1 × 10-11, 1.45 ± 0.17 × 10-10 and 1.30 ± 0.2 × 10-10 cm2/s, respectively. Finally, the biopesticide silo bag was tested against Rhyzopertha dominica, primary pest of stored grain, showing 100 % of mortality during the time assayed (7 days). Hence, the incorporation of biopesticide by co-extrusion technology (low-cost and efficient machinery) into the inner layer of a silo bag could help to replace synthetic pesticides and avoid manipulation of these in the field, preventing biotic infestation.

Biodegradable PLA/PBSA Multinanolayer Nanocomposites: Effect of Nanoclays Incorporation in Multinanolayered Structure on Mechanical and Water Barrier Properties.

Biodegradable PLA/PBSA multinanolayer nanocomposites were obtained from semi-crystalline poly(butylene succinate-co-butylene adipate) (PBSA) nanolayers filled with nanoclays and confined against amorphous poly(lactic acid) (PLA) nanolayers in a continuous manner by applying an innovative coextrusion technology. The cloisite 30B (C30B) filler incorporation in nanolayers was considered to be an improvement of barrier properties of the multilayer films additional to the confinement effect resulting to forced assembly during the multilayer coextrusion process. 2049-layer films of ~300 µm thick were processed containing loaded PBSA nanolayers of ~200 nm, which presented certain homogeneity and were mostly continuous for the 80/20 wt% PLA/PBSA composition. The nanocomposite PBSA films (monolayer) were also processed for comparison. The presence of exfoliated and intercalated clay structure and some aggregates were observed within the PBSA nanolayers depending on the C30B content. A greater reduction of macromolecular chain segment mobility was measured due to combined effects of confinement effect and clays constraints. The absence of both polymer and clays interdiffusions was highlighted since the PLA glass transition was unchanged. Besides, a larger increase in local chain rigidification was evidenced through RAF values due to geometrical constraints initiated by close nanoclay contact without changing the crystallinity of PBSA. Tortuosity effects into the filled PBSA layers adding to confinement effects induced by PLA layers have caused a significant improvement of water barrier properties through a reduction of water permeability, water vapor solubility and water vapor diffusivity. The obtaining barrier properties were successfully correlated to microstructure, thermal properties and mobility of PBSA amorphous phase.

Experimental investigation of flame retardancy and mechanical properties of APP/EG/TPU multilayer composites prepared by microlayer coextrusion technology

AbstractIn this paper, ammonium polyphosphate(APP)/expandable graphite(EG)/thermoplastic polyurethane (TPU) composites were prepared by microlayer coextrusion technology, APP and EG fillers had good synergistic flame retardancy and excellent dispersion in TPU matrix, which greatly improved the flame retardancy and mechanical properties of multilayer composites. The dispersion of APP and EG in TPU was characterized by using SEM, the flame retardancy of composites was characterized by using UL94 and LOI, the thermal stability of composites was characterized by using TGA and DTG, and tensile test was used to characterized the mechanical properties of composites. SEM showed that the microlayer coextrusion technology significantly improved the dispersion of APP and EG in TPU. As showed by the experimental results, the vertical combustion level of ordinary blended composites reached V‐2 after adding only one kind of filler either APP or EG, and the vertical combustion level of ordinary blended composites reached V‐0 with APP and EG applied together, while the vertical combustion level of microlayer coextruded composites all reached V‐0 when the total addition of APP and EG was 15%. In particular, the LOI value of microlayer coextruded composites was 30.9%, while the LOI value of ordinary blended composites only was 27.9% when APP: EG = 1: 1. At this time, the flame retardancy level of APP/EG/TPU composites was the best. In addition, the thermal stability and mechanical properties of microlayer coextruded composites were far superior to ordinary blended composites. In conclusion, the synergistic flame retardancy of APP and EG fillers and the dispersion of APP and EG fillers in TPU matrix played a significant role in enhancing flame retardancy and mechanical properties.

Strategy for constructing electromagnetic interference shielding and flame retarding synergistic network in poly (butylene succinate) and thermoplastic polyurethane multilayered composites

Fabricating electromagnetic interference (EMI) shielding materials with excellent flame retarding properties is significant to attenuate undesirable electromagnetic waves caused by electronic devices and simultaneously improve the flame safety of the electronic components. Herein, a novel EMI shielding composite with multilayered structure was fabricated at a low particle loading via layer-multiplying coextrusion technology. Especially, within the multilayered composites, poly (butylene succinate) (PBS) filled with carbon nanotubes (CNTs) was used to construct conducting layer while thermoplastic polyurethane (TPU) filled with intumescent flame retardants (IFRs) and CNTs was used to construct synergistic flame-retarding layer. The content of CNTs and IFRs in the whole system were below 4 wt% and 20 wt%, respectively. Morphological observation demonstrated the alternating multilayered structure and the selective distribution of IFRs and CNTs. Besides, by tailoring the layer numbers, the composites showed tunable EMI shielding and flame retarding performances. With regard to EMI shielding performance, the absorption-dominated average EMI shielding effectiveness (SE) values of both 8- and 16-layer specimens exceeded 30 dB in the range of 8.2–12.4 GHz. Furthermore, superior flame retardancy with prompt self-extinguishment and anti-dripping was achieved in these specimens owning to the production of continuous and foaming carbonaceous structure among layers. Especially the 8-layer specimen, the UL-94 rating was categorized in V-0. Consequently, this work provided a promising and facile route to fabricate polymeric composites simultaneously possessing excellent EMI shielding and flame-retarding properties to fulfill the stringent requirements in practical application.

Microencapsulation of Bifidobacterium animalis subsp. lactis BB-12 with mannitol

Bifidobacterium animalis subsp. lactis BB-12 (BB-12) was microencapsulated using co-extrusion technology with chitosan coating and the incorporation of mannitol as prebiotic. Optimization of coating material chitosan concentration (0–0.5% w/v) and mannitol concentration (0–5% w/v) as prebiotic were performed to determine the formulation that produces beads with desired properties. The microencapsulation efficiency (MEE) of free and microencapsulated BB-12 (with and without mannitol) were determined. All forms of BB-12 further subjected to sequential digestion in simulated gastric juice (SGJ, pH 2.0) for 2 hours and simulated intestinal juice (SIJ, pH 7.5) for 3 hours. The results indicated that 0.4% (w/v) of chitosan coating and 3% (w/v) of mannitol were the optimum concentrations to produce microencapsulated BB-12 with the highest MEE of 89.15% and the average bead size of 805 µm. The BB-12 beads produced through co-extrusion were spherical with a smooth surface. Throughout the five hours sequential gastrointestinal digestion, both microencapsulated BB-12 with and without mannitol were able to maintain their viable cell count at least 106 CFU/g at the end of the incubation. The presence of prebiotic mannitol showed a significant protective effect on the microencapsulated BB-12 during gastrointestinal transit.