Mechanical Blending Research Articles

Performance Evaluation of Asphalt Mixtures Modified with Recycled Polyethylene via the Wet Process

The plastics and asphalt pavement industries have shown increasing interest in recycling waste plastics in asphalt because of potential environmental benefits. One approach to incorporating recycled plastics in asphalt is the wet process, which requires mechanical blending of recycled plastics into the asphalt binder as polymer modifiers. This study was aimed at exploring the use of recycled polyethylene (rPE) and a reactive elastomeric terpolymer (RET), which was used as a potential compatibilizer to rPE, for asphalt modification. Moreover, the study evaluated the impact of both modifiers on the bond strength characteristics of asphalt-aggregate systems as well as on the rutting and cracking resistance of asphalt mixtures. To this end, a battery of laboratory performance tests was conducted on asphalt mixtures containing binders: one neat; two rPE modified; and one styrene-butadiene-styrene modified. One rPE modified binder was formulated by adding 3% rPE to a PG 58-28 neat binder, while the other was modified with 3% rPE, RET, and polyphosphoric acid. Test results indicated that the rPE-plus-RET modified binder yielded an asphalt-aggregate system with enhanced moisture resistance, before and after oxidative aging. When compared with the control mixture, using rPE alone or rPE plus RET for asphalt modification significantly improved the rutting resistance. However, the rPE and rPE-plus-RET modified mixtures were found to be more susceptible to intermediate-temperature fatigue cracking at both short-term and long-term aging conditions. Finally, adding rPE or rPE plus RET did not have a significant impact on the mixture reflective cracking and thermal cracking resistance after long-term aging.

Study on mechanical and tribological properties of cerium oxide/fluorine rubber composites

In order to study the effect of nanoscale cerium oxide (CeO2) on the basic mechanical properties of binary fluorine rubber (FKM), especially the tribological properties at different temperatures, CeO2/FKM composites were prepared by mechanical blending and hot molding process. The hardness test, tear test, uniaxial tension test, room-temperature rotational friction test and high-temperature reciprocating friction test of FKM and CeO2/FKM were performed. The surface morphology of the two materials after being rubbed was observed, and the rubber surface changes were analyzed by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results show that CeO2 particles can increase the hardness, matrix strength and resistance to external damage of rubber. Compared with pristine FKM, the tensile strength, elongation at break, anti-wear and anti-friction properties of CeO2/FKM composites have been effectively improved, and the enhancement of anti-wear properties of CeO2 reinforced FKM is more obvious under the condition of high temperature (200 °C). Therefore, the composites prepared by blending CeO2 with FKM can effectively improve the basic mechanical properties and tribological properties of FKM.

On 4D capabilities of chemical assisted mechanical blended ABS-nano graphene composite matrix

In past one decade thermoplastic composite matrix reinforced with graphene (Gr) (such as acrylonitrile butadiene styrene (ABS)-Gr, polyamide (PA)-Gr etc.) has been widely explored for 3D printing applications. But hitherto little has been reported on 4D capabilities of ABS-Gr (nano-particles) composite matrix prepared by chemical assisted mechanical blending. In this work, chemical assisted mechanical blending of ABS-Gr has been explored for 4D printing applications by considering magnetic field as stimulus with two way programming feature. The ABS-Gr composite was prepared with different weight proportions (10%, 15% and 20%) with chemical assisted mechanical blending. The twin screw extrusion (TSE) of composite lumps was carried to prepare 3D printing feedstock filament wires. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) was performed for morphological analysis of ABS-Gr composites. For 4D capabilities, composites of ABS and Gr were investigated for magnetic properties by performing vibration scanning magnetometry (VSM) test. Fourier transformed infrared spectroscopy (FTIR) of all proportions/compositions was performed to study bond strength analysis of ABS-Gr composite. Morphological analysis based on SEM/EDS has shown increase in carbon content as Gr content was increased. The VSM results showed that composite possesses magnetic properties and can be used for self assembly applications. Composite with composition/proportion ABS + 20%Gr has better magnetization, retentivity and coercivity. FTIR showed increase in bond strength of ABS-Gr composite due to uniform blending of nanoparticles. Further lower absorbance percentage outlined that the prepared composite matrix may be used for sensing low frequency signals in typical remote sensing applications.

Thermal oxidative degradation and ageing performance of silicone rubber filled with attapulgite

The natural attapulgite (NAPT) was disaggregated by high-pressure homogenization technology combined with extrusion process to prepare the attapulgite with disaggregated rod crystal bundles (DAPT) and large specific surface area of 133.7 m2/g. NAPT and DAPT were incorporated into the silicone rubber to obtain the composite NAPT-SR and DAPT-SR by mechanical blending method, respectively. After thermal oxidative ageing at 300 °C for 0.5 h, temperature for the 5% weight loss increased greatly from 385 °C of the neat silicone rubber to 396−399 °C with addition of NAPT and DAPT. NAPT and DAPT enhanced the interaction between the filler nanoparticles and rubber matrix thus inhibited the nanoparticle agglomeration. The conservation rate of the side methyl group in NAPT-SR and DAPT-SR was greatly improved after ageing. Therefore, the thermal oxidative degradation and ageing performance of the silicone rubber composites was significantly reinforced. Moreover, DAPT could greatly restrain the growth of nanoparticles after ageing. Therefore, DAPT-SR showed the better retention of tensile strength (40.6%), elongation at break (34.9%) and tear strength (30.1%) compared with the corresponding mechanical properties of the neat silicone rubber (10.6%, 7.4%, and 5.0%) after ageing.

Achieving structurally and functionally integrated electromagnetic shielding composites based on polyetheretherketone by sandwich structure

This study aims to prepare a structurally and functionally integrated polyetheretherketone/multi-wall carbon nanotubes (PEEK/MWCNTs) electromagnetic shielding composites by sandwich structure. The PEEK ultra-fine powder and MWCNTs mixed by mechanical blending were selected as the core-layer and PEEK-based film acted as the surface-layer. The results indicate that the electromagnetic shielding effectiveness (SE) and mechanical properties of the composites can be controlled by adjusting the ratio of PEEK which was chosen as the binder in the core-layer, the number of the core-layer and the composition of the surface-layer without sacrificing their thermal stability. Moreover, the specific electromagnetic shielding effectiveness (SSE), electrical conductivity, tensile strength and temperature of 5% weight loss (Td5%) of the optimized PEEK/MWCNTs composite reach 79.5 dB/mm, 1.8 S/cm, 93 MPa and 594°C, respectively. The performances of the above composite are obviously superior to those of the recently reported EMI composites. The improvements in the properties should be mainly attributed to the two factors: the dense conductive network formed by MWCNTs in the core-layer, and the good interface adhesion between MWCNTs-MWCNTs in the core-layer as well as between the core-layer and the surface-layer.

On correlation of rheological, thermal, mechanical and morphological properties of chemical assisted mechanically blended ABS-Graphene composite as tertiary recycling for 3D printing applications

ABSTRACT In past two decades, numerous 3D printing applications of acrylonitrile butadiene styrene (ABS) based mechanically blended composites for secondary (2°) recycling has been reported. But hitherto little has been reported on correlation of rheological, thermal, mechanical and morphological properties of chemical assisted mechanically blended ABS-Graphene (Gr) composite as tertiary (3°) recycling. In the present work chemical assisted mechanical blending of ABS and Gr nano particles (size 5–10 nm in three different weight proportions i.e. 10, 15 and 20%) has been reported. The effect of increasing Gr proportion was studied for establishing the correlation among rheological (melt flow index (MFI)) and viscosity), thermal, mechanical and morphological properties. The results of the MFI and viscosity testing showed that 20%Gr in ABS decreases the MFI and increases the viscosity of the composite matrix. The thermal testing showed that ABS+20%Gr composite have highest heat capacity (0.84 j/g) among selected proportions of matrix. As regards to mechanical properties are concerned, best settings are: ABS+20%Gr, temperature 210°C with 0.5 Nm torque for filament wire preparation on twin screw extruder (TSE). Morphological properties of filament wires were studied on metallurgical microscope to observe porosity percentage (%) in wire samples which was found minimum for ABS+20Gr.

Role of Well-Dispersed Carbon Nanotubes and Limited Matrix Degradation on Tribological Properties of Flame-Sprayed PEEK Nanocomposite Coatings

Abstract High-performance carbon nanotubes reinforced polyether ether ketone (CNTs/PEEK) nanocomposites display an excellent combination of mechanical, thermal, and tribological properties. It is a challenge to deposit high-performance CNTs/PEEK nanocomposite coatings via the coating techniques based on solution or melting processes due to low solubility and high melting point of PEEK for tribological applications. In this work, the CNTs/PEEK nanocomposite coatings with CNTs contents of 0.1, 0.5, 1.0, and 2.0 wt% were prepared by flame spraying of mixed PEEK and CNTs powders using mechanical blending (MB) and ultrasound dispersion (UD) methods. The flame-sprayed CNTs/PEEK nanocomposite coatings using UD powders preserved good CNTs dispersion, low porosity, and surface roughness, adhesive coating–substrate interfaces. The thermal degradation of PEEK ascribed to overheating of in-flight particles and flame-rescanning coatings was limited by good CNTs dispersion in flame-sprayed CNTs/PEEK nanocomposite coatings with an increase of CNT contents. The good dispersion of CNTs aided in initiating crystallization and confined crystalline growth resulting in high crystallinity degree and small crystallite size of PEEK matrix in the flame-sprayed CNTs/PEEK nanocomposite coatings. The uniform nanocomposite coatings with well-dispersed CNTs and few PEEK degradation in optimum content of 1.0 wt% preserved enhanced microhardness and superiorly tribological properties. The well-dispersed CNTs bonding with PEEK matrix enhanced the mechanical strength to restrict the generation of fatigue cracks from defects of voids, which promoted self-lubrication and wear resistance of flame-sprayed CNTs/PEEK nanocomposite coatings.

Versatile bimetal sulfides nanoparticles-embedded N-doped hierarchical carbonaceous aerogels (N-NixSy/CoxSy@C) for excellent supercapacitors and microwave absorption

The development of versatile functional composites is an intriguing and challenging approach to clean energy storage devices and electromagnetic pollution remediation. Herein, versatile bimetal sulfides nanoparticles-embedded N-doped 3D hierarchical carbonaceous aerogels was rationally constructed via controllable oxidation polymerization, mechanical blending and heat treatment methods. The encapsulation of bimetal NixSy/CoxSy nanoparticles and defects induced by N-doping can endow the fabricated aerogels with versatilities for excellent supercapacitors and microwave absorber. The dispersed and abundant active sites and easily diffused framework leads to remarkable electrochemical performances with a high specific capacitance of 2653.3 F g−1 at 1 A g−1 and excellent cycling stability of 89.2% at 10 A g−1 over 5000 cycles. More importantly, the assembled asymmetric supercapacitor of N-NixSy/CoxSy@C-900//AC displayed an energy density of 98.9 W h kg−1 at a power density of 371 W k g−1. Moreover, taking advantage of the unique heterostructures and well impedance matching, as-fabricated composites exhibited outstanding microwave absorption performance. The minimum reflection loss (RL) of - 47.2 dB was achieved at 11.6 GHz with the thickness of 2.5 mm, and an effective frequency bandwidth (RL<-10 dB) could be gained up to 3.7 (9.8–13.5) GHz. This work presents potential application in supercapacitor and microwave absorption.

Multifunctional NR/MWCNTs nanocomposites constructed via combining volume exclusion of SiO2 microspheres with interface reinforcement of tannic acid

Due to the intricate entanglement and strong π-π stacking interaction, carbon nanotubes are hard to be dispersed uniformly in polymer matrix, thereof it is difficult to produce high-performance and multifunctional polymer/multiwalled carbon nanotubes (MWCNTs) nanocomposites with low filler contents by traditional polymer processing technologies. Herein, the interspersed SiO2 microspheres (m-SiO2)/MWCNTs hybrid fillers (ISMH), which are not only dispersed easily in rubber matrix via mechanical blending but also have a biomimetic interface with the rubber matrix via natural tannic acid (TA), have been developed successfully. Benefiting from the volume exclusion of m-SiO2, a small amount of MWCNTs can form a dense three-dimensional (3D) network in natural rubber (NR) matrix, endowing NR/ISMH nanocomposites with high functionalities. When MWCNTs loading is 0.33 phr, the electrical conductivity of NR/ISMH nanocomposite can reach the equilibrium value ~10-4 S·cm−1. When MWCNTs loading is 1.67 phr, the thermal conductivity and compression temperature rise of NR/ISMH nanocomposite is ~0.32 W·m−1·K−1 and 9.3 °C, respectively, corresponding to an improvement of +22% and −28% relative to the neat NR matrix. Additionally, thanks to the biomimetic interface constructed by covalent and non-covalent bonds via TA, the NR/ISMH nanocomposites also have exhibited excellent mechanical properties. When the ISMH-30 loading (mass ratio of m-SiO2 : MWCNTs = 30: 1) is 20 phr, the comprehensive mechanical properties of NR/ISMH nanocomposite reach the best. The tensile strength, tear strength, elongation at break and DIN wear volume are 28.7 MPa, 43.7 MPa, 625% and 0.18 cm3, corresponding to an improvement of +58%, +16%, +11% and −31% relative to the neat NR matrix, respectively. In a word, the as-fabricated NR/ISMH nanocomposites have the advantages of low cost, high performance and versatile functions, endowing them with great potential applications in antistatic rubber products, vibration-isolated rubber products, and green tires, etc.

Study on mechanical and tribological properties of ternary fluororubber filled with four needles of zinc oxide

AbstractThis article deals with study of the influence of four‐needle zinc oxide (T‐ZnOw) on the basic mechanical properties of ternary fluororubber (FKM) and the frictional properties of FKM improved by four‐needle zinc oxide under different temperatures. T‐ZnOw/FKM composites were prepared by mechanical blending and hot molding after pretreatment with silane coupling agent. The hardness, tensile, tearing, rotating friction at normal temperature, and reciprocating friction at high temperature of FKM and T‐ZnOw/FKM were studied. The results showed that T‐ZnOw with needle‐like three‐dimensional (3D) structure can effectively decompose the point stress generated in the tensile process of the composite, and the uniform distribution of tensile force improves the fracture base point and final mechanical properties of the composite. Its unique 3D structure can reduce fatigue wear caused by extrusion plastic deformation of the matrix during the friction process. The friction coefficient and wear rate of materials were effectively reduced by the reduction of plastic deformation resistance and fatigue wear area in the process of friction. Especially at 200°C, the friction coefficient and wear rate of T‐ZnOw/FKM were reduced by 30% and 55.32%, respectively, by T‐ZNOW/FKM doping.

Microwave Absorption Properties of Unripe Plantain Husk, Polycaprolactone and Charcoal Powder Hybrid Nanocomposites Using Numerical Simulation at X-Band Frequency

Single bulk materials have lesser advantages compared to nano materials in the area of mechanical, electrical, dielectric, optical and thermal properties enhancement of polymer and hybrid of bio-composites. In this work, charcoal (CH), unripe plantain husk (UPH), and polycaprolactone (PCL) based microwave absorber were synthesized using both mechanical alloy and melt blend techniques, respectively. Different percentages of the prepared charcoal nanoparticles was introduced into the hybrid composites to study the effect on dielectric properties, shielding effectiveness, reflection loss and structural morphology in the frequency range of 8–12 GHz.. Findings showed that the sample with the highest amount of charcoal percentage had the best shielding effectiveness and dielectric constant. The value of dielectric constant gradually increased from 3.06 to 5.45 at the frequency range measured. The charcoal average particle size was estimated to be 21.42 nm using TEM analysis while the mean deviation of surface roughness ranged from 5.45 to 25.56 nm using atomic force microscope. The highest shielding effectiveness of the hybrid composites was obtained for the 30 wt% nano charcoal content with a value of -48.78 dB at 10 GHz. The complete dispersion and interaction of the charcoal with the PCL and UPH enhanced the dielectric constant, loss factor, hence making it potent in microwave absorption, shielding and radar applications.

Chlorinated butyl rubber/two-step modified montmorillonite nanocomposites: Mechanical and damping properties

Montmorillonite (MMT) was modified by ultrasound and castor oil quaternary ammonium salt intercalation method to prepare a new type of organic montmorillonite (OMMT). The surface structure, particle morphology, interlayer distance, and thermal behavior of the samples obtained were characterized. The modified OMMT was then added to chlorinated butyl rubber (CIIR) by mechanical blending, and a composite material with excellent damping properties was obtained. The mechanical experiment results of CIIR nanocomposites showed that the addition of OMMT improved their tensile strength, hardness, and stress relaxation rate. Compared with pure CIIR, when the content of OMMT was 5 phr (part per hundred of rubber), the tensile strength of the nanocomposite was increased by 677% and the elongation at break was also increased by 105.4%. The enhancement of this performance was mainly due to the dispersion of the nanosheets in CIIR rubber and the chemical interaction between the organoclay and the polymer matrix, which was confirmed by morphology and spectral analysis. OMMT also endowed a positive effect on the damping properties of CIIR nanocomposites. After adding 5 phr of OMMT, the nanocomposite owned the best damping performance, and the damping factor, tanδmax, was 37.9% higher than that of pure CIIR. Therefore, the good damping and mechanical properties of these CIIR nanocomposites provided some novel and promising methods for preparing high-damping rubber in a wide temperature range.

Mechanical, thermal, and friction properties of addition-type fluororubber co-filled with Al2O3 particles at high temperature

We investigate to improve the poor heat dissipation effect of seals under a high-temperature dynamic seal due to the low thermal conductivity of fluororubber (FKM). Al2O3 particles and FKM were modified by the mechanical blending method. Study its physical and mechanical properties and frictional wear properties at room temperature and high temperature. The mechanism of reciprocating friction and wear of composites at high temperature was analyzed in combination with the change of morphology and thermal conductivity of an electron microscope. The results show that the addition of Al2O3 particles can improve the physical and mechanical properties, friction properties, and thermal conductivity of FKM at high temperatures. We noticed that the wear resistance of Al2O3 itself and the increase of thermal conductivity of composites could improve the friction performance of composites at high temperatures.

Blending Between Aged and Virgin Asphalt Binders in Recycled Pavements: A Review Study

It is the intent of this work to provide a background on works on diffusion in asphalt binders and review the researches carried out at Imperial Oil and ExxonMobil Technology Centres which have investigated nature of diffusion in asphalt material. These investigations include diffusion between Reclaimed Asphalt Pavement (RAP) and virgin binders, progress of diffusion in laboratory-produced mix samples from rheology perspective, and impact of silo storage on diffusion progress between binders and its manifestation on the performance of plant-produced asphalt mix. RAP is a major component of manufacturing hot mix asphalt (HMA) in North America. RAP utilization promotes sustainability of asphalt industry with economic and environmental incentives for manufacturing process. Recent statistics in North America show that RAP content of HMA has increased from 15 to 20%. This RAP content increase further prompts development and implementation of science-based practices in manufacturing plants to achieve optimum quality of RAP containing mixes. Quality of blending between aged and virgin binders has been shown to significantly impact performance and durability of final mix in the field. It has been demonstrated that mechanical blending helps achieving effective contacts between RAP and virgin binder. However, diffusion is the dominant process to help blending between the binders. It has been demonstrated that binder diffusion follows Fick’s Law and the rate increases with temperature. Field verification indicated that around 12 hours is required to complete the diffusion at the typical hot mix production and silo storage temperatures. Mix samples with more-progressed diffusion exhibited improved rutting resistance and higher number of cycles to fatigue failure. Field work also validated that there is an optimum storage time during which diffusion is the dominant process impacting mix properties; but eventually mix hardening dominates due to oxidation, evaporation and absorption.

On Nanographene-Reinforced Polyvinylidene Fluoride Composite Matrix for 4D Applications

In past two decades, number of studies has been reported on 3D printing of polyvinylidene fluoride (PVDF) composite matrix. But hitherto, little has been reported on 4D applications of graphene(Gr)-reinforced PVDF for maintenance and repair of heritage structures, especially for self-assembly applications. In this work, mechanical blending of Gr (size 5-10 nm)-reinforced PVDF has been reported for 4D applications as possible on-line maintenance tool for heritage structures. The Gr was blended in four different weight proportions in PVDF matrix. The effect of varying Gr proportion was studied on basis of rheological properties (melt flow index (MFI) and viscosity) required for processing on open source fused deposition modeling (FDM) setup. The various proportions/compositions of the composites were also investigated for thermal stability based upon differential scanning calorimetry (DSC) analysis (required for heritage structure). The selected proportion/composition of feed stock filament were processed on twin screw extruder (TSE) followed by mechanical testing on universal testing machine (UTM). The results of the MFI and viscosity outlined that blending of Gr in PVDF decreases the MFI and increases the viscosity of the composite matrix. The DSC testing showed that PVDF-10%Gr composite have heat capacity of − 64 J/g (during heating cycle). The maximum peak strength of 43.01 N/mm2 was observed, while processing at screw temperature 195 °C with 0.3 Nm torque for filament wire preparation. Finally the 3D printing of selected composition/ proportion was also successful. The piezoelectric properties of composite were observed after direct current (DC) poling by dielectric constant measurement (D33 = 45 pC/N), which is sufficient for self expansion/contraction properties. The feed stock samples prepared were counter verified by performing morphological analysis. For self-assembly applications, vibration sample magnetometry (VSM) was performed. The results are also supported by Fourier transformed infrared spectroscopy (FTIR) analysis for ascertaining bonding characteristics corresponding to observed mechanical properties.

Bridging the gap between rubbers and plastics: a review on thermoplastic polyolefin elastomers

Thermoplastic elastomers (TPE) are studied for their unique properties of being easily processes and recycled. This paper focuses on the wide scope of thermoplastic polyolefin elastomers (TPO/TPE-O) which is one of the major classes of TPE. The performance of TPO is the cumulative effect of polyolefins and rubbers with the ease of processing due to the presence of thermoplastics. The study focuses on the classification of TPO, their routes of synthesis, composites, applications, and its impact on environment. The mechanical blending of polyolefins and conventional rubber was carried out to manufacture TPO. In further developments, the polyolefin elastomers (POE) were synthesized by copolymerization techniques to overcome the drawback of mechanical blending techniques. Environment-friendly blends of TPO are synthesized using industrial and municipal waste which includes scrap rubber tires, marble waste-filled polypropylene, computer body waste, etc. This technology will help in reducing the issue of landfills. The composites of TPO have been studied using different types of fillers which may be synthetic or bio-based. These include talc, carbon black, carbon nanotubes (CNT), Kenaf fiber, pineapple leaf fiber, etc. TPO have found their use in encapsulation, in electrical insulation, roofing, medical devices, and the automobile industry. Also, impact of using TPOs on environment is discussed here qualitatively.

Influence of β-phase stability in elemental blended Ti-Mo and Ti-Mo-Zr alloys

This paper investigated the improvement of mechanical properties for one of the most used biomaterials, titanium-based alloy. To improve its mechanical properties, molybdenum was chosen to be added to Ti and Ti-Zr alloys through a mechanical blending process. After homogenization of Ti (12, 15) Mo and Ti (12, 15) Mo-6 Zr, the compaction pressure and sintering temperature were varied to create pellets. Characterization has been done using scanning electron microscopy (SEM), X-ray diffraction (XRD), Vickers’s hardness, Archimedes test and ultrasonic method, and 3-point bending test. Micrograph of each pellet revealed the influence of Mo content that plays a prominent role in the variation of microstructure in the alloys Ti-Mo and Ti-Zr-Mo. The porosity and density were also influenced by changing the β-phase. EBSD analysis shows the increase in β-phase with the addition of Zr. The overall results indicated that the percentage of β-phase greatly affects the mechanical properties for the specimens.

A High Capacity All Solid‐State Li‐Sulfur Battery Enabled by Conversion‐Intercalation Hybrid Cathode Architecture

AbstractAs demands for electrochemical energy storage continue to rise, alternative electrochemistries to conventional Li‐ion batteries become more appealing. Here, an intercalation‐conversion hybrid cathode that combines intercalation‐type VS2 with conversion‐type sulfur chemistry to construct high performance solid‐state lithium‐sulfur batteries is reported. The layered VS2 nanomaterial features Li‐ion transport channels, metallic conductivity, and active capacity contribution, all of which provide an ideal platform for the solid state S/Li2S redox couple to unlock its high gravimetric capacity. The S/VS2/Li3PS4 hybrid cathode composite is prepared by a facile, low‐cost, and low‐energy mechanical blending process. The S/VS2/Li3PS4|Li3PS4|Li/In (or Li) all‐solid‐state cell exhibits sulfur utilization of ≈85%, with a Coulombic efficiency of close to 100%. High areal capacity up to 7.8 mA h cm−2 with an active material loading (S/VS2) as high as 15.5 mg cm−2 is achieved.

Limits to biomass productivity during fed-batch cultivation of Laminaria saccharina female gametophyte cells in a stirred-tank photobioreactor

This study compared the growth of Laminaria saccharina female gametophyte filamentous cell suspension cultures in a stirred-tank photobioreactor under batch and fed-batch nutrient addition modes over a 48-day cultivation period. Cultures were grown on GP2 artificial seawater medium (0.75 mM nitrate, N:P = 16:1) at pH 8.3 without iron or copper. Total equivalent nutrient loadings ranged from 0.5X to 9.1X GP2 for batch cultivation and 1.3X to 10.4X GP2 for fed-batch cultivation at delivery rates of 0.0067–0.16 mmol N L−1 day−1 based on nitrate. The multicellular, L. saccharina filamentous clumps were dispersed to nominal size of 100 μm by mechanical blending (~ 16,000 rpm, 5 s) prior to inoculation. Fed-batch addition of all nutrients enhanced biomass productivity by a factor of two over a batch cultivation process at equivalent total nutrient loadings in a stirred-tank photobioreactor. Peak productivity through fed-batch cultivation was 57 mg DCW L−1 day−1, and average final biomass densities exceeded 1800 mg DCW L−1, vs. 30 mg DCW L−1 day−1 and 800–900 mg DCW L−1 for batch cultivation. However, there was a limit to biomass productivity enhancement at cumulative nutrient loadings greater than 3X GP2 that was not the result of insufficient CO2 or light delivery. It is suggested that the formation of large, multicellular clumps approaching 1-mm diameter during stirred-tank cultivation may have ultimately reduced biomass productivity during fed-batch cultivation under nutrient-replete conditions. Therefore, future bioreactor processing strategies might consider mechanical blending to disperse the filament clumps during the cultivation process.

Economical conductive graphite‐filled polymer composites via adjustable segregated structures: Construction, low percolation threshold, and positive temperature coefficient effect

AbstractThe economical graphite‐filled thermoplastic urethane/ultra‐high molecular weight polyethylene (TPU/UHMWPE) composites with the segregated structure were constructed by the combination of mechanical crushing and melt blending method. The low percolation threshold of 1.89 wt% graphite in the adjustable segregated composites was obtained and high electrical conductivity was about 10−1 S m−1 at 10 wt% graphite loadings owing to the formation of three‐dimensional conductive networks. Moreover, when the graphite loadings were over the percolation threshold, the remarkable positive temperature coefficient (PTC) effect of electrical resistivity for TPU/UHMWPE‐Graphite composites were achieved, originating from the combined thermal motion of TPU and UHMWPE. Meanwhile, the outstanding repeatability of PTC effects was obtained after 5‐time cycles. Therefore, economical conductive polymer composites were still the promising field in the practical application of PTC materials.