Development of thermoplastic 3D printing feedstock utilising biomass

3D printing feedstock constituted by bio-based thermoplastic and biomass filler is increasingly gaining prominence for fused deposition modelling (FDM). Biomass fillers are abundantly available and sustainable resources, which are widely applied in biocomposites for producing cost-effective and sustainable materials. The incorporation of biomass filler in bio-based and biodegradable polylactide (PLA) has obtained considerable attention for FDM 3D printing application. In this thesis, hemp hurd (HH), the waste product of hemp fibre industry, and bamboo powder (BP), the waste product of bamboo-pole slicing and bamboo-plank sanding, were used as biomass fillers for the preparation of FDM feedstock by meltcompounding and extrusion. Due to the toughness decrease with the inclusion of biomass powder, the toughening modification of PLA biocomposites was investigated using poly(butylene adipate-co terephthalate, PBAT) combined with ethylene-methyl acrylate-glycidyl methacrylate random terpolymer (EGMA), a commercially-available core-shell acrylic impact modifier (BPM520), and polycaprolactone (PCL). The toughening efficacy was compared in PLA/BP biocomposite, and the processability and printability of the toughened biocomposites were examined. PDLA-PCL-PDLA (PCDL) tri block copolymers were investigated as compatibilizers for addressing the phase-separation of PLA/PCL blend and enhancing the toughness of PLA/BP/PCL biocomposite. The optimal toughening agent PBAT/EGMA was used for studying the effects of the biomass powder loading levels and particle sizes on PLA/HH and PLA/BP biocomposites as FDM feedstock. The melt flow, rheological, thermo-mechanical, and mechanical properties of biocomposite pellets, filament quality, and finish quality of FDM-printed parts were systematically investigated. The key findings of this research include understanding the relationship between toughness enhancement, loading levels and particle size distributions of HH and BP biomass species, and a major range of properties of PLA biocomposites, including melt flow, rheological, thermo mechanical, and mechanical properties of biocomposite pellets, filament quality, and finish quality of FDM printed parts, and the associated mechanisms. Also, PLA/HH and PLA/BP feedstocks were developed and appropriately applied in FDM 3D printing. Experimental results showed that PLA/BP biocomposite toughened by PBAT/EGMA exhibited higher toughness, superior filament quality, improved processability, and lower surface roughness than BPM520-toughened feedstock, and enhanced toughness than commercial PLA feedstock for both FDM-printed and injection-moulded (IM) specimens. PCDL efficiently improved the compatibility between PLA and PCL, leading to improved toughness. The increment in the toughness of PLA/BP biocomposite using PCL as toughening agent and PCDL as compatibilizer was insignificant. Among the three toughening agents, PBAT/EGMA was optimum with respect to toughness enhancement and processability, together with printability. Increasing biomass loading levels resulted in increased complex viscosity and decreased melt flow, while the FDM filament retained diameter tolerance (within ±0.03 mm) and roundness (0.04 mm) meeting the requirement in GB/T 37643-2019 standard. IM specimens filled with 40 phr HH exhibited 10.8% increase in tensile strength, 12% increase in flexural strength, 62.5% increase in flexural modulus, whereas 38.5% decrease in impact strength, compared to the base polymer matrix. FDM-printed parts with up to 30 phr HH or BP incorporation showed higher impact toughness than the parts fabricated from the commercial PLA filament control (46±2.5 J/m). Also, the FDM-printed parts exhibited greater dimensional accuracy (decreased shrinkage) than the samples from PLA control. The shrinkage of all PLA/HH samples was lower than that of PLA (0.33±0.04 %) and decreased from 0.30±0.06 % (PLA-HH-0) to 0.03±0.01 % (PLA-HH-40), indicating the dimensional accuracy improved with increasing HH loading. The porosity increased from 5.8% for PLA-HH-0 to 17.9% for PLA-HH-40, and 16.9% for PLABP-40. The increase in biomass loading levels and particle sizes did not change the average surface roughness (Ra and Rq) when the particle size of biomass was smaller than the printing layer thickness, while increased the peak-to-valley height (Rz and Rmax) of FDM-printed parts. HH and BP particle sizes exhibited opposite effects on the melt flow and complex viscosity (|η*|) at low frequency, increased particle size led to increased MFR and decreased |η*| for PLA/HH while decreased MFR and increased |η* for PLA/BP biocomposites. Larger particle size was advantageous for obtaining higher impact strength for both IM and FDM printed specimens for both PLA/HH and PLA/BP. The impact strength was improved from 41.3±3.0 J/m to 54.4±4.3 J/m for PLA/HH biocomposites. Impact strength was retained at around 55 J/m for FDM parts although the porosity increased from 4.86% to 9.85%, with concomitant particle size increase from 35 to 160 µm. PLA-BP-3 exhibited an impact strength of 13% and 38% higher than PLA-BP-1 for IM and FDM parts, respectively. This thesis contributes to the utilization of biomass filler in 3D printing for obtaining renewable and sustainable feedstock. This research reinforces the understanding of the influence of toughening modification, biomass filler contents, and particle size distributions on the melt flow, mechanical properties, processability, and printability of PLA biocomposites, and the underlying mechanisms. The potential of producing PLA biocomposites and application in FDM are investigated, the future work is discussed

Developmental Regulation and Function of AMPA Receptor Subunits in Chicken Lumbar Motoneurons

Ca2+ influx through ionotropic glutamate receptors regulates a variety of developmental processes including neurite outgrowth and naturally occurring cell death. In the CNS, NMDA receptors were originally thought to be the sole source of Ca2+ influx through glutamate receptors; however, AMPA receptors also allow a significant influx of Ca2+ ions. The Ca2+ permeability of AMPA receptors is regulated by the insertion of one or more edited GluR2 subunits into the receptors. Although Ca2+-permeable AMPA receptors are a familiar feature in developing neurons, the developmental function of these receptors during the formation of the nervous system has yet to be established. This study was designed to investigate the expression and functional role of Ca2+-permeable AMPA receptors in developing chicken spinal motoneurons. Our results demonstrate that chicken lumbar motoneurons express functional AMPA receptors as early as embryonic day (E) 5. Electrophysiological recordings of kainate-evoked currents indicate a significant reduction in the Ca2+ permeability of AMPA receptors between E6 and E11. During this developmental period, the Ca2+ permeability of AMPA receptors decreases three-fold. Reduction in the Ca2+ permeability of AMPA receptors is accompanied by increased expression of GluR2 mRNA in the spinal motoneuron pool. Changes in GluR2 mRNA expression occur in parallel to changes in GluR2 protein expression in the chicken ventral spinal cord. Changes in the Ca2+-permeability of AMPA receptors are not mediated by age-dependent changes in the editing pattern of GluR2 subunits. At early stages of development, functional AMPA receptors were composed of a combination of GluR3 and GluR4 subunits. mRNA analysis indicates that GluR4 is the most abundant subunit in the chicken ventral spinal cord between E6 and E11. Immunohistochemistry analysis of spinal cord sections also demonstrated that both GluR3 and GluR4 proteins are expressed at E6 and E11. Expression of Ca2+-permeable AMPA receptors regulates the maturation of dendritic outgrowth in developing spinal motoneurons. Measurements of dendritic length and branching pattern demonstrate significant changes in the dendritic morphology of spinal motoneurons between E6 and E11. Blockade of AMPA receptor activation with CNQX between E5 and E8 causes a significant increase in dendritic outgrowth in lumbar motoneurons, when compared with vehicle-treated embryos. Treatment of chicken embryos with CNQX between E8 and E11, when AMPA receptors become Ca2+-impermeable, has no affect on dendritic morphology. However, blockade of NMDA receptor activation with MK-801 causes a significant reduction in dendritic outgrowth of lumbar motoneurons by E11. These findings indicate that AMPA receptor activation between E5 and E8 limits dendritic outgrowth in developing motoneurons, whereas NMDA receptor activation is involved in dendritic remodeling after the establishment of synaptic contacts with sensory afferents

Estimation of Phonon Dispersion Relations Using Correlation Effects Among Thermal Displacements of Atoms

Neutron diffraction measurement of powder α-Fe sample at 295 K was carried out at the high resolution powder diffractometer installed at Japan Proton Accelerator Research Complex (J-PARC). Crystal parameters were determined from Rietveld analysis. The correlation effects among thermal displacements of atoms were estimated from a generalized equation based on the results of fomer diffuse scattering analysis. The force constants among atoms were obtained using an equation for transforming of the correlation effects to force constants. The force constants and the crystal structure of α-Fe were used to estimate the phonon dispersion relations, phonon density of states, and specific heat by computer simulation. The obtained force constants among first-nearest-neighboring atoms is 2.3 eV/Å2 at 295 K and the specific heat is 185 meV/K at 150 K. The calculated phonon dispersion relations and specific heat of α-Fe are similar to those obtained from inelastic neutron scattering and specific heat measurements, respectively. Received: 04 October 2014; Revised: 22 January 2015; Accepted: 30 March 201

Diffuse Neutron Scattering of KBr at Room Temperature and Its Application as Background Function in Rietveld Analysis

Diffuse neutron scattering from powder KBr was measured at room temperature. The oscillatory diffuse scattering is clearly observed. The diffuse scattering theory including correlation effects among thermal displacements of atoms is applied to background function in the Rietveld analysis. The observed scattering data are analyzed by including the correlation effects among thermal displacements of first, second and third nearest neighboring atoms. The inter-atomic distance and temperature dependence of the values of correlation effects is discussed

Graphene Based Waveguides

Graphene, which is well known as a one-atom thick carbon allotrope, has drawn lots of attention since its first announcement due to remarkable performance in mechanical, electrical, magnetic, thermal, and optical areas. In particular, unique properties of graphene such as low net absorption in broadband optical band, notably high nonlinear optical effects, and gate-variable optical conductivity make it an excellent candidate for high speed, high performance, and broadband electronic and photonics devices. Embedding graphene into optical devices longitudinally would enhance the light-graphene interaction, which shows great potential in photonic components. Since the carrier density of graphene could be tuned by external gate voltage, chemical doping, light excitation, graphene-based waveguide modulator could be designed to have high flexibility in controlling the absorption and modulation depth. Furthermore, graphene-based waveguides could take advantages in detection, sensing, polarizer, and so on

Force Constants of Cu Crystals from Diffuse Neutron Scattering Measurement

Diffuse neutron scattering measurement on Cu crystals was performed at 10 K and 300 K. Oscillatory forms were observed in the diffuse scattering intensities. The observed diffuse scattering intensities are analyzed by including the correlation effects among thermal displacements of atoms in the theory. Using the values of correlation effects among neighboring atoms and the values of Debye-Waller temperature parameter, force constants among first, second and third nearest neighboring atoms have been evaluated. The result of correlation effects in Cu crystals are compared to that of ionic crystal and semiconductor. The relation between correlation effects and the inter-atomic distance is not depending much on the crystal binding types. Received: 12 October 2010; Revised: 22 October 2010; Accepted: 16 December 201

Estimation of Phonon Dispersion Relations Using Correlation Effects Among Thermal Displacements of Atoms

Neutron diffraction measurement of powder α-Fe sample at 295 K was carried out at the high resolution powder diffractometer installed at Japan Proton Accelerator Research Complex (J-PARC). Crystal parameters were determined from Rietveld analysis. The correlation effects among thermal displacements of atoms were estimated from a generalized equation based on the results of fomer diffuse scattering analysis. The force constants among atoms were obtained using an equation for transforming of the correlation effects to force constants. The force constants and the crystal structure of α-Fe were used to estimate the phonon dispersion relations, phonon density of states, and specific heat by computer simulation. The obtained force constants among first-nearest-neighboring atoms is 2.3 eV/Å2 at 295 K and the specific heat is 185 meV/K at 150 K. The calculated phonon dispersion relations and specific heat of α-Fe are similar to those obtained from inelastic neutron scattering and specific heat measurements, respectively. Received: 04 October 2014; Revised: 22 January 2015; Accepted: 30 March 201

Expression and Significance of gp96 and Immune-related Gene CTLA-4, CD8 in Lung Cancer Tissues

Background and objective It has been proven that gp96 plays an important role in specific cytotoxic immune response which is involved in anti-tumor effect in the body. The aim of this study is to investigate the biological significance of heat shock protein gp96 and immune-related gene CTLA-4, CD8 expressions in lung cancer tissues of different progressive stages. Methods We used Envision immunohistochemistry method to detect the levels of expression of gp96, CTLA-4, CD8 in tissue microarray, which contained 89 primary lung cancer tissues, 12 lymph node metastasis lung cancer tissues, 12 precancerous lesions and 10 normal lung tissues, and analyzed the relationship between their expressions and clinicopathological parameters. Results (1) The positive rate of gp96 in primary lung cancer was remarkably higher than that in precancerous lesion and normal lung tissue (P < 0.05). The positive rate of CTLA-4 in primary lung cancer tissue and precancerous lesion was significantly higher than that in normal lung tissue (P < 0.05). The positive rate of CD8 in primary lung cancer tissue was significantly higher than that in normal lung tissue (P < 0.05). The positive rate of gp96 in CD8-positive lymphocytes in the high expression group was less than that in the low group (P < 0.05). (2) The positive rate of gp96 was closely related to sex, differentiation and clinical stage (P < 0.05), but not to age, gross type, histological type and lymph node metastasis (P > 0.05). The positive rate of CTLA-4 was closely related to age and differentiation (P < 0.05), but not to sex, gross type, histological type, clinical stage and lymph node metastasis (P > 0.05). CD8 expression was related to clinical stage (P < 0.05), but not to sex, age, gross type, histological type, differentiation and lymph node metastasis (P > 0.05). The positive rates of gp96, CTLA-4 were higher than that of CD8 in squamous cell carcinoma and SCLC, respectively. (3) There was positive correlation between gp96 and CTLA-4; there was negative correlation between gp96 and CD8, and there was negative correlation between CD8 and CTLA-4 (P < 0.05). Conclusion Gene expression of PD-L1 on lung cancer cell line can decrease the cytolytic effect of CTL on target cells

Force Constants of Cu Crystals From Diffuse Neutron Scattering Measurement

Diffuse neutron scattering measurement on Cu crystals was performed at 10 K and 300 K. Oscillatory forms were observed in the diffuse scattering intensities. The observed diffuse scattering intensities are analyzed by including the correlation effects among thermal displacements of atoms in the theory. Using the values of correlation effects among neighboring atoms and the values of Debye-Waller temperature parameter, force constants among first, second and third nearest neighboring atoms have been evaluated. The result of correlation effects in Cu crystals are compared to that of ionic crystal and semiconductor. The relation between correlation effects and the inter-atomic distance is not depending much on the crystal binding types. Received: 12 October 2010; Revised: 22 October 2010; Accepted: 16 December 201