催化超临界水氧化处理焦化废水

采用催化超临界水氧化技术处理武汉某焦化厂废水。Ir-Ta/堇青石催化剂在反应温度380～460℃,反应时间20～100 s,反应压力为22～30 MPa,过氧比0～4下,探究处理焦化废水的影响因素;用COD的去除率表示超临界水氧化降解有机物的进程对其进行动力学分析。结果表明,在超临界水中添加催化剂后的有机物去除效果明显高于无催化剂;反应温度、压力、时间和过氧比等影响因素与COD和氨氮去除率呈正相关;加入催化剂后,在反应压力24 MPa,过氧比为200%(2倍)时,反应活化能为46.26 kJ/mol,频率因子为73.20 s^(-1)。     

聚乳酸材料在3D打印中的研究与应用进展

综述了最近PLA材料在3D打印中的研究和应用进展。介绍了PLA的结构性质和合成方法,以及熔融沉积成型3D打印PLA材料的特性。重点介绍了最近3D打印PLA材料的改性和成型工艺研究。最后详细描述了3D打印PLA材料在生物医学领域中的应用进展,并对未来的发展方向和应用前景进行了展望。     

Enhancing the mechanical properties of 3D printed polylactic acid using nanocellulose

We report here a systematic investigation of the mechanical properties of polylactic acid (PLA) processed by fused filament fabrication (FFF) 3D printing vs PLA processed by compression molding. Our results show that the tensile strength and modulus of FFF-PLA is 49% and 41% lower, respectively, than compression molded samples of PLA. We also demonstrate here an approach to augment the mechanical properties of 3D printed PLA using nanocellulose. Incorporation of a small quantity (1 wt%) of cellulose nanofibers (CNF) was found to enhance the tensile strength and modulus of 3D printed PLA by 84% and 63%, respectively. X-ray microtomography was used to probe the morphology of 3D printed PLA and PLA/CNF composites. 3D printed PLA/CNF composites had significantly lesser voids as compared to neat 3D printed PLA. Differential scanning calorimetry study revealed that CNF can accelerate the nucleation and crystallization of 3D printed PLA leading to enhanced crystallinity. The thermal stability of 3D printed PLA/CNF composites was not compromised by the addition of CNF. The enhanced mechanical properties of 3D printed PLA/CNF composites can be ascribed to higher crystallinity and lesser defects.     

Measurement of the mechanical and dynamic properties of 3D printed polylactic acid reinforced with graphene

In this paper, three-dimensional (3D) printing system based on fused deposition modeling (FDM) is used for the fabrication of polylactic acid (PLA) specimens with and without graphene and to measure their dynamic mechanical properties. In particular, 3D printed PLA/graphene nanocomposites containing 10wt% graphene in PLA matrix were characterized by compression tests, cyclic compression tests, nanoindentation and modal tests. The results of the mechanical tests reveal that the incorporation of multifunctional graphene has improved the modulus, the strength and the hardness of the 3D printed nanocomposites. The damping as calculated by cyclic compression and modal tests was substantially increased compared to neat PLA samples.     

Improved part strength for the fused deposition 3D printing technique by chemical modification of polylactic acid

Fused deposition method (FDM) is popular as a plastic 3D printing technique. One of the drawbacks of this technology is its low bonding strength between layers, reducing through‐plane mechanical properties of a part compared with in‐plane strength within the layers themselves. This study focuses on altering the molecular structure of a polylactic acid by chain extension to increase the adhesion strength between layers, quantified by peel testing, in order to increase overall part strength. Four different samples were prepared in a high shear mixer, processed into filament and printed by a FDM‐type 3D printer. These samples were characterized for their thermal, rheological, mechanical and adhesion properties. The findings showed that the chain extender‐modified resins exhibited higher layer‐to‐layer adhesion strength as well as increased viscosity corresponding to an increasing degree of branching. The interlayer diffusion and entanglement of newly created branch chain ends improved bonding between the printed layers resulting in higher tensile properties. POLYM. ENG. SCI., 59:E59–E64, 2019. © 2018 Society of Plastics Engineers     

Mechanical and thermal properties of coconut shell powder filled polylactic acid biocomposites: effects of the filler content and silane coupling agent

The effects of the filler content and the coupling agent 3-aminopropyltriethoxysilane (3-APE) on the mechanical properties, thermal properties, and morphologies of polylactic acid (PLA)/coconut shell powder (CSP) biocomposites were investigated. It was found that increasing the CSP content decreased the tensile strengths and elongations at break of the PLA/CSP biocomposites. However, incorporating CSP increased their modulus of elasticity. The tensile strengths and modulus of elasticity of the PLA/CSP biocomposites were enhanced by the presence of 3-APE, which can be attributed to a stronger filler–matrix interaction. The thermal stabilities of the biocomposites increased with the filler content, and they were enhanced by 3-APE treatment. Meanwhile, the presence of CSP increased the glass transition temperatures (T _g) and crystallinities (X _c) of the PLA/CSP biocomposites at a filler content of 30 php. After 3-APE treatment, T _g and X _c of the PLA/CSP biocomposites increased due to enhanced interfacial bonding. The presence of a peak crystallization temperature (T _c) for the PLA/CSP biocomposites indicated that the CSP has a nucleating effect. The melting temperatures (T _m) and the T _c values of the biocomposites were not significantly affected by the filler content and 3-APE. PLA/CSP biocomposites that had been treated with 3-APE presented the strongest filler–matrix interaction, as confirmed by SEM.     

Optimization of the effectiveness of a three-dimensional electrode with respect to its ohmic variables

The effectiveness of three-dimensional electrodes is shown to be a function of its equivalent conductivity - the resultant of the effective conductivities of the solid matrix and the electrolytic solution. Criteria for optimizing the effectiveness by maximizing the equivalent conductivity are evaluated. High porosity, good matrix conductivity and high internal surface area are the basic requirements for design of an effective three-dimensional electrode.     

Studies regarding simulation process to static loading of the structures obtained from polylactic acid, 3D printed

Being a relatively new process, additive manufacturing needs many studies to be able to produce parts with the required properties. The aim of the paper is to establish whether, based on the physical and mechanical properties determined by tensile testing and by applying finite element analysis (FEA), viable results can be obtained regarding the behavior of the 3D printed structures at the different, static loading. The application of FEA for the tensile testing of 3D specimens led to the results close to those obtained by the tests. The values of the results obtained by simulation are higher by up to 7.2% compared with those recorded by tests. The simulation was applied both for the printed specimens from a single material and from two materials (multi-material). Regardless of the materials used in printing and the simulation method, the results of applying FEA are close to those recorded by testing.     

Modification of low-molecular polylactic acid by CaF2 nanoparticles: A new approach to change its material properties

Due to environmental problems and the increasing waste of resources, sustainable biodegradable plastics has become a great topic worldwide. In this communique, we present a simple low-cost synthesis to improve one of these typically used materials, PLA (polylactic acid). CaF₂ nanoparticles synthesized according the fluorolytic sol–gel synthesis in lactic acid give access to fine tune the material characteristics of LMPLA (low-molecular polylactic acid) due to a simply to apply polycondensation reaction of lactic acid monomers. Thus, for the first time, homo dispersed CaF₂ up to 15 wt % in PLA is synthesized as cubic nanomaterial improving the characteristics of a subsequently formed thermoplastic in comparison with a polycondensed PLA reference material. A detailed characterization of the synthesized material is provided by using X-ray imaging, TEM, ¹⁹F MAS NMR, (sol) XRD, MALDI-TOF, and nanoindentation. The results reveal a promising first step of a modification opportunity of LMPLA regarding melting point, elastic modulus, and hardness. This way it is possible to adjust material characteristics in a simple and inexpensive way, which might broaden the field of possible applications and make biodegradable plastics a more competitive alternative to conventional used ones. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47875.     

The crystallization behavior and mechanical properties of polylactic acid in the presence of a crystal nucleating agent

The crystallization behavior of polylactic acid (PLA) was studied in the presence of a crystal nucleating agent, ethylenebishydroxystearamide (EBH). The crystallization rate and crystallinity were significantly increased with addition of EBH. The isothermal crystallization half-time at 105°C was decreased from 18.8 minutes for neat PLA to 2.8 minutes for PLA with 1.0 wt % of EBH. The crystallinity of PLA with 1.0 wt % EBH was about 35% after 5-minute annealing at 105°C. Like neat PLA, the double melting peaks were also observed for nucleated PLA. The changes of the double melt peaks were investigated with various crystallization temperatures, heating rates, and annealing times. The heat deflection temperature (HDT) of nucleated PLA was up to 93°C after annealing. The correlation between crystallinity and HDT was demonstrated. A percolation threshold of crystallinity was found corresponding to HDT. The crystal size of nucleated PLA was significantly decreased with addition of EBH. The mechanical properties of annealed PLA blends simultaneously; showed improved modulus and impact strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Role of boric acid for a poly (vinyl alcohol) film as a cross-linking agent: Melting behaviors of the films with boric acid

We have investigated the role of boric acid as a cross-linking agent for a poly (vinyl alcohol) (PVA) film when the film is immersed in boric acid aqueous solution. DSC results show that the films with boric acid exhibit the higher glass transition temperatures than that of the PVA film without boric acid, when the films are dried after immersing in boric acid aqueous solutions with various boric acid concentrations, implying that boric acid penetrating into the films slows down the PVA molecular motion. Furthermore, simultaneous small-angle X-ray scattering and wide-angle X-ray diffraction measurements were performed on the melting processes of the PVA films with boric acid. We found that the crystallite size increase originated from melting and recrystallization do not occur for the PVA films with boric acid, whereas in the case of the PVA without boric acid the crystallite size is enlarged in both directions parallel and perpendicular to the chain axis via melting and recrystallization on melting. These indicate that chemical reactions of boric acid to the PVA molecular chains in amorphous regions resulted in cross-linking points take place in boric acid aqueous solutions, inhibiting recrystallization on melting, because the cross-links slow down the PVA molecular motion and must not be included in the crystalline domains.     

Comparison of 2D and 3D carbon/carbon composites with respect to damage and fracture resistance

The static mechanical responses of two- and three-dimensionally reinforced carbon/carbon composites (2D- and 3D-C/Cs) were compared. The mechanical properties examined included tensile and shear stress-strain (S-S) relations, and fracture behavior using compact tension and double edge notch configurations. Compared with 2D-C/Cs, 3D-C/Cs were shown to possess a similar tensile S-S relation, lower shear strength, higher ultimate deformation in shear, and much higher fracture resistance. The differences in shear and fracture resistance were shown to be derived from a weaker fiber/matrix interface and weaker bonding between fiber bundles in the 3D-C/Cs. These weak interface characteristics of 3D-C/Cs are due to the high value of residual stresses caused by the three-dimensional fiber constraint of 3D-C/Cs.     

Evaluation of systematic exploitation of tolerance with respect to a declared nutrient content in the production of fertilizers

A given tolerance value on the declared nutrient content of fertilizers is permitted by some national laws. A statistical method to assess systematic exploitation of tolerance values by single nutrient fertilizer producers is proposed. Production of superphosphate was selected as the case study. The method was tested on a yearly production, on randomly selected samples, and on a generated series of samples; it was found to be simple and reliable. The method is theoretically expected to be more reliable than the Wilcoxon test recommended by French law for normal distributions; it appears to fit better than the Wilcoxon test to uneven production of fertilizers.     

Improving the properties of polylactic acid by blending with low molecular weight polylactic acid‐g‐natural rubber

The low molecular weight (M_w) polylactic acid‐g‐natural rubber (PLA‐g‐NR) was synthesized by grafting the maleated natural rubber (MNR) with low molecular weight PLA at a weight ratio of 1:1 in toluene at 80°C. Two types of MNR (MNR10 and MNR20) having anhydride moieties of 10 and 20 wt%, respectively, were prepared. The reaction was followed by IR analysis. Next, the obtained PLA‐g‐NR was blended with pristine PLA using a twin‐screw extruder at PLA to PLA‐g‐NR weight ratios of 90:10, 80:20, 70:30, and 60:40 followed by compression to obtain specimens for testing. In case of 10 wt% PLA‐g‐NR having MNR10, it was found that blending of PLA with PLA‐g‐NR resulted in a 200% improvement in impact strength and twofold percent elongation at break (flexibility). Further SEM analysis confirmed that PLA‐g‐NR was compatible with PLA matrix. In contrast, NR was present as disperse particles which exhibited poor adhesion to PLA. From these findings, it was also found that PLA‐g‐NR was capable of improving the properties of PLA more than NR due to the fact that it exhibited higher compatibility. POLYM. ENG. SCI., 54:2770–2776, 2014. © 2013 Society of Plastics Engineers     

Exploring the impact of cellulose nanocrystals and annealing treatment on the interlayer bond strength of polylactic acid 3D printed composites

The extrusion-based 3D printing process offers advantages, such as high precision, low cost, high speed, simplicity, and the ability to deposit multiple materials simultaneously. However, using 3D printing composite materials with orthogonal anisotropy can limit the interlayer bonding strength of printed parts. In this study, the interlayer tensile strength of 3D-printed polylactic acid (PLA) was affected by adding 0.5 wt% cellulose nanocrystals (CNC) and 1.2 wt% di-cumyl peroxide (DCP) to PLA, and annealing at low temperature (373 K, 1 h). The effects of annealing and CNC were determined by mechanical testing, scanning electron microscopy, differential scanning calorimetry, expansion testing, rheological testing, and x-ray diffraction analysis. After annealing, the interlayer gap increased due to crystal shrinkage, leading to a 25.9% decrease in tensile strength. However, the addition of CNC and DCP significantly improved the flow properties of the sample, resulting in better interlayer bonding and a 52.7% increase in tensile strength.     

Mechanical properties with respect to water content of gelatin films in glassy state

Changes on the structural and molecular level of gelatin films induced by hydration below 25±3% water content (glass–rubbery transition at ambient temperature) were identified with DSC and FTIR spectroscopy. Three main stages of hydration were distinguished: (I) water bound by high-energy sorption centres; (II) structural water; (III) polymolecular layer water. The mechanical behaviour of gelatin films at each stage of hydration was characterized. Relaxation of the films during hydration was taken into account in the analysis of results. Hydrated gelatin films were characterized as brittle below the glass–rubbery transition at ambient temperature, however some improvement of mechanical properties related to a higher renaturation level was showed between 7 and 14% of water content in stage II (structural water).     

Eliminating the thermal degradation of polylactic acid by the modification of a macromolecular epoxy-type chain extender

A novel macromolecular epoxy chain extender was synthesized and used to modify the PLA resin for developing conventional melt extrusion technology. Fourier-transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and ¹H nuclear magnetic resonance (¹H NMR) characterized the successful synthesis. For the first time, the molecular weight $\left({\overline{M}}_w\right)$ plays a key role in preventing thermal degradation and chain extension were discussed experimentally. Macromolecular chain extender showed superior advantages in that the chain extender with higher molecular weight was easier to get the long chain branched (LCB) structure in the modification of PLA. The characterization by rotational rheometer, GPC, melt index, chemical titration, and differential scanning calorimeter (DSC), results demonstrate that the macromolecular epoxy chain extender could decrease the concentration of terminal carboxyl groups and increase ${\overline{M}}_w$ with only 0.5% dosage. At a concentration ≥2%, there were a large number of long chain branched structures in the chain extension system for modified PLA. It showed better melt strength and would influence the crystallinity of PLA which would significantly improve the processability of PLA, especially in high-temperature extrusion, blow molding, spinning, and other processing technologies and applications.     

The application of blocked polyfunctional isocyanate as a cross-linking agent in biodegradable extruded poly(lactic acid) foam

A polyfunctional isocyanate was prepared and was blocked by methanol to limit its premature reactivity with water or other nucleophiles. The methanol-blocked polyfunctional isocyanate was used as a cross-linking agent to improve the melt strength and foamability of poly(lactic acid) (PLA). The effect of the blocked polyfunctional isocyanate (BPI) content on the melting behavior, crystallization, degree of cross-linking, and melt strength of PLA was investigated, and the cellular morphologies of the PLA foams obtained by chemical foaming extrusion were studied, as well. The cold crystallization temperature increased with increasing BPI proportion and the melting peak changed from a single to multiple peaks upon the addition of BPI to PLA. The ∆H_c, ∆H_m, and X_c values initially increased and then decreased with increasing BPI content. It can be attributed to the effect of cross-linking on crystallization behavior of PLA. The degree of cross-linking increased with the BPI content of the PLA mixtures. The melt strength of the PLA mixture increased with increasing proportions of BPI, whose incorporation led to a decrease in the void fraction, cell size, and open cell content of the PLA foams but an increase in the cell density. When BPI was added to the PLA, the cell morphologies of the PLA mixtures were obviously enhanced.

     

Effect of silane coupling on the properties of polylactic acid/barium ferrite magnetic composite filament for the 3D printing process

Poly(lactic acid) (PLA)/barium ferrite (BaFe₁₂O₁₉) with different composition ratios was fabricated by magnetic composite filaments using an extrusion process for a 3D printer. The silane modified surface of BaFe₁₂O₁₉ was studied to observe the effect on the mechanical, morphology, thermal, and magnetic properties of magnetic composite filaments. The results showed that the silane treated surface BaFe₁₂O₁₉ not only enhanced the mechanical properties of magnetic composite filaments, but also improved adhesion and homogeneity between the BaFe₁₂O₁₉ filler and PLA matrix. Moreover, the thermal and magnetic properties of magnetic composite filaments were not obviously changed after adding silane treated surface BaFe₁₂O₁₉. The achievement of the magnetic composite filaments preparation with silane treated surface BaFe₁₂O₁₉ for the 3D printing process could become a guideline to develop and design other magnetic composites products in the near future.     

Formation of voids in composite laminates: Coupled effect of moisture content and processing pressure

Void formation as a result of prepreg moisture content and processing pressure during cure was experimentally investigated in thermosetting composite laminates. This was achieved by determining the void contents of eight‐ply laminates fabricated from TenCate^® BT250/7781 E‐glass/epoxy prepreg at processing pressures of 1.7, 3.0, 4.4, and 5.8 atm. At each processing pressure, three types of laminates were fabricated using: (i) unconditioned prepregs (direct from the storage bag); (ii) prepregs conditioned at 25% relative humidity; and (iii) 99% relative humidity. Dynamics of prepreg moisture uptake during conditioning was measured using a moisture analyzer and was shown to exhibit Fickian diffusion behavior. The void contents of the cured laminates were found to vary from 1.6% to 5.0% depending on humidity environment the prepregs were exposed and the pressure applied during fabrication. The void contents of all laminates were observed to approach an asymptotic value of ∼1.6% as pressure was increased. The experimental results indicated the processing pressure applied during fabrication was increasingly carried by the fiber bed, reducing resin pressure during cure. Therefore, an enhanced void formation model was proposed through the addition of a pressure reduction factor and an asymptotic void content term. The proposed model was found to accurately predict the void content of laminates made of prepregs exposed to constant/varying humidity environments and fabricated at a wide range of processing pressures. POLYM. COMPOS., 36:376–384, 2015. © 2014 Society of Plastics Engineers