A novel material for lightweight concrete production

This paper presents the results of an experimental study on the effects of using recycled waste expanded polystyrene foam (EPS), as a potential aggregate in lightweight concrete. In this study, thermally modified waste EPS foams have been used as aggregate. Modified waste expanded polystyrene aggregates (MEPS) were obtained by heat treatment method by keeping waste EPS foams in a hot air oven at 130 °C for 15 min. Effects of MEPS aggregate on several properties of concrete were investigated. For this purpose, six series of concrete samples were prepared. MEPS aggregate was used as a replacement of natural aggregate, at the levels of 0%, 25%, 50%, 75%, and 100% by volume. The density of MEPS is much less than that of natural aggregate; MEPS concrete becomes a lightweight concrete with a density of about 900–1700 kg/m³. The 28-d compressive strengths of MEPS concrete range from 12.58 MPa to 23.34 MPa, which satisfies the strength requirement of semi-structural lightweight concrete.     

Thermal,mechanical and rheological properties of polylactide toughened by expoxidized natural rubber

This paper concerns on the use of epoxidized natural rubber (ENR) as toughening agent for polylactide (PLA). ENR with epoxidation content of 20 mol% (ENR20) and 50 mol% (ENR50) were separately melt blended with PLA using an internal mixer. DSC results suggested that PLA/ENR blends were amorphous after melt blending while they were crystalline and revealed two melting peaks in the thermograms after being annealed at 100 °C. Mechanical tests showed that the introduction of ENR reduced the tensile modulus and strength but enhanced the elongation and the impact strength of PLA. The impact strength of the 20 wt% ENR20/PLA and ENR50/PLA blends increased to 6-fold and 3-fold, respectively, compared to that of pure PLA. This enhancement was due to a good interfacial adhesion between ENR and PLA. Both ENR20/PLA and ENR50/PLA blends performed very strong shear thinning behavior, and the complex viscosity, storage and loss modulus of the blends also increased after blending with ENR.     

Microcellular extrusion foaming of poly(lactide)/poly(butylene adipate-co-terephthalate) blends

Foamed poly(lactide) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends were processed via the microcellular extrusion process using CO₂ as a blowing agent. Talc has been added to promote heterogeneous nucleation. Two types of PLA/PBAT blend systems were investigated: Ecovio, which is a commercially available compatibilized PLA/PBAT blend; and a non-compatibilized PLA/PBAT blend at the same PLA/PBAT ratio (i.e., 45:55 by weight percent). Six different formulations were investigated: pure PLA, PLA-talc, Ecovio, Ecovio-talc, non-compatibilized PLA/PBAT blend, and non-compatibilized PLA/PBAT-talc. The effects of various processing parameters such as die temperature, talc and compatibilization on various foaming properties such as cell morphology, volume expansion ratio (VER), open cell content (OCC) and crystallinity were investigated. As per the DSC thermograms, it was observed that compatibilization has merged the two distinctive melting peaks of PLA and PBAT into a single peak while lowering the peak temperature. In general, the addition of talc has decreased the average cell size and VER and increased the cell density and crystallinity; however, it has varying effects on the open cell content. Compatibilization has reduced the average cell size and volume expansion but increased the cell density and had varying and no effects on the OCC and crystallinity, respectively. Similar to compatibilization, the die temperature was found to have varying and no effects on the OCC and crystallinity, respectively. Except for PLA and non-compatibilized PLA/PBAT blend, the cell size and VER of all other formulations did not vary much throughout the entire temperature range (130–150 °C). The cell density was found to be insensitive to die temperatures except for Ecovio and Ecovio-talc.     

Investigation of the electromagnetic characteristics of cement based composites filled with EPS

Due to the electromagnetic transparency of expanded polystyrene (EPS), the cement-based composites filled with EPS beads can be regarded as a type of “porous” material. The electromagnetic reflection loss of this porous composite material in the frequency range from 8 to 18 GHz was studied experimentally in this paper. Findings show that the filling of EPS beads can improve the reflection loss of plain cement material greatly and the EPS filling ratio, EPS bead size and sample thickness all have remarkable effects on the electromagnetic wave reflection loss of this porous composite material. With a EPS filling volume concentration of 60% and EPS size of 1 mm, the reflection loss is all higher than −8 dB in 8–18 GHz and the bandwidth for −10 dB reaches 6.2 GHz for a sample with the thickness of 20 mm. This composite material still has a relatively low bulk density and can be handled easily.     

Open-cell cavity-integrated injection-molded acoustic polypropylene foams

In this study, a commercially available foam injection-molding machine was enhanced with a mold opening technique to produce polypropylene open-cell acoustic foams. Gas counter-pressure was used to improve the cell morphology and uniformity of the injection-molded foams. Their structure and thickness were controlled by applying different degrees of mold opening. The sample structure, the cell morphology, and the acoustic behavior of the foams were characterized. A foamed structure with an open-cell content of 67% and an expansion ratio of 4.6 was obtained when the mold was opened by 4.5 mm. Although further opening of the mold did not significantly increase the open-cell content, it triggered crack creation in the middle of the foams, where the creation of cavities was also facilitated. The injection-molded foams with a cavity and a high open-cell content, presented remarkable acoustic properties: a peak absorption coefficient of 0.95 was observed for foam with a 73% open-cell content and a 9 mm cavity. An automated system was also developed to perforate the acoustic foams, and the acoustic properties of foams both with and without perforation were studied. While perforating the foams widened their absorption coefficient frequency spectrum, it did not improve their transmission loss.     

Closed cell ZA27–SiC foam made through stir-casting technique

Closed cell zinc aluminum alloy (ZA27)–SiC composite foam has been synthesized using conventional stir-casting technique and CaH₂ as foaming agent. The synthesized foams are characterized in terms of its micro-architectural characteristics and deformation responses under compressive loading. It is observed that ZA27–SiC foams could be easily foamed without any difficulty. The density of the developed foam ranges from 0.25 gm/cc to 0.45 gm/cc due to the variation of CaH₂ percentage. The plateau stress and energy absorption of these foams follow power law relationship with relative density. Wherein, the densification strain follows a linear relationship with the relative density.     

Agrofibre reinforced poly(lactic acid) composites: Effect of moisture on degradation and mechanical properties

Natural fibre reinforced PLA composites are a 100% biobased material with a promising mechanical properties profile. However, natural fibres are hygroscopic whereas PLA is sensitive to hydrolytic degradation under melt processing conditions in the presence of small amounts of water. Here, we determine the effect of water content in undried and dried natural fibres on semi crystalline grade PLA degradation during processing as well as on the composite’s mechanical performance. The fibres evaluated are ramie, flax and cotton, containing 6–9 mass% moisture in the undried state and 0.2–0.4 mass% in the dried state. Intrinsic viscosity and melt flow index analysis indicate that the effect of the different levels of moisture in the fibres have a similar and small effect on PLA degradation, PLA hydrolysis appears rather affected by fibre diameter. Morphology, flexural strength and stiffness and Charpy impact of the composites are not significantly affected by the water present in the undried fibres.     

Mechanical properties of components fabricated with open-source 3-D printers under realistic environmental conditions

The recent development of the RepRap, an open-source self-replicating rapid prototyper, has made 3-D polymer-based printers readily available to the public at low costs ( < $500). The resultant uptake of 3-D printing technology enables for the first time mass-scale distributed digital manufacturing. RepRap variants currently fabricate objects primarily from acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA), which have melting temperatures low enough to use in melt extrusion outside of a dedicated facility, while high enough for prints to retain their shape at average use temperatures. In order for RepRap printed parts to be useful for engineering applications the mechanical properties of printed parts must be known. This study quantifies the basic tensile strength and elastic modulus of printed components using realistic environmental conditions for standard users of a selection of open-source 3-D printers. The results find average tensile strengths of 28.5 MPa for ABS and 56.6 MPa for PLA with average elastic moduli of 1807 MPa for ABS and 3368 MPa for PLA. It is clear from these results that parts printed from tuned, low-cost, open-source RepRap 3-D printers can be considered as mechanically functional in tensile applications as those from commercial vendors.     

Morphology,interfacial and mechanical properties of polylactide/poly(ethylene terephthalate glycol) blends compatibilized by polylactide-g-maleic anhydride

Polylactide/poly(ethylene terephthalate glycol) (PLA/PETG 80/20 wt) blends compatibilized with polylactide-g-maleic anhydride (PLA-g-MAH) were prepared by melt blending and the rheological, morphological and mechanical properties of the blends were studied. PLA/PETG (80/20 wt) blend formed a typical sea-island morphology, while upon compatibilization, the size and size distribution of the dispersed phase decreased significantly and the 3 wt% PLA-g-MAH compatibilized blend exhibited the smallest phase size and the narrowest distribution of the dispersed particles. The interfacial tension between PLA and PETG was determined from the morphological characteristics and the viscoelastic response of PLA/PETG blends via using two emulsion models. A minimum for PLA/PETG blend containing 3 wt% PLA-g-MAH was observed from both Palierne model and G–M model. The elongation-at-break increased by ∼320%, from 6.9% for PLA to 28.7% for the blend containing 3 wt% PLA-g-MAH without significant loss in the tensile modulus and tensile strength.     

Compositional variation of photoluminescence from Mn doped MgAl2O4 spinel

Spinel (MgAl₂O₄) crystals doped with 1.0% Mn have been grown by floating zone (FZ) technique with various Mg compositions, x = MgO/Al₂O₃, from 0.2 to 1.0. Compositional variations of photoluminescence are evaluated for a fluorescence thermometer application using crystals grown. Strong photoluminescence (PL) peak is observed at λ from 512 to 520 nm from the crystals grown from compositions, x, from 0.3 to 1.0. Peak wavelength of PL increases linearly from 512 to 520 nm with x. Weak PL peaking at λ = 750 nm is also observed from the specimens. Compositional variations of PL are considered to be due to the variation of crystal field surrounding the Mn²⁺ ions. The variation of crystal field strength agrees with the compositional variation of lattice constant.     

Preparation of low-density polyethylene/low-temperature expandable graphite composites with high thermal conductivity by an in situ expansion melt blending process

A facile strategy with the advantages of low cost and ease of mass production was presented to prepare low-density polyethylene (LDPE)/low-temperature expandable graphite (LTEG) composites with relatively high thermal conductivity by an in situ expansion melt blending process. LTEGs were expanded and delaminated into graphite multi-layers and graphite nanoplatelets during processing which synergistically created more thermo-conducting paths in the composites and hence led to great improvements in thermal conductivity. Thermal conductivity of the composite with 60 wt% of LTEG loading was increased by 23 times as compared to the pure LDPE, increasing from 0.47 to 11.28 W/mK. The incorporation of LTEG decreased the melting temperature and the degree of crystallinity of LDPE. Percolation threshold of both the electrical conductivity and rheological measurements was observed at about 8 vol% of LTEG loading. Moreover, the LDPE/LTEG composites showed better thermal stability compared to the pure LDPE.     

High temperature mechanical properties of low alloy steel foams produced by powder metallurgy

Cu–Ni–Mo and Mo based steel foams having different porosity levels for high temperature applications were produced by the space holder-water leaching technique in powder metallurgy. Steel powders were mixed with binder (polyvinylalcohol) and spacer (carbamide), and compacted. Spacer in the green compacts was removed by water leaching at room temperature and porous green compacts were sintered at 1200 °C for 60 min in hydrogen atmosphere. The successful application of foams at higher temperatures requires a good understanding of their high temperature mechanical properties. Compression tests were carried out on steel foams with different porosities at temperatures varying from room temperature to 600 °C in argon atmosphere. Effect of high temperature on compressive properties of the steel foams was investigated. It was found that the compressive strength of steel foams was greater at elevated temperatures than that at room temperature. This occurs across a range of temperatures up to 400 °C. Beyond this point the compressive strength decreased as the temperature increased. The reason for the enhancement of the compressive strength of Cu–Ni–Mo and Mo based steel foams is expected to be due to the effect of the dynamic age-hardening.     

Development of PLA/cellulosic fiber composite foams using injection molding: Crystallization and foaming behaviors

Poly(lactic acid) (PLA) and northern bleached softwood kraft (NBSK) or black spruce medium density fiberboard (MDF) fibers were melt compounded using a co-rotating twin screw extruder and subsequently microcellular injection molded. Poly(ethlylene glycol) (PEG) was used as a lubricant. The microcellular structure, thermal properties, and crystallization behaviors were characterized using scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and wide angle X-ray diffraction. Results show that cellulosic fibers, acting as crystal nucleating agents, increased the crystallization temperature and the crystallinity and decreased the crystallization half time. The dissolved N₂, the shear stress, and biaxial stretching during foaming also enhanced the crystallinity of PLA. Compared to PLA/PEG, a finer and more uniform cell structure was achieved in the cellulosic fiber composite foams. The improved foam morphology was attributed to the cell nucleating effects of the fibers and the increased melt strength by the addition of cellulosic fibers and by the gas- and fiber- induced crystallization.     

Influence of alkali treatment on the interfacial and physico-mechanical properties of industrial hemp fibre reinforced polylactic acid composites

The focus of this work was to produce short (random and aligned) and long (aligned) industrial hemp fibre reinforced polylactic acid (PLA) composites by compression moulding. Fibres were treated with alkali to improve bonding with PLA. The percentage crystallinity of PLA in composites was found to be higher than that for neat PLA and increased with alkali treatment of fibres which is believed to be due to the nucleating ability of the fibres. Interfacial shear strength (IFSS) results demonstrated that interfacial bonding was also increased by alkali treatment of fibres which also lead to improved composite mechanical properties. The best overall properties were achieved with 30 wt.% long aligned alkali treated fibre/PLA composites produced by film stacking technique leading to a tensile strength of 82.9 MPa, Young’s modulus of 10.9 GPa, flexural strength of 142.5 MPa, flexural modulus of 6.5 GPa, impact strength of 9 kJ/m², and a fracture toughness of 3 MPa m^1/2.     

Semisolid melt squeezing procedure for production of open-cell Al–Si foams

Melt squeezing process in semisolid state was used for the first time for production of open-cell Al–Si foams with improved microstructural and mechanical characteristics. First a given amount of preheated NaCl particles was stirred into molten A356 alloy. Stirring continued during solidification of the slurry until reaching a given solid fraction of primary particles. The resulting mixture was pressed by a perforated piston to squeeze a controlled amount of the residual meltout. Open-cell foams were achieved by leaching the final Al–Si–NaCl composites in water. The suitable values of the NaCl particle size, pressurizing temperature, melt to salt ratio and piston pressure for production of uniform and high integrity foams were obtained to be 3400 μm, 605 °C, 1.5:1 and 10 MPa, respectively. The results showed that the semisolid processing employed could refine and modify the microstructure of the cell ligaments in the final foams. Mechanical properties of the foams such as energy absorption and fracture toughness were also improved by the semisolid processing.     

聚丙烯发泡珠粒的结晶熔融行为与发泡特性

以CO_2为发泡剂,用高压釜式法制备了发泡聚丙烯(EPP)珠粒。采用差示扫描量热仪和扫描电子显微镜探讨了发泡温度(T_f)和发泡压力(p_f)对EPP结晶熔融行为和发泡特性的影响。结果表明,分别提高发泡温度或压力,EPP的熔融双峰均向高温方向移动,低温晶体与高温晶体的结晶度之比增大,而且温度对双峰的影响比压力更敏感。p_f在2~4 MPa内,EPP的发泡倍率和泡孔密度随p_f增大而增大;T_f在133.6~140℃间,发泡倍率和泡孔尺寸随T_f升高而变大,泡孔密度随T_f升高而变小。在T_f为133.6℃,pf为4 MPa时,EPP的熔融双峰结构比例合适,发泡倍率较大,泡孔密度最大且尺寸分布均匀、表面光滑。     

Fabrication and characterization of boron nitride bulk foam from borazine

Boron nitride (BN) ceramic bulk foams larger than 10 × 10 × 1 cm are fabricated by the pyrolysis of polyborazine foams that are prepared by fast curing of borazine. The principle of the self-foaming phenomenon is the emitting of H₂ in condensation polymerization during the curing of borazine. The as-fabricated BN ceramic foams exhibit closed cells with sizes ranging from 50 to 100 μm and controlled bulk densities varying from 0.08 to 0.25 g cm⁻³ depending on the different cured pressures. Studies on the microstructure and properties of the porous material show that the BN ceramic foams exhibit high specific strength, low dielectric constants and loss tangents, and good thermal conductivity. These characteristics make them useful for high temperature radomes and thermal insulation.     

Effects of specimen aspect ratio on the compressive properties of Mg alloy foam

Closed-cell AZ31 Mg alloy foams were successfully prepared by melt-foaming method. The effects of specimen aspect ratio (the thickness/width ratio, AR) on the compressive properties of closed-cell Mg alloy foams were investigated systematically. The results showed that the length of stress–strain plateau stage extended and ideality energy absorption efficiency improved with the specimen AR increasing and the yield strength decreased. Specimens with the AR = 1.00 possess good combination of yield strength, plateau stage length and compressive stability when compressed under the experiment conditions.     

Laser surface melting of a complex high alloy steel

The effect of laser surface melting (LSM) on the microscopic morphology of a complex high alloy steel has been examined in single track experiments. Different combinations of power (1–4 kW) and scan speed (500–1000 mm min⁻¹) were selected in order to obtain a range of depths of melt penetration. An increase in the depth of melt penetration has correlated with rise in the estimated surface temperature induced by laser melting. Within the strongly refined structure of the laser melted alloy, the interdendritic spacing, λ varied from 0.29 μm to 0.97 μm with increase in the depth of melt penetration. The microhardness in the laser surface melted region has been shown to decrease linearly with λ^−0.5.     

Passive mode-locking performance comparison between composite and single Nd:YVO4 crystals

The mode-locked performances of composite and conventional Nd:YVO₄ crystals were demonstrated with a semiconductor saturable absorber mirror. For the conventional crystal, power saturation was observed when the pump power exceeded 5.31 W, while for the composite crystals, the output power increased linearly with the pump power, showing good thermo-mechanical performances. The maximum average output power of 1.2 W was achieved by a composite crystal at an incident pump power of 7.09 W. The largest pulse energy of 34.6 nJ and the highest peak power of 4.9 kW with a pulse duration of 7 ps were also obtained by the same composite crystal while the non-composite crystal got the shortest pulse duration of 5.3 ps. The theoretical analysis on pulse duration for different laser media is in agreement with the experimental result.