General Purpose Polystyrene Research Articles

Styrene Migration from Polystyrene for Food Contact: A Case Study on the Processing Chain of Yoghurt Pots

A precautionary specific migration limit of 40 µg/kg for styrene from food contact materials is currently under evaluation in Europe. In the ongoing discussion about applicable methods to demonstrate compliance, testing with food instead of simulants or total transfer calculations has been proposed. In this study, the residual styrene levels in high-impact polystyrene (HIPS) blended with general-purpose polystyrene (GPPS) were determined at several levels of the processing chain of yoghurt pots (from pellets to sheets, then to pots). The styrene migration from extruded sheets and thermoformed pots was analyzed in food simulants at 10 days/20 °C and 40 °C, as well as in yoghurt after storage at 8 °C after 50 days. The obtained results show that the residual styrene content in the PS materials correlates with migration. However, the migration of styrene was far below the total transfer assumption. Styrene migration from the sheets into food simulants and into yoghurt exceeded that migrating from the pots. Styrene migration into food simulants in 20% ethanol at 10 days/20 °C and 40 °C and, more clearly, in 50% ethanol at 10 days/40 °C, was higher than that into yoghurt tested on the best-before date. Styrene migration from PS pots into yoghurt after storage at 8 °C for 50 days reached up to 15 µg/kg (applying the EU cube model), which would be conservatively covered by testing the PS pots with 20% ethanol at 10 days/20 °C.

Removal of undissolved substances in the dissolution-based recycling of polystyrene waste by applying filtration and centrifugation

Polystyrene (PS) is a versatile polymer typically used in applications such as yogurt cups, packaging trays, disk cases and toys. To increase recycling rates of PS, dissolution recycling is being investigated, which involves the liquefication of the polymer in a suitable solvent, allowing deep cleaning of the polymer from impurities. Quite specific to PS is that polystyrene waste contains both general-purpose polystyrene and high-impact polystyrene (HIPS), which is composed of free PS and polystyrene-grafted polybutadiene particles. In this work the potential of filtration and centrifugation is analyzed with the aim of cleaning the polymer from both, insoluble PB-PS particles and pigments (TiO2, Cr/Sb/Ti oxide and carbon black). The dead-end lab scale filtration were performed at room temperature and at pressures between 1.5 and 30 bar. The pigments were successfully removed, yet, filtration of HIPS solutions results in low fluxes due to extreme membrane fouling caused by the PB-PS particles, which was confirmed by the application of pore-blockage filtration models. Alternatively, centrifugation at 14,052 G-force has shown to be a promising alternative to separate the particles from HIPS, resulting in 100% turbidity reduction. Equally, the separation of pigments was successful, highlighting that TiO2 and Cr/Sb/Ti oxide have shorter sedimentation times compared to carbon black. Finally, the two separation processes are tested on a PS rigid packaging waste sample coming from a sorting line and the results show that centrifugation allows a high turbidity reduction and that a two-step separation process starting with centrifugation for PB-PS particles removal can facilitate further downstream cleaning.

Flame Retardant Nanocomposites of Polystyrene-Modified Sepiolite Clay

Flame retardancy is the property that is highly demanded when it comes to deal with plastics in different industries. In this research general purpose polystyrene (GPPS) and modified sepiolite clay are melt blended together to fabricate flame retardant nanocomposites. Structural analysis were performed with the help of Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) techniques. Morphological analysis of the fabricated nanocomposites were carried out using scanning electron microscope (SEM). As a result of better clay dispersion in polymer matrix and intermolecular interactions, mechanical properties are also improved. The standard procedure (ASTM D4986-20) was followed for observing the flame retardancy of the fabricated nanocomposites. Tangible decrease is noted upto 48% in burning rate of the optimum sample which reflects improvement in flame retardancy.

Film-trigger applicator (FTA) for improved skin penetration of microneedle using punching force of carboxymethyl cellulose film acting as a microneedle applicator

BackgroundDissolving microneedle (DMN) is a transdermal drug delivery system that creates pore in the skin and directly deliver drug through the pore channel. DMN is considered as one of the promising system alternatives to injection because it is minimally invasive and free from needle-related issues. However, traditional DMN patch system has limitations of incomplete insertion and need of complex external devices. Here, we designed film-trigger applicator (FTA) system that successfully delivered DMN inside the skin layers using fracture energy of carboxymethyl cellulose (CMC) film via micropillars. We highlighted advantages of FTA system in DMN delivery compared with DMN patch, including that the film itself can act as DMN applicator.MethodsFTA system consists of DMNs fabricated on the CMC film, DMN array holder having holes aligned to DMN array, and micropillars prepared using general purpose polystyrene. We analyzed punching force on the film by micropillars until the film puncture point at different CMC film concentrations and micropillar diameters. We also compared drug delivery efficiency using rhodamine B fluorescence diffusion and skin penetration using optical coherence tomography (OCT) of FTA with those of conventional DMN patch. In vivo experiments were conducted to evaluate DMN delivery efficiency using C57BL/6 mice and insulin as a model drug.ResultsFTA system showed enhanced delivery efficiency compared with that of the existing DMN patch system. We concluded CMC film as a successful DMN applicator as it showed enhanced DMN penetration in OCT and rhodamine B diffusion studies. Further, we applied FTA on shaved mouse dorsal skin and observed successful skin penetration. The FTA group showed higher level of plasma insulin in vivo than that of the DMN patch group.ConclusionsFTA system consisting of simple polymer film and micropillars showed enhanced DMN delivery than that of the existing DMN patch system. Because FTA works with simple finger force without sticky patch and external devices, FTA is a novel and promising platform to overcome the limitations of conventional microneedle patch delivery system; we suggest FTA as a next generation applicator for microneedle application in the future.

Review on valorization of lignocellulosic biomass for green plastics production: Sustainable and cleaner approaches

Environmental problems associated with world's largest energy source namely fossil fuels are well known. In addition, petroleum and other nonrenewable energy sources are running out and will be depleted soon. However, many polymers are derived from petroleum. In the face of international movement away from oil-based polymers such as, general purpose polystyrene, polypropylene, polyethylene, terephthalate, high density and low density polyethylene, polycarbonate, polyvinyl chloride, and towards a safe and sustainable future, major research labs in the world are trying to uncover the big breakthrough, particularly via utilizing natural/renewable agro-residues as a substrate for green biopolymers. Considering, non-edible lignocellulosic biomass (LCB) as a feedstock for bio-polymers production as it does not interfere with food security, generate no tailpipe emissions, and also lead to reduction in stubble burning. Among possible organic sources of biopolymers, micro- and macro- algae, provides a wide variety of proteins, lipids, polyphenols, and polysachharides which are currently employed for pharmaceutical, packaging, food, and biomedical applications. Current review summarizes the key insights on microbial biopolymer production from LCB and algal biomass by means of circular bioeconomy. Biobased approach will not only reduce the process cost but also generates economy for farmers globally and promotes innovation in domestic manufacturing.

Morpho-structural and thermo-mechanical characterization of recycled polypropylene and polystyrene from mixed post-consumer plastic waste

In this work, a complete sorting and characterization of dirty non-recyclable mixed plastic (plasmix fraction) from municipal solid waste was performed. The procedure comprised a visual inspection and identification of the materials presented in the mixed plastic bales, and subsequent moisture and dirt content determination. Afterwards, both polypropylene and polystyrene fractions obtained from the sorting process were recycled and physico-mechanically and thermally characterized for the assessment of recycled material quality. The dirty non-recyclable mixed plastic from municipal solid waste was composed of polypropylene (28.89 %), polyethylene terephthalate (22.02 %), polystyrene (9.65 %) and rigid polyethylene (4.68 %). Regarding the moisture and dirt content of the mixed plastic fraction, the results were highly variable, mainly due to the heterogeneity of the material, its origin, atmospheric conditions, etc. The average sum of both parameters (moisture and dirt) was around 15 %. The mechanical properties were within the expected range for each type of polymer, noting that polystyrene recycled materials are more brittle than recycled polypropylene. The recycling of non-food polypropylene wastes yielded a material with higher impact resistance (70 kJ m−2) and Young´s modulus (1934 MPa) as compared to that obtained from the recycling of food packages. Concerning the polystyrene recyclates, it is worth mentioning that recycled materials obtained from foamed residues (expanded polystyrene and extruded polystyrene showed approximately twice the tensile strength with respect to the recycled materials from high impact polystyrene and general-purpose polystyrene residues. In some cases, infrared and thermal analyses revealed cross-contamination with traces of other polymers.

Migration Testing of GPPS and HIPS Polymers: Swelling Effect Caused by Food Simulants Compared to Real Foods.

Migration kinetic data from general purpose polystyrene (GPPS) and high impact polystyrene (HIPS) were generated for a set of model substances as well as styrene monomer and oligomers at different temperatures (20 °C, 40 °C, 60 °C) using food simulants stipulated in the European Regulation (EU) 10/2011 and real foods like milk, cream and olive oil (20 °C, 40 °C). The extent of polymer swelling was characterized gravimetrically and visual changes of the test specimens after migration contact were recorded. Isooctane and 95% ethanol caused strong swelling and visual changes of HIPS, overestimating real migration into foods especially at high temperatures; GPPS was affected by isooctane only at 60 °C. With 50% ethanol, after 10 days contact at 60 °C or 40 °C both polymers were slightly swollen. Contrary, most of the real foods analyzed caused no detectable swelling or visual changes of the investigated polymers. This study demonstrates that the recommendations provided by EU regulations are not always in agreement with the physicochemical properties of styrenic polymers. The critical point remains the selection of adequate food simulants/testing conditions, since the high overestimation of aggressive media can lead to non-compliance of polystyrene materials even if the migration into real food would be of no concern.

Phase morphology and thermomechanical performance of thermoplastic corn starch/polystyrene blends

This study compared the preparation and characterization of polymer blends containing two types of polystyrene (high-impact polystyrene (HIPS) and general-purpose polystyrene (GPPS)) and thermoplastic corn starch (TPS) as a natural resource. Melt extrusion was used to create TPS/polystyrene blends. SEM, XRD, and DMTA analyses were used to determine the compatibility and mechanical properties of GPPS/TPS and HIPS/TPS blends. SEM analysis revealed that TPS particle size was significantly smaller in HIPS blends than in GPPS blends, owing to lower interfacial tension and better compatibility between HIPS and TPS. According to the DMTA results, the storage modulus of both blends increased significantly, particularly at high PS concentrations. All blends had two peaks on the loss factor curve, one for each phase's glass transition. The Tg of the PS-rich phase in blends was nearly equivalent to the Tg of pure PS. On the other hand, Tg of the TPS-rich phase was unexpectedly lower than that of pure TPS. By adding a low volume of polystyrene to TPS (approximately 20 wt%), the ultimate tensile strength of TPS was increased by more than 200%. At high polystyrene concentrations (approximately 80 wt%), the blend exhibited mechanical properties comparable to pure PS.

Techno-economic risk assessment, life cycle analysis and life cycle costing for poly(butylene succinate) and poly(lactic acid) production using renewable resources

The sustainable production of poly(lactic acid) (PLA) or poly(butylene succinate) (PBS) from corn glucose syrup, corn stover and sugar beet pulp (SBP) have been assessed via process design, preliminary techno-economic evaluation, life cycle assessment and life cycle costing (LCC). Cost-competitive PLA and PBS production can be achieved in a SBP-based biorefinery, including separation of crude pectin-rich extract as co-product, leading to minimum selling prices of $1.14/kgPLA and $1.37/kgPBS. Acidification Potential, Eutrophication Potential and Human Toxicity Potential are lower when SBP is used. The LCC of PLA ($1.42/kgPLA) and PBS ($1.72/kgPBS) production from SBP are lower than biaxial oriented polypropylene (BOPP, $1.66/kg) and general purpose polystyrene (GPPS, $2.04/kg) at pectin-rich extract market prices of $3/kg and $4/kg, respectively. Techno-economic risk assessment via Monte-Carlo simulations showed that PLA and PBS could be produced from SBP at the market prices of BOPP ($1.4/kg) and GPPS ($1.72/kg) with 100% probability to achieve a positive Net Present Value at pectin-rich extract market prices of $3/kg and $4/kg, respectively. This study demonstrated that SBP-based biorefinery development ensures sustainable production of PLA and PBS as compared to fossil-derived counterparts and single product bioprocesses using glucose syrup and corn stover.

Influences of different source microplastics with different particle sizes and application rates on soil properties and growth of Chinese cabbage (Brassica chinensis L.)

The potentially negative effects of microplastics (MP) on agroecosystems have raised worldwide concerns. However, little is known about the negative effects of MP exposure on the soil–plant system. To fill up this knowledge gap, a pot experiment was set up, and two different MP types [high density polyethylene (HDPE) and general purpose polystyrene (GPPS)] were used, which had four particle sizes (<25, 25–48, 48–150, and 150–850 µm) at four application rates (2.5, 5, 10, and 20 g MP kg−1 soil). Some soil properties and the growth of Chinese cabbage (Brassica chinensis L.) were monitored. The results showed that (1) MP application with high application rates and relatively small particle sizes significantly enhanced the soil urease activity, which accompanied with enhanced soil pH and decreased soil available concentrations of phosphorus and potassium in some cases. (2) The exposure of MP did not significantly affect the activity of soil catalase regardless of their application rates and sizes. MP with different application rates and small sizes significantly reduced the soil sucrase activity, but the largest size of MP enhanced the activity of soil sucrase. (3) GPPS at 10–20 g kg−1 or with the sizes of <25 and 48–150 µm significantly reduced the fresh weight of Chinese cabbage, but the addition of HDPE had no remarkable effects on the fresh weight regarding of its application rates or sizes. (4) MP with high application rates and large sizes enhanced but small sizes of MP reduced the leaf soluble sugar concentration. The increasing application rates of MP and small size HDPE significantly reduced the starch concentration in the leaves of Chinese cabbage, however, the different sizes of GPPS showed limited effects on the leaf starch. The addition of MP with increasing application rates and different sizes always reduced the concentration of leaf chlorophyll. These parameters regarding to plant and soil could be used to assess the risks of MP pollution in the soil–plant systems. We found that the risks resulting from MP pollution were MP type-dependent and particle size-dependent. These findings indicate that overaccumulation of MP in the agriculture may possess an ecology risk and will negatively affect the agricultural sustainability and the food safety.

Extension of the Equivalent Material Concept to Compressive Loading: Combination with LEFM Criteria for Fracture Prediction of Keyhole Notched Polymeric Samples

This work analyzes, both theoretically and experimentally, the fracture process of square specimens weakened by keyhole notches and subjected to compressive stresses. Two materials are covered: general-purpose polystyrene (GPPS) and poly(methyl methacrylate) (PMMA). Firstly, the load-carrying capacity (LCC) of the specimens is determined experimentally. Then, by using the equivalent material concept (EMC) for compressive conditions coupled with the maximum tangential stress (MTS) and the mean stress (MS) criteria, the LCC of the notched specimens is predicted. The results show that by using the approach proposed in the present investigation, not only can the critical loads in the keyhole notched polymeric specimens be precisely predicted, but also the corresponding compressive critical stress of the two mentioned polymers can be successfully estimated.

Diffusion Coefficients and Activation Energies of Diffusion of Organic Molecules in Polystyrene below and above Glass Transition Temperature.

General Purpose Polystyrene (GPPS) and High Impact Polystyrene (HIPS) is used in packaging food as well as for technical products. Knowledge of the diffusion behavior of organic molecules in polystyrene (PS) is important for the evaluation of the diffusion and migration process. Within this study, diffusion coefficients were determined in GPPS and HIPS below and above the glass transition temperature. Diffusion coefficients were determined from desorption kinetics into the gas phase using spiked GPPS and HIPS sheets as well as from permeation kinetics through a thin GPPS film. Overall, 187 diffusion coefficients were determined in GPPS and HIPS at temperatures between 0 °C and 115 °C. From the temperature dependency of the diffusion coefficients 45 activation energies of diffusion EA and the pre-exponential factor D0 were determined. As expected, the activation energies of diffusion EA show a strong dependency from the molecular volume of the investigated substances. At the glass transition temperature, only a slight change of the diffusion behavior were observed. Based on EA and D0, prediction parameters for diffusion coefficients were established.

Sulfenamides as Standalone Flame Retardants for Polystyrene

Efficient standalone sulfenamide based flame retardants consisting of N-benzothiazol-2-ylsulfanyl-N-tert-butyl-benzothiazole-2-sulfenamide (SF-201) or N-cyclohexylthiophthal-imide (SF-205) have been developed for bulk and expanded polystyrene (EPS). In the first set of experiments the sulfenamides were mixed with general purpose polystyrene (GPPS) in a Haake Rheocord melt blender, and in the second set of experiments suspension polymerizations of styrene were carried out in the presence of either of the sulfenamides. Under these experimental conditions SF-201 was deemed to be a more effective flame retardant than SF-205. The third set of experiments involved all the relevant steps for industrial production of EPS: Preparation of polystyrene beads containing pentane as blowing agent and SF-201 as the sole flame retardant, subsequent pre-expansion of the beads at 120 °C with steam and in the last step molding with steam to produce large EPS blocks. The prepared EPS blocks were cut into desired dimensions for EN ISO 11925-2 fire tests. The obtained beads containing SF-201 had a spherical shape and their particle size distribution as well as molecular weights were rather similar to the reference polystyrene beads. Thus, it seems that SF-201 did not have a notably negative influence in the process of breakage and coalescence of monomer/polymer droplets. In addition, the molecular weight distribution remained narrow and a slight decrease in polystyrene molecular weights were observed in comparison to neat polystyrene prepared under similar conditions. The flame retardant efficacy of SF-201 as a standalone flame retardant in EPS was high, as at 2.5 % loading of SF-201 in EN ISO 11925-2 ignitability test the EN 13501-1 E class with no flammable droplets was obtained. The thermogravimetric analysis (TGA) carried out under inert atmosphere revealed enhanced and earlier onset of polystyrene degradation in the presence of sulfenamides. The enhanced polystyrene degradation led to a lowering of melt viscosity that facilitated an effective mass transfer of fuel and heat away from the fire zone. The pyrolysis gas chromatography-mass spectrometry (PyGCMS) measurements of blends showed a lower level and number of polystyrene related degradation products (styrene, multiple dimer and trimer species) and evidence of parent SF-201 flame retardant molecule was no longer visible. Whereas new volatile amine species such as tert-butylamine and N-tert-butyl-2-benzothiazolesulfenamide were detected which relate to flame retardant activity in the condensed phase and potentially radical scavenging of key combustion radicals (H., .OH) in gas-phase.

A New Composition of High Heat General Purpose Polystyrene (High Heat GPPS) Resin

Academic Journal of Polymer science (AJOP) is a Journal which publishes state-of-the-art overview articles by internationally recognized authorities in polymer science and engineering. It covers all the areas of particular interest are biomedical applications,

Notch Fracture in Polymeric Specimens under Compressive Stresses: The Role of the Equivalent Material Concept in Estimating the Critical Stress of Polymers

In this paper, the fracture of notched polymeric specimens under compressive stresses was investigated both experimentally and theoretically. In the experimental section, to determine the load-carrying capacity (LCC) of U-notched specimens made of general-purpose polystyrene (GPPS) and polymethyl-methacrylate (PMMA) polymers, tests were performed on notched square samples under compression, i.e., negative mode I loading. In the observation of the nonlinear behavior of the two polymers in the standard compressive tests, for the first time, the equivalent material concept (EMC) was used under compressive loading to theoretically estimate the critical stresses of the two polymers, which were shown to be significantly different from the ultimate strengths obtained from the standard compression tests. By linking the EMC to the maximum tangential stress (MTS) and mean stress (MS) criteria, the LCC of the notched specimens was predicted. The outcomes are twofold: First, MTS, MS, EMC–MTS, and EMC–MS criteria provide accurate predictions of the experimental critical loads observed in the U-notched polymeric specimens; second, the combination of the EMC with the MTS and MS criteria, allow such predictions to be obtained without any need for experimental calibration.

Pyrolysis-catalysis of different waste plastics over Fe/Al2O3 catalyst: High-value hydrogen, liquid fuels, carbon nanotubes and possible reaction mechanisms

To understand the correlation between plastic structure and products, and the possible reaction mechanisms, the pyrolysis–catalysis of different types of waste plastics was investigated in the presence of an Fe/Al2O3 catalyst. Polypropylene (PP), high-density polyethylene (HDPE), low-density polyethylene (LDPE), high-impact polystyrene (HIPS), and general-purpose polystyrene (GPPS) were used as the feedstock. The results showed that PP, HDPE, and LDPE showed higher H2-enriched gaseous product yields (>40 wt%), but higher H2 concentration (over 70 vol%) was obtained from the gaseous products of HIPS and GPPS. In terms of liquid oil, the yield exhibited a relatively stable tendency, which was ~ 20 wt%, and the liquid product comprised hydrocarbons with a carbon number range mainly between 8 and 16. For solid carbon deposits, HIPS waste plastic led to a higher solid deposit yield of 49.4 wt%, followed by GPPS of 48.7 wt%. By contrast, PP, HDPE, and LDPE showed lower yields of 30.2 wt%, 36.9 wt%, and 35.9 wt%, respectively. In summary, more, purer and cleaner carbon nanotubes (CNTs) could be obtained from pyrolysis–catalysis of polyolefin (PP and PE), while more amorphous carbon and hydrogen were gathered from PS.

Studying the Influence of the Mixing Speed of the Polymer Blend of General-Purpose Polystyrene and Acrylonitrile-Butadiene Styrene with the Applications of Artificial Neural Networks

General Purpose Polystyrene (GPPS) has weak properties and this weakness made the applications of this polymer be limited. Therefore, the use of the mixtures of polymers can improve these properties. Different parameters like the mixing speed can affect the quality of the properties of preparing polymer from the mixture of several polymers. In this research, the polymer blend of GPPS and Acrylonitrile-Butadiene Styrene (ABS) has been investigated. In order to prepare this polymer mixture, GPPS has been considered as the main phase (base polymer) and ABS has been considered as the scattered phase (additive). Firstly, the blended polymers with different weight percentages (0, 0.04, 0.08 and 0.12) of ABS/GPPS in different mixing speeds (30, 40, 50 and 60 rpm) have been prepared and for each mixture, the Melt Flow Index (C), Vicat Softening Temperature, Tensile at Break and impact test have been measured. The laboratory data collected from different tests, has been simulated by the Multi-Layer Perceptron (MLP) method of Artificial Neural Networks (ANN) and the results of the simulated data covered the laboratory data perfectly. The results declare that the presence of ABS in the mixed polymer improved the Tensile strength and thermal properties. In order to reach the highest quality in carried out tests, it is considered to use ABS in a high percentage (0.12) and the maximum possible mixing speed (60 rpm).

Synthesis of polymer nanoparticles based highly selective membranes by mini-emulsion polymerization for dehydration of 1,4 dioxane and recovery of ethanol from water by pervaporation

Inorganic metal oxide or metal nanoparticles and organic graphene or carbon nanotube significantly improves the separation characteristics of polymer membranes. The high cost and compatibility issue of these nanoparticles may be countered by using low cost polymer nanoparticles (PNPs). Accordingly, several chitosan (CS) coated polyacrylonitrile (PAN) nanoparticles (CSPAN) were prepared by mini emulsion polymerization of acrylonitrile in the presence of chitosan as co-stabilizer. These CSPAN polymer nanoparticles were incorporated into polyvinyl alcohol (PVA). The filled PVA membrane was then crosslinked with maleic acid. The unfilled and filled PVA membranes were used for sorption and pervaporation of 1, 4-dioxane. Similarly, unfilled and CSPAN filled general purpose polystyrene (GPPS) membranes were used for recovery of ethanol from water. The structure, size, crystallinity, stability and morphologies of the PNPs and PNPs filled PVA and GPPS membranes were characterized with FTIR, NMR, SEM, TEM, EDAX and mechanical properties. The filled PVA18/GPPS3 membranes prepared with 18/3 wt% of CSPANs(of total PVA/GPPS wt.) containing 4.2/2.4 wt% of CS in CSPAN in PVA18/GPPS3 showed the best results for flux and selectivity (165.2/269.6 kg/m2h and 40.1/29.6 for PVA18/GPPS3) for azeotropic dioxane-water mixture (81.6 wt% dioxane) and 10 wt% ethanol in water. PVA18 and GPPS3 filled membranes were further used at varied feed concentrations of the organics in water. Both sorption and permeation were analyzed in terms of solvent-solvent and solvent-membrane interaction and solvent coupling. The hydrophilic filled PVA18 membranes showed high flux and water selectivity while the organophilic filled GPPS3 membranes showed high flux and ethanol selectivity.

Sorption Behaviors of Copper Ions and Tetracycline on Microplastics in Aqueous Solution

The interaction between microplastics, heavy metals, and antibiotics can lead to combined pollution, which could result in greater environmental damage. The pathway and mechanism of the interaction between microplastics, heavy metals, and antibiotics are the preconditions for evaluating the associated environmental risk; however, these are not well understood. As probe sorbates, the sorption behaviors of copper ions (Cu2+) and tetracycline (TC) on two microplastics [high density polyethylene (HPDE) and general-purpose polystyrene (GPPS)] in aqueous solution were investigated and the welding theory with relevant experimental results were discussed. The adsorption capacity of HDPE was greater than that of GPPS in a single Cu solution, whereas the reverse situation occurred in a single TC solution. Moreover, the adsorption capacity of the microplastics in a Cu2+-TC binary solution was larger than that in the single solutions. The pseudo-second-order kinetic models to describe the adsorption process were reasonable and the entire process could be divided into two phases:surface adsorption and internal diffusion. The Langmuir model provided a better fit of the data than did the Freundlich model. In the single solutions, the saturated adsorption amounts of Cu2+ and TC were 0.178 μmol·g-1 and 0.257 μmol·g-1, respectively, for GPPS, and 0.334 μmol·g-1 and 0.194 μmol·g-1, respectively, for HDPE. In the binary solution, the corresponding numerical values were 0.529 μmol·g-1 and 0.411 μmol·g-1, respectively, for GPPS and 0.471 μmol·g-1 and 0.341 μmol·g-1, respectively, for HDPE. The variations in the surface morphological characteristics and chemical functional groups were the main reasons for the difference in the adsorption behavior of microplastics. The variation of the pH of the adsorption system could change the existing forms and surface electrical properties of microplastics and adsorbed objects, and subsequently affected the equilibrium adsorption capacity. When the ambient temperature was in the range of 15 to 35℃, increasing the temperature was unfavorable for the adsorption process. Cu2+ and TC could produce a synergistic effect under the conditions of coexistence. The formation of complexes and bridging make Cu2+ and TC more easily adsorbed by microplastics.

Response surface method to study the effect of conical surface and vortex-finder lengths on de-foulant hydrocyclone with reflux ejector

The structure of the hydrocyclone always changes with the application scene due to its excellent separation performance. A de-foulant hydrocyclone with a reflux ejector (DFHRE) has a completely different flow field structure from that of a conventional one. Under the effect of the reflux ejector, DFHRE has the function of overflow-suck-underflow to achieve continuous discharge and high separation performance. To further improve its separation performance, an inner conical surface was added to control the turbulence intensity, and the suction angle and vortex-finder insertion depth were adjusted to control the intensity of the overflow-suck-underflow. The single factor method and response surface method (RSM) were used to conduct experiments through general-purpose polystyrene particles (GPPS) water and sewage. The results show that the separation performance of DFHRE first increased and then decreased as the lengths of conical surface Lc and vortex-finder Lv increase, whereas the separation efficiency and the energy consumption changed monotonically with the increase of suction angle α. For the results of RSM, these three factors (Lc, α, Lv) had significant effects on maximizing separation efficiency and minimizing split ratio, whereas their combined effects were not significant. Finally, the maximum separation efficiency and minimum total pressure drop optimized by the RSM model are 94.62% and 1.09 kPa, respectively. The optimal values of Lc, α, and Lv was 0.29 (height ratio of inner conical surface to that of the outer cone), 30°, and 0.50 (length ratio of the vortex-finder insertion to the total of cylinder-cone), respectively. Therefore, these three factors must be fully considered for designing DFHRE, and the insertion depth of the vortex-finder can exceed the interface of the cylinder and cone but not too much, which is different from that of the traditional hydrocyclone.