Effects of additives on PVC plastics surface and the natural flotability

Aging and characterization of disposable polypropylene plastic cups based microplastics and its adsorption for methylene blue

Microplastics (MPs) as emerging pollutants are of increasing concern, due to their ubiquitous, uncertain, and complex environmental impacts. Different from the standard spherical MPs without additives, here polypropylene microplastics (PP-MPs) in flake derived from the disposable plastic cup in food-grade in daily life were studied. The characterization of PP-MPs demonstrated that the carbonyl index represented the aging degree was enhanced from 0.26 significantly to 0.82 after 10 days, and the aging process fitted well with pseudo-first-order kinetic. Moreover, the crystallinity degree, polarity and surface negative charges were enhanced, while the hydrophobicity was decreased. The adsorption behavior of PP-MPs toward methylene blue (MB), and the impacts of various pHs, salinities, and humic acid in aquatic environments were also explored. The pseudo-second-order kinetic, Henry and Sips isotherm models provided a good correlation with the experimental data, indicating that the rate-limiting step was closely related with the complex surface adsorption, and the hydrophobic partitioning, polar interaction, electrostatic attraction, and hydrogen bonding were possibly involved in the adsorption. These exhaustive experiments aim to provide a theoretical basis for assessing and better understanding the environmental behavior of disposable PP plastic cups in nature.

Release of microplastics from typical rainwater facilities during aging process

As the demand for urban flood prevention and drainage increases, a large number of plastic rainwater facilities are in use. Microplastics will be released inevitably into stormwater systems during aging and hydraulic scouring processes, which could cause potential pollution risk. This study simulated the release behavior of microplastics from three typical plastic rainwater facilities including a rainwater inspection well, rainwater storage module, and rainwater pipe (mainly composed of high-density polyethylene, polypropylene, and polyvinyl chloride, respectively) under the effects of aging and hydraulic scouring. After 15-45 days of UV aging and 72 h of hydraulic scouring, the surfaces of the three facilities were found to exhibit increases in roughness, cracks, folds, and cavities, with the most pronounced changes occurring in the rainwater storage module. As the aging time increased, oxygen-containing functional groups formed and led to carbon chain scission. Fourier transform infrared spectroscopy (FTIR), two-dimensional correlation spectroscopy (2D-COS) and X-ray photoelectron spectroscopy (XPS) of facility surfaces showed that the formation of oxygen-containing functional groups was an important factor affecting the release of microplastics. The amount of microplastics released from the three facilities ranged from 160 to 1905 items/g (microplastics/facilities), following in the order of rainwater inspection well > rainwater storage module > rainwater pipe. The particle size of the released microplastics ranged from 3 to 1363 μm, with 10-30 μm accounting for the greatest proportion of particles, 50.10%. The size of microplastics released from the rainwater inspection well and rainwater storage module increased with the aging degree, while the release from the rainwater pipe decreased. The release behavior depends mainly on the composition of the materials and the aging time. Thus, microplastics can be released from plastic rainwater facilities under suitable conditions. The results can be used to further evaluate microplastic pollution caused by urban rainwater facilities.

A clean and efficient flotation towards recovery of hazardous polyvinyl chloride and polycarbonate microplastics through selective aluminum coating: Process, mechanism, and optimization

Polyvinyl chloride (PVC) and polycarbonate (PC) microplastics are major sources of hazardous chlorine and bisphenol A, threatening the ecosystem and environment. Plastic recycling can control the source of microplastics pollution, but the recycling of PVC and PC will be prevented by invalid separation. We established a novel and clean flotation method to separate PVC and PC microplastics by using aluminum coating. Trace amounts of Al(OH)₃ can selectively coat the PVC microplastics surface due to its strong affinity for PVC. The contact angle of PVC decreases by 24° due to abundant hydroxyl groups of Al(OH)₃ coating, whereas PC remained hydrophobic. Response surface methodology (RSM) combining Box-Behnken design (BBD) is used to optimize modification. A quadratic model is established to predict PC purity, explore the interaction between pH, aluminum chloride concentration, and ultrasonic duration. The recovery and purity of microplastics can exceed 99.65% with parameter optimization. The effects of multi-component, brand, shape, size, and mass ratio of plastics are utilized to evaluate the application potential. The suitable situations and limits of this method are disclosed. The aluminum coating offers significant benefits over other modifications in terms of reaction temperature, treatment time, and pollution prevention. Flotation based on aluminum coating provides a new insight for separating and recycling microplastics.

Understanding the fragmentation of microplastics into nano-plastics and removal of nano/microplastics from wastewater using membrane, air flotation and nano-ferrofluid processes

Nano/microplastics (NPs/MPs), a tiny particle of plastic pollution, are known as one of the most important environmental threats to marine ecosystems. Wastewater treatment plants can act as entrance routes for NPs/MPs to the aquatic environment as they breakdown of larger fragments of the plastic component during the treatment process; therefore, it is necessary to remove NPs/MPs during the wastewater treatment process. In this study, understanding the effect of water shear force on the fragmentation of larger size MPs into smaller MPs and NPs and their removal by air flotation and nano-ferrofluid (i.e., magnetite and cobalt ferrite particle as a coagulant) and membrane processes were investigated as a proof-of-concept study. It is found that a two-blade mechanical impeller could fragment MPs from 75, 150 and 300 μm into mean size NPs/MPs of 0.74, 1.14 and 1.88 μm, respectively. Results showed that the maximum removal efficiency of polyethylene, polyvinyl chloride and polyester was 85, 82 and 69%, respectively, in the air flotation process. Increasing the dose of behentrimonium chloride surfactant from 2 to 10 mg/L improved the efficiency of the air flotation process for NPs/MPs removal. It is also found that the removal efficiency of NPs/MPs by the air flotation system depends on solution pH, size, and types of NPs/MPs. This study also found a less significant removal efficiency of NPs/MPs by both types of ferrofluid used in this study with an average removal of 43% for magnetite and 55% for cobalt ferrite. All three plastics tested had similar removal efficiency by the nano-ferrofluid particles, meaning that this removal technique does not rely on the plastic component type. Among all the process tested, both ultrafiltration and microfiltration membrane processes were highly effective, removing more than 90% of NPs/MPs fragment particles. Overall, this study has confirmed the effectiveness of using air flotation and the membrane process to remove NPs/MPs from wastewater.

Microplastic abundance and characteristics in French Atlantic coastal sediments using a new extraction method

The ubiquitous presence of microplastics (MPs) has been demonstrated in all environmental compartments in the recent years. They are detected in air, freshwater, soil, organisms and particularly in marine ecosystems. Since sediments are known to be the major sink of many organic and inorganic pollutants, the aim of this study was to develop and validate a fast and cheap methodology to assess the MP contamination in intertidal sediments from the Gulf of Biscay (Pays de la Loire region, France). Sediments were sampled at three locations (Pays de la Loire region, France) and during two seasons: October 2015 and March 2016. The analytical protocol involved MP extraction from dried sediments using milliQ water and a centrifugation technique. After a filtration step of supernatants, MPs were detected and directly identified on the membrane filters using μFTIR spectroscopy in reflection mode. For the first time, the number of replicates allowing to obtain a satisfying representativeness of the whole sampled sediment was also evaluated at 10 replicates of 25 g each. The average number of MPs in sediments was 67 (±76) MPs/kg dw (N = 60) with no significant difference between sites and seasons. Ten different compositions of MPs were defined by μFT-IR with a high proportion of polypropylene (PP) and polyethylene (PE), 38 and 24%, respectively. Among MPs, mainly fragments (84%) were observed with main size classes corresponding to [>100 μm] and [50-100 μm] but no particles > 1 mm could be found suggesting that mainly small microplastics (<1 mm) were subject to vertical transport.

Fabrication of ordered honeycomb porous poly(vinyl chloride) thin film doped with a Schiff base and nickel(II) chloride

A modified poly(vinyl chloride) honeycomb thin film containing a low concentration of a thiadiazole Schiff base and nickel(II) chloride was successfully fabricated using the casting process. The surface morphology of the synthesized thin film was investigated using the scanning electronic microscopy. The synthesized poly(vinyl chloride) thin film was found to have a homogeneous surface morphology with a high crystalline nature. The addition of nickel(II) chloride was discovered to be vital for the formation of the honeycomb like structure.

Evaluation of ground calcite/water heavy media cyclone suspensions for production of residual plastic concentrates

Viable recycled residual plastic (RP) product(s) must be of sufficient quality to be reusable as a plastic or source of hydrocarbons or fuel. The varied composition and large volumes of such wastes usually requires a low cost, high through-put recycling method(s) to eliminate contaminants. Cyclone separation of plastics by density is proposed as a potential method of achieving separations of specific types of plastics. Three ground calcite separation medias of different grain size distributions were tested in a cylindrical cyclone to evaluate density separations at 1.09, 1.18 and 1.27 g/cm³. The differences in separation recoveries obtained with these medias by density offsets produced due to displacement of separation media solid particles within the cyclone caused by centrifugal settling is evaluated. The separation density at which 50% of the material of that density is recovered was found to increase from 0.010 to 0.026 g/cm³ as the separation media density increased from 1.09 to 1.27 g/cm³. All separation medias were found to have significantly low Ep₉₅values of 0.012-0.033 g/cm³. It is also demonstrated that the presence of an excess content of <10 µm calcite media particles (>75%) resulted in reduced separation efficiencies. It is shown that the optimum separations were achieved when the media density offset was 0.03-0.04 g/cm³. It is shown that effective heavy media cyclone separations of RP denser than 1.0 g/cm³ can produce three sets of mixed plastics containing: PS and ABS/SAN at densities of >1.0-1.09 g/cm³; PC, PMMA at a density of 1.09-1.18 g/cm³; and PVC and PET at a density of >1.27 g/cm³.

Release and Gas-Particle Partitioning Behaviors of Short-Chain Chlorinated Paraffins (SCCPs) During the Thermal Treatment of Polyvinyl Chloride Flooring

Chlorinated paraffin (CP) mixture is a common additive in polyvinyl chloride (PVC) products as a plasticizer and flame retardant. During the PVC plastic life cycle, intentional or incidental thermal processes inevitably cause an abrupt release of short-chain CPs (SCCPs). In this study, the thermal processing of PVC plastics was simulated by heating PVC flooring at 100-200 °C in a chamber. The 1 h thermal treatment caused the release of 1.9-10.7% of the embedded SCCPs. A developed emission model indicated that SCCP release was mainly controlled by material-gas partitioning at 100 °C. However, release control tended to be subjected to material-phase diffusion above 150 °C, especially for SCCP congeners with shorter carbon-chain lengths. A cascade impactor (NanoMoudi) was used to collect particles of different sizes and gas-phase SCCPs. The elevated temperature resulted in a higher partition of SCCPs from the gas-phase to particle-phase. SCCPs were not strongly inclined to form aerosol particles by nucleation, and less present in the Aitken mode particles. Junge-Pankow adsorption model well fitted the partitioning of SCCPs between the gas-phase and accumulation mode particles. Inhalation exposure estimation indicated that PVC processing and recycling workers could face a considerably high risk for exposure to SCCPs.

Separation of plastics by froth flotation. The role of size, shape and density of the particles

Over the last few years, new methods for plastic separation in mining have been developed. Froth flotation is one of these techniques, which is based on hydrophobicity differences between particles. Unlike minerals, most of the plastics are naturally hydrophobic, thus requiring the addition of chemicals that promote the selective wettability of one of its components, for a flotation separation. The floatability of six granulated post-consumer plastic - Polystyrene (PS), Polymethyl methacrylate (PMMA), Polyethylene Terephthalate (PET-S, PET-D) and Polyvinyl Chloride (PVC-M, PVC-D) - in the presence of tannic acid (wetting agent), and the performance of the flotation separation of five bi-component plastic mixtures - PS/PMMA, PS/PET-S, PS/PET-D, PS/PVC-M and PS/PVC-D - were evaluated. Moreover, the effect of the contact angle, density, size and shape of the particles was also analysed. Results showed that all plastics were naturally hydrophobic, with PS exhibiting the highest floatability. The contact angle and the flotation recovery of six plastics decreased with increasing tannic acid concentration, occurring depression of plastics at very low concentrations. Floatability differed also with the size and shape of plastic particles. For regular-shaped plastics (PS, PMMA and PVC-D) floatability decreased with the increase of particle size, while for lamellar-shaped particles (PET-D) floatability was slightly greater for coarser particles. Thus, plastic particles with small size, lamellar shape and low density present a greater floatability. The quality of separation varied with the mixture type, depending not only on the plastics hydrophobicity, but also on the size, density and shape of the particles, i.e. the particle weight. Flotation separation of plastics can be enhanced by differences in hydrophobicity. In addition, flotation separation improves if the most hydrophobic plastic, that floats, has a lamellar shape and lower density and if the most hydrophilic plastic, that sinks, has a regular shape and higher density. The results obtained show that froth flotation is a potential method for plastics separation, in particular for plastics with particle size greater than 2.0mm.

Thiamine hydrochloride (vitamin B1) as modifier agent for TiO2 nanoparticles and the optical, mechanical, and thermal properties of poly(vinyl chloride) composite films

In the present investigation, TiO₂ nanoparticles (NPs) were used for improving the thermal, mechanical and optical properties of poly(vinyl chloride) (PVC) matrix.

Flotation separation of waste plastics for recycling-A review

The sharp increase of plastic wastes results in great social and environmental pressures, and recycling, as an effective way currently available to reduce the negative impacts of plastic wastes, represents one of the most dynamic areas in the plastics industry today. Froth flotation is a promising method to solve the key problem of recycling process, namely separation of plastic mixtures. This review surveys recent literature on plastics flotation, focusing on specific features compared to ores flotation, strategies, methods and principles, flotation equipments, and current challenges. In terms of separation methods, plastics flotation is divided into gamma flotation, adsorption of reagents, surface modification and physical regulation.