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Airborne microplastics smaller than 5 mm in diameter can be easily inhaled by humans, impacting their health. The human exposure to microplastics can occur in indoor environments, and this study investigated the degree of indoor deposition of microplastics in settled dust. The authors assessed the relationship between the number of occupants/people and the amount of microplastics in their indoor environment by determining the indoor microplastic exposure in two offices, two schools, and two apartments in Surabaya, Indonesia. The settled dust was collected using a vacuum cleaner for 10 minutes on a single weekday and the weekend at each study location. The results show that the amount of microplastics collected at each location during workdays exceeded the amount found on weekends. The two offices sampled were found to have the greatest amounts of microplastics (334 particles on a weekday, 242 particles on a weekend; and 351 particles on a weekday, 252 particles on a weekend), and the two apartments produced the least amounts of microplastics (133 particles on a weekday, 127 particles on a weekend; and 108 particles on a weekday, 95 particles on a weekend). The dominant microplastic shape was that of fiber, and the dominant size range of the microplastics collected was 3000-3500 µm. The amount of indoor microplastics is influenced by the activities and the number of occupants/people in the space. The exposure levels indicated here will contribute to the formulation of the environmental health policy recommendations.

Recycled polypropylene (RPP) and lignin represent by-products produced in enormous amounts worldwide that remain underutilized. This study used rice straw lignin as a filler at various concentrations (0% to 70% w/w) in RPP and virgin polypropylene (PP) composites by melt blending. Structural and morphological alterations of lignin were analyzed by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), respectively. Mechanical properties were evaluated using a universal testing machine (UTM). Results revealed that the tensile strength of the composites decreased as the lignin content increased, presumably due to the low of compatibility degree of lignin and MAPP, as well as the crack formation due to the agglomeration of lignin. However, composites with lignin as a filler showed higher moduli and water absorption capacities, as well as thickness swelling; using lignin as a filler caused a drastic reduction of the elongation at break values. The results indicated that the physical and mechanical properties of RPP and its virgin PP composites had no substantial differences. This indicated that virgin PP could be substituted by recycled polypropylene (RPP) for composite applications with the addition of MAPP.

The thermally stimulated current (TSC) technique has been used to investigate molecular relaxation in poly(ethylene terephthalate) (PET) films unstretched and biaxially stretched at 90 and 95 °C. Unstretched PET films show two peaks at 77 and 90 °C corresponding to α and ρ relaxation processes, respectively. The α relaxation is associated with the main glass transition of the material. The ρ peak with lower intensity is attributable to permanent dipoles. Both biaxially stretched samples show one TSC peak at 95 °C, supposed to correspond to ρ relaxation. The disappearance of the α peak, accompanied by the displacement of the ρ peak to higher temperature, is the result of the higher thermal stability of the permanent dipoles, which is strongly influenced by the stiffening of amorphous parts and the crystallization by stretching. In both stretched samples, the continuous distribution of pre‐exponential factors over activation energies observed might correspond to a single relaxation mode. The kinematics of stretching PET has been discussed in terms of activation energy and temperature dependence of relaxation time. © 1999 Society of Chemical Industry

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