João Moura Bordado

Improved adhesion of polyethylene by copolymerisation of ethylene with polar monomers

Abstract The inertness of polyethylene restricts its compatibility with other materials. Thus, the adhesion between polyethylene and various substrates usually requires surface pretreatments on the polyolefin in order to obtain satisfactory results. One different approach is the production of ethylene copolymers with small amounts of polar comonomers that can act as adhesion promoters. Using metallocene based catalysts, ethylene copolymers with 10-undecenoic acid (UA) and with 5,7-dimethylocta-1,6-diene (5,7DMO) were synthesised. The adhesion strengths of the copolymers in direct tension were measured. The obtained results show that UA/ethylene and 5,7DMO/ethylene copolymers exhibit higher adhesion strengths with increasing comonomer contents. UA/ethylene copolymers are more effective in improving adhesion properties than 5,7DMO/ethylene copolymers. This difference is easily understandable on the basis of the polarities of both comonomers.

Exposure to airborne ultrafine particles from cooking in Portuguese homes

Cooking was found to be a main source of submicrometer and ultrafine aerosols from gas combustion in stoves. Therefore, this study consisted of the determination of the alveolar deposited surface area due to aerosols resulting from common domestic cooking activities (boiling fish, vegetables, or pasta, and frying hamburgers and eggs). The concentration of ultrafine particles during the cooking events significantly increased from a baseline of 42.7 μm2/cm3 (increased to 72.9 μm2/cm3 due to gas burning) to a maximum of 890.3 μm2/cm3 measured during fish boiling in water, and a maximum of 4500 μm2/cm3 during meat frying. This clearly shows that a domestic activity such as cooking can lead to exposures as high as those of occupational exposure activities. Implications: The approach of this study considers the determination of alveolar deposited surface area of aerosols generated from cooking activities, namely, typical Portuguese dishes. This type of measurement has not been done so far, in spite of the recognition that cooking activity is a main source of submicrometer and ultrafine aerosols. The results have shown that the levels of generated aerosols surpass the outdoor concentrations in a major European town, which calls for further determinations, contributing to a better assessment of exposure of individuals to domestic activities such as this one.