Utilization of recycled polypropylene, cellulose and newsprint fibres for production of green composites

This work investigates the feasibility of using the recycled polypropylene (rPP), cellulose (CF) and newsprint (NP) fibres in polyolefin reinforced composites. Recycled PP filled with 40 wt.% of cellulose (rPP/CF) or newsprint (rPP/NP), with the addition of impact modifier (IM) and compatibilizing agent (CA), have been prepared with ex-trusion melting and injection moulding. Melting and crystallization behaviour of plain matrix and composites were measured by differential scanning calorimetry (DSC). Morphological and mechanical properties were also studied using scanning electron microscope (SEM) and tensile testing, respectively. Thermal stability of composites was similar to neat rPP for both types of the filler used. Though, the crystallinity was progressively decreased with the addition of CF or NP. The DSC further revealed an occurrence of the two distinct melting transitions, meaning that the examined materials were not based on pure polypropylene (PP), but are rather blends of high-density polyethylene (HDPE) and PP, what has been confirmed also by the Fourier transform infrared spectroscopy (FTIR). The largest single source of contaminations in recycled PP comes from HDPE since both polymers are identified by a similar density and can be accidentally mixed during the conventional physical separation process. Composites reinforced with CF have shown better mechanical performances than those based on reclaimed NP fibres, what can be attributed to the initial fibre quality. Tensile strength of the composites filled with CF and NP fibres was 36 MPa and 29 MPa, respectively, in disparity to 23 MPa measured for neat rPP. The fibre addition further resulted in substantial increase in Young modulus of the composites. The addition of CF and NP fibres lead to an improved modulus of elasticity by 16 and 47%, respectively. Waste paper in the form of recovered cellulose or reclaimed newsprint fibre can thus meet all the technical requirements to become an alternative to inor-ganic fillers in thermoplastic composites

Measurements of the quantum efficiency of CsI photocathodes in a multiwire proportional chamber

The quantum efficiency of reflective CsI photocathodes in a multiwire proportional chamber (MWPC) has been measured. The MWPC is operated with methane at room temperature and atmospheric pressure and a gas gain of about 105. Two different methods are used to determine the quantum efficiency (QE). The first uses Cherenkov radiation of β-particles in a 1 cm thick NaF window of the CsI-MWPC and measures the average ratio of the CsI quantum efficiency to a standard QEs (λ) used in simulation. The second method uses a monochromator and compares the count rates of the CsI-MWPC with the count rates of a Philips XP2020Q photomultiplier. Results are presented for the dependence of the quantum efficiency on the photocathode production procedure, on the substrate material, on the thickness of the CsI layer, on exposure time to ambient air, on healing of the photocathodes, on flushing them with methane and on the cumulative charge collected