262 Introduction to Renewable Biomaterials
Table 8.17Mechanical properties of polyolefin–old newspaper composites compared to
polyolefin–glass fibre composites.
Composites
(numbers represent
ratios)
Izod impact
energy notched
(J m−^1 )
Izod impact
energy
unnotched (J m−^1 )
Tensile
modulus
(GPa)
Tensile
strength
(MPa) Publication
PP60/ONF40 20.8±0.5 112 ± 18 4.42±0.2 34.1±1.1 [65]
PP60/ONF40/MAPP3 21.6±0.1 212 ± 24 57.0±0.7 [65]
PP80/ONF20 2.8±0.1 [70]
PP70/ONF30 3.8±0.1 [70]
PP60/ONF40 4.2±0.1 [70]
PP50/ONF50 5.3±0.2 [70]
PP80/GF20 4.1±0.1 [70]
PP70/GF30 5.7±0.1 [70]
PP60/GF40 7.7±0.1 [70]
PP90/ONF10/MAPP5 2.7 44 [67]
PP80/ONF20/MAPP5 3.0 50 [67]
PP70/ONF30/MAPP5 3.3 58 [67]
PP – polypropylene, ONFs – old newspaper fibres, MAPP – polypropylene-grafted-maleic anhydride,
GF – glass fibre.
of paper sludge depend on raw materials, the paper grade being manufactured, the
amount of water used and the cleaning technique used for wastewater. Wood, cellulose
fibres, lignin and organic binders are the main organic components, while kaolinite and
calcium carbonate are the main inorganic ones [72]. Generally, paper sludge is disposed
in landfills; as a consequence many researchers focused their attention on the potential
use of this waste charge in composite materials.
Hamzeh, Ashori and Mirzaei have proposed an interesting study, introducing waste
paper sludge in high-density polyethylene–WF composites [73]. They analysed different
concentrations (20, 30, 40 and 60 wt%) of two sludge materials: one derived from
wastewater treatment used in paper industries and the other ink-eliminated sludge,
derived from the recycling treatment of waste paper. This study suggests that waste
sludge can be used as reinforcing filler for thermoplastic composites: in fact, composites
with paper sludge addition have shown better properties (except for some samples)
in terms of flexural properties and water absorption uptake. Similar results were also
obtained by Son [74], investigating the effect of different paper sludge’s mixing ratio
and types, as well as concentration of coupling agents on the physical and mechanical
properties of paper sludge–thermoplastic composites. They analysed the dimensional
stability of the composites, founding its increase with paper sludge content. From a
mechanical point of view, they also confirmed the effect of paper sludge as reinforce-
ment, regarding flexural strength. These two aspects can be seen in Figures 8.18 and 8.19.
The extraction process adopted to obtain fibres from waste paper directly affected
the properties of the resulting composites. The choice depends on the application of the
produced material. Valenteet al. grinding waste paper with two different equipment
(a mill working by impact shear and turbulence and a knife-mill), obtaining distinct
mechanical properties, optimized for the applications [75].
