English and Literature
Submitted By vanecia23
There are two major mechanical pulps, thermo mechanical pulp (TMP) and groundwood pulp (GW). In the TMP process, wood is chipped and then fed into large steam-heated refiners where the chips are squeezed and fibreized between two steel discs. In the groundwood process, debarked logs are fed into grinders where they are pressed against rotating stones and fibreized. Mechanical pulping does not remove the lignin, so the yield is very high, >95%, but also causes paper made from this pulp to yellow and become brittle over time. Mechanical pulps have rather short fibre lengths and produce weak paper. Although large amounts of electrical energy are required to produce mechanical pulp, it costs less than chemical pulp.
Main article: deinking
Paper recycling processes can use either chemical or mechanical pulp. By mixing with water and applying mechanical action the hydrogen bonds in the paper can be broken and fibres separated again. Most recycled paper contains a proportion of virgin fibre in the interests of quality. Generally deinked pulp is of the same quality or lower than the collected paper it was made from.
There are three main classifications of recycled fibre:.
Mill Broke or Internal Mill Waste — this incorporates any substandard or grade-change paper made within the paper mill which then goes back into the manufacturing system to be repulped back into paper. Such out-of-specification paper is not sold and is therefore often not classified as genuine reclaimed recycled fibre. However, most paper mills have been recycling their own waste fibre for many years, long before recycling become popular.
Preconsumer Waste — this is offcuts and processing waste, such as guillotine trims and envelope blank waste. This waste is generated outside the paper mill and could potentially go to landfill, and is a genuine recycled fibre…...