It is made of pure cellulose, in particular it has a high content in long alpha-cellulose fibers extracted from linters of cotton.
its specific weight varies depending on the application. Most common grades weight around 65 to 100 g/m2. Some thicker filter can weight up to 200 g/m2, more than that and it's more an absorbent paper than a filter.
No. Membranes are thin sub-micron filters with well defined pores. They are more like a regular 2D mesh with no loading capacity. Filter paper are 3D depth filters that can hold particulate in their thickness. Also filter paper is made of tangled fibers, they don't have well defined pores unlike membranes.
For some applications like chromatography, filter paper can be made polar.
Quantitative paper is used to recover the precipitate (quantify it) while qualitative paper is more for removing the unwanted precipitate and recover the solution instead.
It's another name for quantitative filter paper. To measure the quantity of a precipitate, a solution is filtered with quantitative paper. The precipitate and paper are then burned together. Because quantitative paper contains very little ashes (ashless), only the precipitate remains after ashing.
Sometimes the precipitate needs to be recovered by scraping the filter. To prevent tearing of the paper, a resin binder is added to wet-strengthened qualitative filter paper (91, 114...). Because the binder introduce ashes, wet-strenghtened quantitative filters (5x) are made a bit differently and called hardened low-ash grades. To eliminate ashes totaly, hardened ashless grades (54x) can also be hardened with acid instead of a binder, in this case they are both wet-strengthened and chemical resistant.
By far the most sold grade is Qualitative grade 1 as it's a general polyvalent grade with many applications then Grade 2 and 4. For Quantitative grades, 40, 41 and 42 are the most popular.
Usually it's a disk that has been folded in a quarter (quadrant) to form a connical shape fitting a standard 60 ° funnel. There are a few variations to spread the filtration more evenly or ensure the quadrant stick to the funnel.
Unlike quadrants, fluted filters don't have a simple smooth conical shape, they have pleats all around, like accordions. For storage they are packed tightly and held in little triangular stacks with sleeves.
Gravity filtration can be slow, especially when a high retention is required. Fluted filter paper can increase filtration speed and loading capacity significantly.
Pleating the filter increase its effective filtration area by reducing the contact with the funnel. This larger area means there are more pores available so the clogging takes longer. As a consequence filtration flow and loading capacity are higher.