ChE 441. Paper Grades and Properties

Transcription

1 ChE 441 Paper Grades and Properties

2 Grades of Paper 1. Printing grades 2. Industrial grades 3. Tissues

3 Printing Grades Newsprint composed mainly of mechanical pulp, commonly used in printing newspaper Catalog lightweight newsprint; usually contains fillers Rotogravure uncoated newsprint type sheet, but more highly finished

4 Printing Grade Publication coated magazine paper, raw stock is usually mostly groundwood, but best quality use chemical pulp Banknote, Document high grade, permanent paper usually made from rag furnish

5 Printing Grade Bible light-weight, heavily loaded paper made from rag or chemical pulp furnish Bond, Ledger high quality papers used for letterheads and records. Furnish is either rag or chemical pulp Stationery relatively soft and bulky paper with good appearance. Usually chemical pulp furnish, but highest quality uses rag

6 Industrial Grades Bag high strength paper, usually made from highly refined unbleached pulp Linerboard lightweight board commonly used as the outer piles of corrugated box stock. Usually made from high-yield unbleached kraft with a better quality top liner for printing

7 Industrial Grades Construction paper a newsprint type sheet of higher weight and bulk Greaseproof dense nonporous paper made from highly refined sulfite pulp

8 Tissues Sanitary Tissues includes facial and toilet tissues, sanitary products and table napkins. Primary feature is softness and absorbency. Contains a high percentage of lightly refined chemical pulp Condenser tissue light-weight wellformed tissue made from highly refined kraft, used as a capacitor dielectric

9 Tissues Toweling creped absorbent paper usually made from lightly refined kraft with the addition of mechanical pulp Wrapping tissue this designation covers a variety of tissues made wrapping and packaging. The general requirement is strength, good formation and cleanliness

10 Physical Properties of Paper Ream A ream is a specified area of paper or paperboard, most frequently expressed in terms of a specified number of sheets (usually 500) of a certain dimension A 24 X 36 x500 ream means the combined area of 500 sheets each 24 in. by 36 in., for a total of 3000 ft The Tappi Standard ream is 1 square meter of paper or board

11 Physical Properties of Paper Grammage or Basis weight The weight of paper per ream, normally expressed on an air-dry basis (about 6-10% moisture, with 9% the standard) is known as the basis weight Printing paper is reported at 20 pounds per (24 in. X 36 in. x 500 sheet) ream Newsprint is 49 gsm (g/m 2 is the Tappi Standard unit)

12 Physical Properties of Paper Caliper The nominal thickness of paper is known as caliper All sheets above 0.3 mm thickness are classed as paperboard

13 Physical Properties of Paper Density, Bulk The density of a sheet of paper is its mass per unit volume The density of papers is typically g/cm 3 Bulk is the reciprocal of density and is expressed as cm 3 /g

14 Mechanical Properties of Paper: Tensile Strength Tensile strength is measured on paper strips 20 cm (7.9 in.) long by mm ( in.) wide using a constant rate of elongation according to TAPPI Standard T 494.

15 Mechanical Properties of Paper: Breaking Length The tensile strength of paper can be reported as a hypothetical length of paper that just supports its own weight when supported at one end The breaking length of most papers varies from 2.5 to 12 km

16 Mechanical Properties of Paper: Burst Strength The burst strength measures the amount of hydrostatic pressure (which increases at a specified rate) required to rupture a piece of paper The maximum pressure before rupture is measured in psi or kpa

17 ChE 441 Fiber from Recycled Paper

18 Introduction Secondary fiber is defined as any fibrous material that has already undergone a manufacturing process and is being recycled for another manufacturing process Broke from the dry end of the paper machine, finishing room trimmings, and repulped rolls could be considered as secondary fiber; but in practice, internal recycling is not included as part of secondary fiber utilization

19 Wastewater Grades Mixed paper: paper of varied quality (office waste, boxboard cuttings, mill wrappers, etc.) Old Newspapers (ONP) Old Corrugated Containers (OCC) Pulp substitutes: consisting of unprinted paper and board that has not been used (cuttings, shavings or trims) High-grade Deinked

20 Use of Recycled Papers Less than 20% of waste paper is deinked to be used in newsprint, tissue, or other bright grades Most waste paper is used in paperboards, chipboard, and roofing materials where color is not important The percentage of deinked newsprint and other grades is expected to increase considerably over the next few years

21 Shrinkage Shrinkage represents the loss of material from the original feedstock to the recovered product A plant that recovers 90 lb of dry fiber for every 100 lb of dry paper has a shrinkage of 10% A plant recovering OCC may have a shrinkage of about 8% A plant recovering newsprint for use in newsprint (news to news) may have a shrinkage of 15-20% for flotation deinking and up to 30% using combined flotation and washing deinking A plant recovering office paper and producing pulp of high brightness (above 85%) may have shrinkage of 35%

22 Repulping of Wastewater

23 Contaminant Removal Sources of Contaminants Centrifugal cleaners and screens are used

24 Deinking Deinking of pulp fibers is essentially a cleaning process where the ink is considered to be the dirt Chemicals along with heat and mechanical energy are used to dislodge the ink particles from the fibers and disperse them in the stock preparation Three specific types of chemicals are used Detergents Dispersants Foaming agents

25 Deink wash plant

26 Flotation Deinking Process

27 Combined Washing and Flotation

28 ChE 441 Environmental Impact

29 Measurement of Water Quality BOD COD TSS TOCl ph

30 Sources of Pollutants Water used in wood handling and barking Digester and evaporator condensates White water from screening and cleaning Bleach plant washer filtrates Paper machine white water Fiber and liquor spills from all sections

31 Aqueous Effluent Treatment Primary Treatment Secondary Treatment Tertiary Treatment Solid Handling

32 Air Quality Tests TRS SOX NOX NCG PM VOC

33 Sources of Air Pollutants Fine particulates fume from the recovery furnace Sulfur Oxides especially from sulfite mill operations Nitrogen oxides from all combustion processes Reduced sulfur gases mainly from kraft pulping and recovery operations Volatile organic compounds NCG from digester relief and spent liquor evaporation

34 Air Pollution Abetment Proper operation of recovery furnace Collection and incineration of noncondensables Scrubbers Mechanical collection of particulates