Materials Flashcards
How is wood pulp produced?
My homework answer
Four step process:
- Get timber and debark it
- Place the demarked timber in the chipping machine and this wood becomes pulp
- Then clean and bleach the pulp
- Wash and dry the pulp
How is mechanical wood pulp produced?
My homework answer
Mechanical pulp is produced when the wood fibres are reduced to smaller fibres by a mechanical grinding process
How is chemical wood pulp produced?
My homework answer
Chemical pulp is produced when logs first get chopped into wood chips which are than cooked with chemicals under a high pressure
How is thermo-mechanical wood pulp produced?
My homework answer
Thermo-mechanical pulp is produced when the wood fibres are heated and softened in a steaming process before they are grinded.
What are the by-products of the wood pulling process?
A by-product is an incidental or secondary product made in the manufacture or synthesis of something else. The by-products of wood pulp are: tissue, lignum and ethyl alcohol.
How is the by-product of wood pulp, tissue made?
Tissue is made by recycled wood pulp. It’s produced on the papermaking machine which is also known as the fourdrinier machine
How is the by-product of wood pulp, lignum made?
Lignum is a glue-like substance which holds wood cells together and makes trees strong. During the cooking process of wood pulp, toxic chemicals are used to remove lignin. And any remaining lignin has to be bleached out of the pulp, because lignin has to be bleached out of the pulp, because lignin causes paper to turn yellow.
Name the four steps in the fourdrinier process
Wet end, press section, drying section and calendar stack
What happens during the first stage of the fourdrinier process, wet end?
The wet end starts with the wood pulp diluted to 99% water and 1% fibre to form a slurry that is held in the head box. A continuous stream of slurry is pumped from the head box through an adjustable slit (called the slice) onto a moving gauze wire belt that vibrates to drain off some of the water and allow the fibres to interweave. Raised patterns formed in the gauze create the watermark - a feature in many high-quality writing papers
What happens during the second stage of the fourdrinier process, press section?
The press section uses a system of nip presses or rollers that wrings out the majority of excess water from the pulp and stretches it out into a rough paper. It is at this stage that the thickness of the paper/board is determined. The gap between the press rollers us adjusted to allow for differing thicknesses such as card. The term card usually refers to paper which has a density greater than 160gsm (grams per square metre)
What happens during the third stage of the fourdrinier process, drying section?
The dryer section dries the paper using a series of steam-heated rollers by removing the moisture (just like ironing clothes.) The resulting paper has a water content of 4-6 % and sizing agents, starches and resins can be added to enhance the papers properties
What happens during the fourth stage of the fourdrinier process, calendar stack?
The calendar section comprises a series of rollers through which the paper is fed in order to smooth it out and give it a uniform thickness. The pressure applied to the paper by these rollers determines the finish of the paper
How is mechanical pulp produced?
Textbook
The logs of coniferous trees are saturated with water and de-barked. The wood is ground down, which softens the lignin, the mechanised forces departed the fibres to form ‘groundwood pulp’. This pulp is screened to accept 1-2mm pieces, with larger pieces being re-circulated for additional screening. The resulting pulp can only be used for low-grade paper such as newspaper, so the pulp is bleached with peroxide or sodium hydroxide. This is the most widely used method in the uk for producing wood pulp.
How is chemical pulp produced?
Textbook
After de-barking, the hard- and softwood logs are cut into 2cm chips along the grain. These are pounded into fragments and screened. The resulting pulp is stored and treated with either an acid or an alkali to break down the lignin. Most chemical pulp is made by the alkaline Kraft process, or sulphate to ‘cool’ the wood pulp. The amount of fibres are longer, stronger and contain fewer impurities.
How is waste pulp produced?
Textbook
Recycled paper and board used for waste pulp is often used for lower grades of paper, as its strength, durability and colour are not as good as virgin fibres (produced using mechanical and chemical methods). Waste pulp is often mixed with virgin fibres to produce better quality papers as fibres become shorter and weaker and lose their papermaking qualities
What is wood pulp?
Wood pulp is fibre which has been reduced chemically or mechanically to pulp and then is used in the manufacture of paper. There are many different types of wood pulp but there are a few main ones: chemical, mechanical and waste
Thermoplastics
PET
Polyethylene terephthalate
ID code
1
Thermoplastics
HDPE
High density polyethylene
ID code
2
Thermoplastics
PVC
Polyvinyl chloride
ID code
3
Thermoplastics
LDPE
Low density polyethylene
ID code
4
Thermoplastics
PP
Polyethylene
ID code
5
Thermoplastics
PS
Polystyrene
ID code
6
Polymers
What are the main advantages of using thermoplastics in commercial packaging?
- lightweight and versatile
- strong, tough, rigid, durable, and impact and water resistant
- easily formed and moulded
- easily printed on
- inexpensive
- recyclable
What is the general idea of thermoplastics?
You can heat it and shape the material multiple times
What is the general idea of thermosetting plastics?
You can only hear and shape the material once. After that, it stays in that shape
Metals
Define ferrous metals
Which contain mainly ferrite or iron i.e. Steel. It also includes those with small additions of other substances e.g. Carbon steels almost all are magnetic
Metals
Define non-ferrous metals
Which contain no iron r.g. Aluminium and tin. They are not magnetic
Metals
Define alloys
Which are formed by mixing two or more metals and, on occasion, other elements to produce metals with enhanced properties e.g. Stainless steel (steel alloy) and duralumin (aluminium alloy)
What are the advantages of using metals for commercial packaging?
- added security, as sealed cans cannot be tampered with without obvious viable signs
- containers can be made in a variety of standard sizes and shapes e.g. Drinks cans, and custom-made styles e.g. Chocolate and biscuit tins
- containers can be embossed or de-bossed to provide surface, textures and visual appeal
- metals can be directly printed on to or a paper label added for total graphic coverage, providing an effective point-of-sale display
Alloy - Stainless steel
Composition - carbon steel (87%) strength and rigidity, chromium (13%) resistance to wear and corrosion
Properties - advantages
- excellent resistance to corrosion, oxidation (rust) and staining
- high-quality surface finish
- low maintenance
- 100% recyclable
Alloy - Stainless steel
Composition - carbon steel (87%) strength and rigidity, chromium (13%) resistance to wear and corrosion
Properties - disadvantages
- relatively expensive
* relatively hard to machine
Alloy - Stainless steel
Composition - carbon steel (87%) strength and rigidity, chromium (13%) resistance to wear and corrosion
Applications
With over 150 grades available (increasing the chromium content up to 26% for harsh environments), there are a wide range of applications, including:
Cutlery, jewellery, cookware, sterile surgical instruments, building construction, etc
Alloy - duralumin
Composition- aluminium (93.5%) strength and lightness, copper (4.4%) strength, magnesium (1.5%) alloying agent (strength and lightness), manganese (0.6%) deoxidising (removing oxygen)
Properties - advantages
- excellent strength to weight ratio
- extremely hard and tough
- highly resistant to stress - corrosion cracking
- machines and casts well
- high performance in extreme temperatures
Alloy - duralumin
Composition- aluminium (93.5%) strength and lightness, copper (4.4%) strength, magnesium (1.5%) alloying agent (strength and lightness), manganese (0.6%) deoxidising (removing oxygen)
Properties - disadvantages
- can suffer from corrosion
* becomes brittle through fatigue
Alloy - duralumin
Composition- aluminium (93.5%) strength and lightness, copper (4.4%) strength, magnesium (1.5%) alloying agent (strength and lightness), manganese (0.6%) deoxidising (removing oxygen)
Applications
Applications make use of its excellent strength to weight ratio and casting ability, including: aircraft and vehicle structures (shells and frames), precision tools and components including bicycle and engine parts, etc.
Thermoplastics
PET - 1
Properties
- excellent barrier against atmospheric gases
- prevents gas from escaping package
- does not flavour the contents
- sparkling ‘crystal clear’ appearance
- very tough
- lightweight - low density
Thermoplastic
PET - 1
Applications
Carbonated (fizzy drinks) bottles.
Packaging for highly flavoured food.
Microwaveable food trays.
Thermoplastics
HDPE - 2
Properties
- highly resistant to chemicals
- good barrier to water
- tough and hard wearing
- decorative when coloured
- lightweight and floats on water
- rigid
Thermoplastics
HDPE - 2
Applications
Unbreakable bottles (for washing-up liquid, detergents, cosmetics, toiletries, etc). Very thin packaging sheets.
Thermoplastics
PVC - 3
Properties
- weather resistant - does not rot
- chemical resistant - does not corrode
- protects products from moisture and gases while holding-in preserving gases
- strong, good abrasive resistance and tough
- can be manufactured either rigid or flexible
Thermoplastics
PVC - 3
Applications
Packaging for toiletries, pharmaceutical products, food and confectionery, water and fruit juices.
Thermoplastics
LDPE - 4
Properties
- good resistance to chemicals
- good barrier to water, but not gases
- tough and hard wearing
- decorative when coloured
- very light and floats on water
- very flexible
Thermoplastics
LDPE - 4
Applications
Stretch wrapping (cling film), milk carton coatings.
Thermoplastics
PP - 5
Properties
- lightweight
- rigid
- excellent chemical resistance
- versatile - can be stiffer than polyethylene or very flexible
- low moisture absorption
- good impact resistance
Thermoplastics
PP - 5
Applications
Food packaging - yoghurt and margarine pots, sweet and snack wrappers.
Used for laminating paper and board.
Thermoplastics
PS - 6
Properties
Rigid polystyrene: - transparent - rigid - lightweight - low water absorption Expanded polystyrene: - excellent impact resistance - very good heat insulation - durable - lightweight - low water absorption
Thermoplastics
PS - 6
Applications
Rigid:
Food packaging, e.g. Yoghurt pots, CD Jewel cases, audio cassette cases.
Expanded:
Egg cartoons, fruit, vegetable and meat trays, cups, etc. Packing for electrical and fragile products.
Rigid PVC (poly vinyl chloride) Cost
Medium
Polystyrene (high impact polystyrene)
Cost
Low
ABS (acrylonitrile butadienestyrene)
Cost
Medium
Nylon (polyamide)
Cost
High
Polyester resin (unsaturated polyester resin) Cost
Medium
Low density polythene (low density polyethylene)
Cost
Medium
High density polystyrene (high density polyethylene)
Cost
Medium
Plasticised PVC (polyvinyl chloride) Cost
Medium
Expanded polystyrene (expanded polyphenylethane) Cost
Low
Acrylic (polymethyl methacrylate)
Cost
Medium
