Plastics PDF

Material which has had by far the biggest impact on the world of any material group. Its appearance does not possess plasticity, but properties of it do. **Dr. LH Baekeland** from Belgium discovered material called Feno formaldehyde plastics which is named "**Bakelite**". These plastics after that w...

Material which has had by far the biggest impact on the world of any material group. Its appearance does not possess plasticity, but properties of it do. **Dr. LH Baekeland** from Belgium discovered material called Feno formaldehyde plastics which is named "**Bakelite**". These plastics after that were used to produce light switches. From there plastics were supposed to replace many materials that were experiencing scarcity (niukkuutta). **[Composition]** Plastic is an organic material which is made of long molecular chains, called **macromolecules**. Hydrogen atoms bind carbon and complete the basic composition. Atoms like oxygen, nitrogen, sulfur, chlorine etc. can connect and it gives molecule certain properties. Components for manufacturing plastics are extracted from petroleum and natural gas, coal or minerals and natural substances like salt, limestone, water or wood. **Composition types:** **[Monomers & Polymers]** To synthesize plastic and to there by obtain macromolecules it is must to use **monomers**. **Monomers** Small molecules, comprised of carbon atoms that are bound twin bond. They are also building blocks that are used to make plastic macromolecules. **Polymerization** Monomers form covalent bonds by creating a long chain of **polymers**. **reaction** P**olymerization reactions** can be shared into two different categories which are **[*polycondensation* and *polyaddition*]** **Polycondensation** Brings together 2 different or identical substances. Reaction creates polymer with water, but it needs to be disposed of. E.g. plastics that are created from this reaction are polyester, polyether, polyamide **Polyaddition** Process of building polymer chain must be created step by step by bringing together two identical substances or 2 different substances. Orders of the atoms are changed compared to monomer. Process requires a catalyst and high pressure/temperature to work**.** In polyaddition reaction it doesn't create any byproducts. **Polyurethane** is formed by this technique **[Types of plastics ]** It can be separated into three different categories which are ***thermoplastics,** elastomers**, and thermosets*** **Thermoplastics** Long chains of molecules which are weakly interlinked by intermolecular bonds, **"Van der Waals" forces**. Links will break down under the heat (material starts to melt) which allows macromolecules to move around and slide among one another**.** Cooled down macromolecules forms links again hardens (solid). Thermoplastics become moldable and malleable when heated, but it does not change chemical composition. Forming **reversable** and **repeatable. polystyrene (PS), polyethylene (PE), polypropylene (PP), saturated polyesters, polymethylmethacrylate (PMMA), poly vinyl chloride (PVC)** **Thermosets** In thermosets polymers are interlinked with stronger, covalent bonds. Will not soften under the heat. In production mixing its chemical components and applying heat material hardens. Processing is **irreversible** and direct **recycling is not possible**. While thermosets have superiority mechanical, thermal and structural properties it loses irreversible, processability and recyclability. **polyurethane (PU), epoxy, unsaturated polyesters**. **Elastomers** Family of polymers with elastic properties. Elastomers show great elastic behavior on stress-strain diagram and returnable to original shape (5-10 times initial length). It includes silicone, and polyurethane based elastomers, Neoprene (trademarked by Dupont) and EPDMs (ethylene propylene diene monomers). Mostly they are thermosetting polymers and processing and recycling difficult. Less than 100 Celsius temperature resistance. **Natural rubber (NR) or latex, collected from rubber tree plantations.** **[Structure and composition ]** **Amorphous structure** It is disordered glassy, transparent and brittle (hauras). The reason for that is that there are long polymer chains which are entangled completely and irregularly. Only one being able to **produce transparent material**. Can be together strong covalent intermolecular bonds or weaker "Van der Waals" forces. **Crystalline structure** Long chains which are structurally aligned in a repeating pattern. Can again be both covalent bonds and Van der Waals forces. **Semicrystalline** Structure can be amorphous or crystalline. Partially ordered, crystallites with ductile loops, (can be) opaque and have better thermal resistance. **Copolymers** Polymer that are built out of several different monomers. **ABS (Acrylonitrile-Buthadiene-Styrene**) a low cost, versatile plastic, with excellent durability and impact resistance. It is often used **for automotive parts, food processors and Lego bricks.**  **[Additives & Agents]** **(lisäaineet/aineet)** By creating copolymers is possible to add desirable properties. Another way is to add various elements "**additives**" (represents **more than 10%** of the weight of a product) or **"agents"** (represent **less than 10%** of the weight of the finished product**)** **Additives** Examples of additives are **plasticizers** (more **flexible**), **fillers** (**save from shrinkage**, chemically inert materials), **stiffening agents** (more structure, enhance mechanical properties, limit shrinkage. Short fibers glass, carbon, aramid added) and **expanding agents** (to make foam) **Agents** Things that considered agents are **colorants/pigments, lubricants, anti-static agents** and **anti UV agents (**limit deterioration) **[Identifying plastics]** **International standard** 1. PET, polyethylene terephthalate **identifiers (thermopls**) 2. HDPE/PEHD, high-density polyethylene 3\. PVC, poly vinyl chloride\ 4. LDPE/PEBD, low-density polyethylene\ 5. PP, polypropylene\ 6. PS, polystyrene\ 7. Others, these are mainly high-performance thermoplastics, such as PC (polycarbonate, PMMA\ (polymethymethacrylate), PA (polyamide), etc. **[Methods of processing plastics]** For plastic there are four basic forms that they are supplied in (raw materials) **Powder** Used with rotation molding. **Pellets** Used with extrusion , injecting molding. **Sheets** Used with thermoforming. **Chemical components** Two or more substances are mixed, after which a polymerization reaction takes place. By applying heat or a catalyst (speeds up reaction). In the case of thermosetting plastics, the base materials are its chemical components, **often in liquid form**. **[Processing thermoplastics]** Plastics can be made softer or even viscous if heated up enough. It is possible to make it into complex shapes. In **crystalline thermoplastics** material will retain its mechanical properties much longer and then see sudden drop of elasticity modulus at high temperatures **Semi-crystalline** and **amorphous thermoplastics** have a more prominent softened state and turn viscous more quickly. **Glass state** Thermoplastics will be solid at room temperature and from there it can be machined or cut to make it finished products **Viscous state** Material behaves like **liquid,** so it is possible to apply processes like **extrusion** or **injection molding**. **Softened material** Is much more **plastic state**. It is possible to use processes such as **thermoforming** or **rotational molding**. **[Processing techniques for plastics]** **Rotational molding** piece by piece manufacturing procedure for **thermoplastics**. Can be used **to make large hollow (onto) bodies** without the need for welding (hitsaus) or bonding. Molds are relatively big, but not very complex or expensive. **Process takes a long time**, which adds significantly to the cost of the product. Thicker wall thickness is achievable, but there is **only little control over the actual thickness**. **Process:** **1.[Fine powder]** is placed into mold. **2**. After closing the mold starts rotating around two perpendicular axes and the powder starts to spread evenly over the inner surface. **3**. Entire setup goes to oven and heated until it fuses together. **4**. After cooling down plastic is solidified so can remove from mold. **Thermoforming** Process happens by **heating up a [sheet]** [ ] of a thermoplastic to point that it's softened and then placed on top of one-sided mold. By creating a vacuum between the sheet and the mold sheet takes over all details from the mold. **Quality** is usually **not very high** and therefore often used for **packaging materials**. Bigger parts can be made using thermoforming **like skylights, dashboards, panels for construction machines or agricultural machines**. Due to the process, wall thickness will vary throughout piece and that combined with the fact that only one side of the sheet comes into contact with mold it **is not accurate** (ei tarkka) **technique**. **Mechanical and aesthetic precision cannot be guaranteed**. **Extrusion Continuous manufacturing process** so it does not run in cycles, but it's an uninterrupted technique. Good choice when need to **create profiles, panels and sheets** since they are cut to desired length. **[Pellets]** are poured into a hopper heated cylinder. From there screw pushes the viscous material forward into a die (kuoppa). After cooling (through a bath of water) is finished, products are cut to length. **Extrusion blow** After normal extrusion (suulakepuristus) the matter is in a **rough tubular** **molding** **form (putkimainen)**. Material is placed into a mold and then the air pipe will be inserted, and air will be pushed in, forcing hot material against the mold. Extruded plastic bottle **can be recognized by the "scar**" that is visible at the bottom. "Scar" is pinch mark where mold closed and pinched material. (**Pellets)** **Blow film extrusion** Plastic is extruded **through a ring-shaped die** which creates **tubular sheet**. By inflating sheet, a thin film (kalvo) is created and once it's cooled the plastic bubbles flattens and wound onto reels. It is used to make **plastic bags** or **films. (Pellets)** **Injection molding** Fast process which is done piece-by-piece which is **widely used** because it gives **high quality molded objects without need for finishing** process required. It is possible to make complicated shapes and have extreme dimensional tolerances. Dimensions can vary from a few millimeters to several meters (some car bodywork, garden furniture). **Process:** **1**.For injection molding is used **plastic granules** (rae)that are melted by the heat and friction (kitka) in an injection screw **2**. Injected at high pressure to mold (between 500 and 1,500 bars). Mold is **closed by a system of hydraulics or motors**. **3**. Mold has a clamping force of several tons and includes a cooling system which makes material solidifies evenly **4**. The piece is removed after mold is opened. Molds are made of steel and are precision machined (expensive). Made in two parts (one fixed, mobile) which are hollowed to give cavity (ontelo) to products shape. Can have more than one cores. Inserts may also be placed into the mold which will stay in the injected piece, or decoration may be added which will be firmly fixed to the surface (\'in-mold\' procedures). To remove the mold (which will be reused several times), the shape of injected pieces must not lock the piece into the mold; it must have a draft angle (minimum 2%) to aid the removal of injected pieces. **The position of the joint planes is aesthetically crucial**. Always visible, they occur at each junction of the various parts of the mold. It is therefore best to study their position carefully during the mold design process, before the procedure begins. Finally, the channels through which the plastic flows towards the chamber (the runners) will also solidify their position, and that of any extractor's pins or plates, must also be carefully planned so that they leave only minimal traces on the final piece. These marks really identify an injected piece. In terms of production, injection molding remains viable from 100,000 up to 1,000,000 pieces. **[Variations for molding]** **Insert molding &** A part can be molded in several steps, giving the opportunity to use multi-**multi shot injection** plastics with different properties, or different finishes. **Gas-assisted injection** By injecting pressurized air into the mold after the plastic has been **molding** injected, we can create hollow parts. **Injection blow** Injection blow-molding is used to make fizzy drink bottles where the lid **molding** must be airtight.