315 MATE POLYMERS PROCESSING
Antonios Zavaliangos
Department of Materials Engineering Drexel University
Nylon
Everything came to an unfortunate halt with the outbreak of World War II, when nylon production was commandeered for the war effort. Women resorted to using makeup to decorate their legs, like drawing faux seams up the back of their legs with an eyebrow pencil.
The graduate (1968)
CHEMISTS Materials Engineers:
The linkage between processing structure & properties
CHEMICAL ENGINEERS
Polymers Processing
Goal: To convert raw plastics to useful final products with desirable properties Plastics Polymers (Plastics=Polymer+Additives)
Polyethylene is polymerized from ethylene a byproduct of the refining of crude oil and is a component of natural gas. A large oil company separates ethylene from crude oil in a refinery and sells the ethylene to a relatively small company that owns an ethylene pipeline. Ethylene pipelines exist throughout the southern United States along the Gulf Coast. The pipeline company is usually a small company due to the high liability associated with the maintenance of this critical system (pipelines periodically blow-up!). The pipeline industry is a highrisk/high-profit industry. Sales of ethylene, is a lower-risk, commodity industry that is basically subject to the price of oil.
Various grades offered by a large polyolefin producer are partly composed of blends of different branch content, molecular weight and density polyethylenes from different synthetic reaction conditions. A film blowing grade of polyethylene for clear bags might contain a blend of linear low density polyethylene, controlled branch content metallocene polyethylene and low density polyethylene. These blends might include polymers made in-house as well as some components from competitor olefin producers. Polyolefin producers often purchase or "rent" each others synthetic technology (license patents) and such patent royalties can often be a large component of profits for some polyolefin companies (Phillips Petroleum for instance). Blending of different grades and production of pellets from the usually powder reactor products involve a variety of processing steps and require process engineers. The polyethylene industry is a commodity product industry governed on the supply-side by the price of oil on the world market and on the demand-side by the consumer product, housing and automotive industries.
metallocene
An example: A shampoo bottle is injection molded from a high density grade of PE sold by a company such as Equistar. The shampoo is sold by a company like P&G and there is extensive interaction between them, although P&G may never purchase Equistar PE at all. The purchaser of the PE pellets is usually a small processing company that owns a number of injection molders and proprietary molds. The molds are provided by P&G, for instance, under a proprietary license to the processing company. The processing company is typically a high throughput, low profit margin facility and may be producing bottles from competitive brands in the same facility! In the end, the bottle for the shampoo product may represent only a small fraction of the total cost of the product (1 to 5 cents) but may be of utmost importance to the consumer product company in terms of product recognition and in terms of effective storage and dispensing of the product.
RAW MATERIALS
Most polymers are supplied in particulate form (pellets, beads, granulates) which is convenient
transport and handle blend (with additives) and compound store feed and process
m < Size < mm
MIXING
Additives - a wide range of second phases added to polymers for processing and/or properties
Stabilizers (degradation), (pigments Colors and dies), Plasticizers (molecular level) Fillers and Reinforcements, Lubricants (granule level).
Other polymers (co-extrusion, co-injection molding etc.) UNIFORMITY IS A MAJOR ISSUE!...
DEVOLATILIZATION
Entrapped air (between granules)
source of defects
Absorbed gases and humidity
greatly affect processing and properties
PROCESSING IN THE MELT
The majority of processing operations for polymers are performed in the liquid stage at temperatures between RT and 300400oC Essential knowledge:
thermal aspects of melting cooling and effect on properties
Melting is often the rate limiting step!...
FLOW UNDER PRESSURE
The molten plastic is forced through channels in order to be shaped into products. Size of machine is an issue.
EXTRUSION (80% of plastics processed by extrusion) INJECTION MOLDING BLOW MOLDING THERMOFORMING COMPRESSION MOLDING
FINISHED PRODUCTS
Die forming
(profiles, fibers, blow molding)
Molding
(conventional, reaction molding, compression molding, casting, blow molding)
Secondary shaping
(fiber stretching, blowing, thermoforming)
Calendering and coating Mold coating
PROPERTIES
Shape/Size Tolerances Mechanical Properties Optical Properties Electrical Properties Appearance and Aesthetics
FUNDAMENTAL KNOWLEDGE REQUIREMENTS
Transport phenomena Mixing principles Solid Mechanics Polymer Melt Rheology Polymer Physics (Properties) Polymer Chemistry
OTHER ISSUES
Empiricism vs Mathematical Modeling Computer Modeling. Equipment and Automatic Control Properties, and Quality (control, statistics) Cost, Investment, Financial Issues
EXTRUSION
FIBER SPINNING
FLAT FILM FORMING
TUBULAR FILM BLOWING
INJECTION MOLDING
BLOW MOLDING
THERMOFORMING
ROTATIONAL MOLDING
CASTING
REACTION INJECTION MOLDING
COMPRESSION MOLDING
CALENDERING
COATING
POLTRUSION
High quality composites
PROCESSING AND PROPERTIES A case study
Film blow molding of polybutelyne (PB1)
most film made by PE but PB1 is cheaper obtaining good properties is an issue
Processing
Pellets are feed into an extruder The melt is homogenized and pressurized through a slit die Air is blowing through the center of the die to expand the bubble
Film blow molding of polybute...