Fiber and Filament ProductsFiber and Filament Products
Definitions:Definitions: FiberFiber - a long, thin strand whose length is at least 100 - a long, thin strand whose length is at least 100
times its cross‑section times its cross‑section FilamentFilament - a fiber of continuous length - a fiber of continuous length
Applications:Applications: Fibers and filaments for textilesFibers and filaments for textiles
Most important applicationMost important application Reinforcing materials in polymer composites Reinforcing materials in polymer composites
Growing application, but still small compared to Growing application, but still small compared to textilestextiles
Materials for Fibers and FilamentsMaterials for Fibers and Filaments
Fibers can be natural or synthetic Fibers can be natural or synthetic Natural fibers constitute ~ 25% of total marketNatural fibers constitute ~ 25% of total market
Cotton is by far the most important staple Cotton is by far the most important staple Wool production is significantly less than cottonWool production is significantly less than cotton
Synthetic fibers constitute ~ 75% of total fiber marketSynthetic fibers constitute ~ 75% of total fiber market Polyester is the most importantPolyester is the most important Others: nylon, acrylics, and rayon Others: nylon, acrylics, and rayon
Fiber and Filament Production - SpinningFiber and Filament Production - Spinning
For synthetic fibers, For synthetic fibers, spinningspinning = extrusion = extrusion of polymer melt or solution through a of polymer melt or solution through a spinneretspinneret, then drawing and winding , then drawing and winding onto a onto a bobbinbobbin
Spinneret = die with multiple small Spinneret = die with multiple small holesholes
The term is a holdover from methods The term is a holdover from methods used to draw and twist natural fibers used to draw and twist natural fibers into yarn or threadinto yarn or thread
Melt Spinning Melt Spinning Starting polymer is heated to molten state and Starting polymer is heated to molten state and
pumped through spinneretpumped through spinneret Typical spinneret is 6 mm (0.25 in) thick and Typical spinneret is 6 mm (0.25 in) thick and
contains approximately 50 holes of diameter 0.25 contains approximately 50 holes of diameter 0.25 mm (0.010 in)mm (0.010 in)
Filaments are drawn and air cooled before being Filaments are drawn and air cooled before being spooled onto bobbinspooled onto bobbin
Significant extension and thinning of filaments Significant extension and thinning of filaments occur while polymer is still molten, so final occur while polymer is still molten, so final diameter wound onto bobbin may be only 1/10 of diameter wound onto bobbin may be only 1/10 of extruded size extruded size
Used for polyester and nylonUsed for polyester and nylon filaments filaments
Figure : Melt spinning of Figure : Melt spinning of continuous filaments continuous filaments
Melt Spinning
ThermoformingThermoforming
Flat thermoplastic sheet or film is heated and deformed into Flat thermoplastic sheet or film is heated and deformed into desired shape using a molddesired shape using a mold
Heating usually accomplished by radiant electric heaters Heating usually accomplished by radiant electric heaters located on one or both sides of starting plastic sheet or located on one or both sides of starting plastic sheet or film film
Widely used in packaging of products and to fabricate Widely used in packaging of products and to fabricate large items such as bathtubs, contoured skylights, and large items such as bathtubs, contoured skylights, and internal door liners for refrigerators internal door liners for refrigerators
Figure : (1) a flat plastic sheet is Figure : (1) a flat plastic sheet is softened by heatingsoftened by heating
Vacuum Thermoforming
Figure : (2) the softened sheet is placed over Figure : (2) the softened sheet is placed over a concave mold cavitya concave mold cavity
Figure : (3) a vacuum draws Figure : (3) a vacuum draws the sheet into the cavitythe sheet into the cavity
Figure : (4) plastic hardens on contact with the Figure : (4) plastic hardens on contact with the cold mold surface, and the part is removed cold mold surface, and the part is removed and subsequently trimmed from the web.and subsequently trimmed from the web.
Figure : Use of a positive mold in vacuum thermoforming: (1) the Figure : Use of a positive mold in vacuum thermoforming: (1) the heated plastic sheet is positioned above the convex moldheated plastic sheet is positioned above the convex mold
Vacuum Thermoforming
Figure : Use of a positive mold in vacuum thermoforming: (2) the Figure : Use of a positive mold in vacuum thermoforming: (2) the clamp is lowered into position, draping the sheet over the mold as a clamp is lowered into position, draping the sheet over the mold as a vacuum forces the sheet against the mold surfacevacuum forces the sheet against the mold surface
Vacuum Thermoforming
Applications of ThermoformingApplications of Thermoforming Thin films: blister packs and skin packs for packaging Thin films: blister packs and skin packs for packaging
commodity products such as cosmetics, toiletries, small tools, commodity products such as cosmetics, toiletries, small tools, and fasteners (nails, screws, etc.) and fasteners (nails, screws, etc.) For best efficiency, filling process to containerize item(s) is For best efficiency, filling process to containerize item(s) is
displays and signs, bathtubs, certain toys, contoured skylights, displays and signs, bathtubs, certain toys, contoured skylights, internal door liners for refrigerators internal door liners for refrigerators
CastingCasting
Pouring liquid resin into a mold, using gravity to fill cavity, Pouring liquid resin into a mold, using gravity to fill cavity, where polymer hardens where polymer hardens
Both thermoplastics and thermosets are cast Both thermoplastics and thermosets are cast Thermoplastics: acrylics, polystyrene, polyamides Thermoplastics: acrylics, polystyrene, polyamides
(nylons) and PVC (nylons) and PVC Thermosetting polymers: polyurethane, unsaturated Thermosetting polymers: polyurethane, unsaturated
polyesters, phenolics, and epoxies polyesters, phenolics, and epoxies Simpler moldSimpler mold Suited to low quantitiesSuited to low quantities
Polymer Foam Polymer Foam
A polymer‑and‑gas mixture that gives the material A polymer‑and‑gas mixture that gives the material a porous or cellular structure a porous or cellular structure
Most common polymer foams: polystyrene Most common polymer foams: polystyrene (Styrofoam, a trademark), polyurethane (Styrofoam, a trademark), polyurethane
Other polymers: natural rubber ("foamed Other polymers: natural rubber ("foamed rubber") and polyvinylchloride (PVC) rubber") and polyvinylchloride (PVC)
Properties of a Foamed PolymerProperties of a Foamed Polymer
Low densityLow density High strength per unit weightHigh strength per unit weight Good thermal insulationGood thermal insulation Good energy absorbing qualities Good energy absorbing qualities
Classification of Polymer FoamsClassification of Polymer Foams
Elastomeric - matrix polymer is a rubber, Elastomeric - matrix polymer is a rubber, capable of large elastic deformationcapable of large elastic deformation
Flexible - matrix is a highly plasticized polymer Flexible - matrix is a highly plasticized polymer such as soft PVCsuch as soft PVC
Rigid - polymer is a stiff thermoplastic such as Rigid - polymer is a stiff thermoplastic such as polystyrene or a thermoset such as a phenolicpolystyrene or a thermoset such as a phenolic
Applications of Polymer FoamsApplications of Polymer Foams
Characteristic properties of polymer foams, and the Characteristic properties of polymer foams, and the ability to control elastic behavior by selection of base ability to control elastic behavior by selection of base polymer, make these materials suitable for certain polymer, make these materials suitable for certain applicationsapplications
Applications: hot beverage cups, heat insulating Applications: hot beverage cups, heat insulating structural materials, cores for structural panels, structural materials, cores for structural panels, packaging materials, cushion materials for furniture and packaging materials, cushion materials for furniture and bedding, padding for automobile dashboards, and bedding, padding for automobile dashboards, and products requiring buoyancy products requiring buoyancy
Extrusion of Polystyrene FoamsExtrusion of Polystyrene Foams
Polystyrene (PS) is a thermoplastic polymerPolystyrene (PS) is a thermoplastic polymer A physical or chemical blowing agent is fed A physical or chemical blowing agent is fed
into polymer melt near die end of extruder into polymer melt near die end of extruder barrel; thus, extrudate consists of expanded barrel; thus, extrudate consists of expanded polymer polymer
Products: large sheets and boards that are Products: large sheets and boards that are subsequently cut to size for heat insulation subsequently cut to size for heat insulation panels and sections panels and sections
Molding Processes for PS FoamsMolding Processes for PS Foams Expandable foam molding Expandable foam molding
Molding material consists of prefoamed Molding material consists of prefoamed polystyrene beadspolystyrene beads
Beads are fed into mold cavity where they Beads are fed into mold cavity where they are further expanded and fused together to are further expanded and fused together to form the molded product form the molded product
Products: hot beverage cupsProducts: hot beverage cups
Product Design Guidelines: GeneralProduct Design Guidelines: General
Strength and stiffnessStrength and stiffness Plastics are not as strong or stiff as metals Plastics are not as strong or stiff as metals Avoid applications where high stresses will be Avoid applications where high stresses will be
encountered encountered Creep resistance is also a limitation Creep resistance is also a limitation Strength‑to‑weight ratios for some plastics are Strength‑to‑weight ratios for some plastics are
competitive with metals in certain applications competitive with metals in certain applications
Product Design Guidelines: GeneralProduct Design Guidelines: General
Impact Resistance Impact Resistance Capacity of plastics to absorb impact is generally Capacity of plastics to absorb impact is generally
good; plastics compare favorably with most metalsgood; plastics compare favorably with most metals Service temperaturesService temperatures
Limited relative to metals and ceramics Limited relative to metals and ceramics Thermal expansion Thermal expansion
Dimensional changes due to temperature changes Dimensional changes due to temperature changes much more significant than for metals much more significant than for metals
Product Design Guidelines: GeneralProduct Design Guidelines: General
Many plastics are subject to degradation from sunlight Many plastics are subject to degradation from sunlight and other forms of radiation and other forms of radiation
Some plastics degrade in oxygen and ozone Some plastics degrade in oxygen and ozone atmospheresatmospheres
Plastics are soluble in many common solvents Plastics are soluble in many common solvents Plastics are resistant to conventional corrosion Plastics are resistant to conventional corrosion
mechanisms that afflict many metals mechanisms that afflict many metals
Rotational MoldingRotational Molding
Thermo plastics are thermosets can be formed into large parts Thermo plastics are thermosets can be formed into large parts by rotational moldingby rotational molding
A thin walled metal mold is made of 2 piecesA thin walled metal mold is made of 2 pieces
Rotated abut two perpendicular axesRotated abut two perpendicular axes
Pre-measured quantity of powdered plastic material is rotated Pre-measured quantity of powdered plastic material is rotated about 2-axesabout 2-axes
Typical parts produced-Trash cans, boat hulls, buckets, Typical parts produced-Trash cans, boat hulls, buckets, housings, toys, carrying cases and foot balls.housings, toys, carrying cases and foot balls.
RotationalRotational Molding Molding
Fig: The rotational Fig: The rotational molding (rotomolding molding (rotomolding or rotocasting) or rotocasting) process. Trash cans, process. Trash cans, buckets, and plastic buckets, and plastic footballs can be made footballs can be made by this process.by this process.
Thermoforming is a process of shaping flat thermoplastic sheet which includes two stages:
softening the sheet by heating, followed by forming it in the mold cavity.
There are three thermoforming methods, differing in the technique used for the forming stage:
Vacuum ThermoformingThe process involves shaping a preheated
thermoplastic sheet by means of vacuum produced in the mold cavity space.
The atmospheric pressure forces the soft sheet to deform in conformity with the cavity shape.
When the plastic comes into the contact with the mold surface it cools down and hardens.
Pressure Thermoforming
The process involves shaping a preheated thermoplastic sheet by means of air pressure. The air pressure forces the soft sheet to deform in conformity with the cavity shape.
When the plastic comes into the contact with the mold surface it cools down and hardens.
Mechanical ThermoformingThe process involves shaping a preheated thermoplastic
sheet by means of a direct mechanical force. A core plug (positive mold) forces the soft sheet to fill the
space between the plug and the negative mold. The process provides precise dimensional tolerance and
