pla processing
TRANSCRIPT
By- AKHIL K PAULOSE
PLA
PROCESSING
Poly(lactic acid) PLA is an aliphatic polyester made up of
lactic acid building blocks It is also biodegradable and compostable
TP derived from renewable plant resources such as sugar starch etc
PLA can be processed on standard processing equipment with minimum modification
Specific processing technologies are IM Extrusion casting , blow moulding ,blending etc………
PROCESSING OF PLA WHY PREDRYING?
Before processing of PLA, the polymer must be dried sufficiently to prevent excessive hydrolysis (molecular weight drop) which can compromise the physical properties of the polymer.
Typically the polymer is dried to less than 100ppm
Drying of PLA takes place in the temperature range of 80–100 ◦C
The required drying time is dependent on the drying temperature
Commercial grade PLA resin pellets are usually crystallized, which permits drying at higher temperatures to reduce the required drying time.
Amorphous pellets must be dried below the Tg (∼60 ◦C) to prevent the resin pellets from sticking together
PLA degrades at elevated temperatures and high relative humidity, the resins should be protected from hot and humid environments
INJECTION MOLDING Injection molding is the most widely
used converting process for thermoplastic articles, especially for those that are complex in shape and require high dimensional precision.
All injection molding machines have an extruder for plasticizing the polymer melt
Most injection molding machines for PLA are based on the reciprocating screw extruder, although two-stage systems
The extruder unit for injection molding machine is designed such the screw can reciprocate within the barrel to provide enough injection pressure to deliver the polymer melt into the mold cavities
The two-stage system consists an in-line extruder integrated to a shooting pot. The extruder plasticizes and feeds the melt into the shooting pot under relatively low injection pressure, from which the melt is injected into the hot runner under high pressure by a plunger in the shooting pot.
The two-stage system presents some advantages over its reciprocating counterpart, including shorter cycle time, small screw motor drive more consistent melt quality, and more consistent shot size
During the plasticizing process, PLA resin pellets are fed from a hopper near the end of a barrel.
The screw driven by an electric or hydraulic motor, rotates and transports the material towards the other end of the barrel.
The heat required for melting is provided by the heater bands wrapped around the barrel and frictional heat
The combined thermal energy from the heater and frictional heat due to friction between the plastic and the screw and barrel, provide sufficient heat to raise the PLA polymer above its melting point (170–180 ◦C) by the time it reaches the end of the barrel.
Typically the heater set point is usually set at 200–210 ◦C.
INJECTION MOLDING CYCLE
Cycle time is an important process parameter which is often minimized to maximize the production throughput.
To reduce the cycle time, it is quite common to transfer the partially cooled injection molded article to a post-mold cooling device
REFERENCE
EN.WIKIPEDIA.ORG/WIKI/CARBONNANOTUBES
WWW.SCIENCEDAILY.COM
HOW STUFF WORKS – WWW.HOWSTUFFWORKS.COM
IMAGES.GOOGLE.CO.IN/IMAGES
WWW.UNDERSTANDINGNANO.COM/NANOTUBES-CARBON.HTML
WWW.NANOCYL.COM › CNT EXPERTISE CENTRE
WWW.PA.MSU.EDU/CMP/CSC/NANOTUBE.HTML