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