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Lactide: Lactic Acid Condensed and Cracked under Vacuum, Recrystallised
Lactide is the ring-shaped double molecule of lactic acid, the monomer from which PLA is made. Schneider's du Pont patent (US 2,703,316, 1955) drives the water out of lactic acid, condenses it under vacuum to a syrupy low polymer, then heats that to 200–250 °C at 8–10 mm so that lactide distils off. For a tough plastic it must be very pure: recrystallise it from ethyl acetate until it melts at 120 °C or higher (best 123–125 °C).
The picture: our diagram.
Abantado
1–2 days
Mga Tagubilin
1
1
Drive off the water
Drive off the water
Distil the lactic acid at atmospheric pressure at 120–130 °C until nearly all the water of dilution has gone.
Mga materyales para sa hakbang na ito:
Lactic Acid (teknikal)1 pirasoMga kailangang kasangkapan:
Prasko na bilog ang ilalim
Ikid ng kondensador
Pang-init na Plato
Oil Bath
Termometrong Panlaboratoryo2
2
Condense under vacuum
Condense under vacuum
Continue distilling under 17–35 mm of mercury. Water of esterification comes off and the acid becomes a syrupy low polymer (polylactic acid).
Mga kailangang kasangkapan:
Bombang panghigop ng hangin
Panukat ng bakyum
Cold TrapOil BathTermometrong Panlaboratoryo3
3
Crack to lactide
Crack to lactide
Lower the pressure to 8–10 mm and raise the temperature to 200–250 °C. Lactide distils at 130–140 °C (10–13 mm) and sets to a soft crystalline solid.
Mga kailangang kasangkapan:
Bombang panghigop ng hanginPanukat ng bakyumIkid ng kondensadorOil BathTermometrong Panlaboratoryo
Guwantes na Matibay sa Init4
4
Recrystallise from ethyl acetate
Recrystallise from ethyl acetate
Recrystallise the crude lactide from ethyl acetate, filter and dry. Repeat: in the patent the melting point rose from 114–115 °C after the first crystallisation to 118, 123–124 and 124–125 °C after the fourth.
Mga kailangang kasangkapan:
Ethyl Acetate
Basong Salamin na Matibay sa InitPang-init na Plato
Embudong Büchner (porselana)
Papel na Pansala
Salamin Laban sa Tilamsik ng Kemikal5
5
Check the melting point
Check the melting point
Put a few crystals in a capillary tube and warm slowly. Lactide melting at 120 °C or above is fit for making PLA; below 120 °C it gives a brittle polymer.
Mga kailangang kasangkapan:
Manipis na tubong salaminTermometrong PanlaboratoryoOil BathMga Materyales
1- 1 pirasoPlaceholder
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