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Lactide: Lactic Acid Condensed and Cracked under Vacuum, Recrystallised
Charlie

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Charlie

19. uMfumfu 2026DE
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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.
Osezingeni eliphezulu
1–2 days

Imiyalelo

1

Drive off the water

Distil the lactic acid at atmospheric pressure at 120–130 °C until nearly all the water of dilution has gone.

Izinto zokwakha zalesi sinyathelo:

I-Lactic Acid (yezobuchwepheshe)I-Lactic Acid (yezobuchwepheshe)1 ucezu

Amathuluzi adingekayo:

Ibhodlela elinesisekelo esiyindilingaIbhodlela elinesisekelo esiyindilinga
Ugoqo lwe-condenserUgoqo lwe-condenser
Ipuleti ElishisayoIpuleti Elishisayo
Ibhavu LikawoyelaIbhavu Likawoyela
Ithemomitha YaselabhorethriIthemomitha Yaselabhorethri
2

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).

Amathuluzi adingekayo:

Iphampu yomoyaIphampu yomoya
Isilinganiso sokungabi namoyaIsilinganiso sokungabi namoya
Isixhaphi esibandayoIsixhaphi esibandayo
Ibhavu LikawoyelaIbhavu Likawoyela
Ithemomitha YaselabhorethriIthemomitha Yaselabhorethri
3

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.

Amathuluzi adingekayo:

Iphampu yomoyaIphampu yomoya
Isilinganiso sokungabi namoyaIsilinganiso sokungabi namoya
Ugoqo lwe-condenserUgoqo lwe-condenser
Ibhavu LikawoyelaIbhavu Likawoyela
Ithemomitha YaselabhorethriIthemomitha Yaselabhorethri
Amagilavu Amelana NokushisaAmagilavu Amelana Nokushisa
4

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.

Amathuluzi adingekayo:

I-Ethyl AcetateI-Ethyl Acetate
Ibhikha Lengilazi Elimelana NokushisaIbhikha Lengilazi Elimelana Nokushisa
Ipuleti ElishisayoIpuleti Elishisayo
I-funnel ye-Büchner (i-porcelain)I-funnel ye-Büchner (i-porcelain)
Iphepha LokuhluzaIphepha Lokuhluza
Izibuko Zokuchitheka KwamakhemikhaliIzibuko Zokuchitheka Kwamakhemikhali
5

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.

Amathuluzi adingekayo:

Ishubhu lengilazi elincane kakhuluIshubhu lengilazi elincane kakhulu
Ithemomitha YaselabhorethriIthemomitha Yaselabhorethri
Ibhavu LikawoyelaIbhavu Likawoyela

Izinto

1

Amathuluzi Adingekayo

15

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Lactic Acid: Glucose Fermented over Chalk, Freed with Sulphuric Acid
Yingozi

Lactic Acid: Glucose Fermented over Chalk, Freed with Sulphuric Acid

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Ethyl Acetate: Alcohol, Sulphuric Acid and Sodium Acetate Distilled
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Ethyl Acetate: Alcohol, Sulphuric Acid and Sodium Acetate Distilled

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