BBC Focus - 03.2020

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Retailers are beginning to switch from single-use

plastic to biodegradable, compostable or recyclable

alternatives,according to research byenvironmental

thinktankGreenAlliance.Butcouldthesequickfixes

cause further harm to the environment? We talk to

MarkMiodownik, a materialsscientistwho’sleading

theBigCompostExperiment.Thisnationwidecitizen

science experiment will explore whether home-

compostable plastics really do compost in your garden.

HOWDOYOUMAKEBIODEGRADABLEPLASTICS?

Plasticsaremadeoflong-chaincarbonmolecules,and

so polythene, for instance, is lots of little ethylene

moleculeslinkedup,andtheycreatethissortofplastic

bagmaterialwhichis strong,toughandlight.

It turnsoutthatmostoflifealsoinvolveslong-chain

carbonmolecules,soyoucangetthesestructuresfrom

things like corn and starch and so, you basically

harvest a crop, use that as your carbon source, and

createpolymersbasedonthose.Thesepolymerswork

thesameastheoneswederivefrompetrochemicals.

Butyoucangoonestagefurtherandyoucanmake

themsortoftastytomicroorganisms,solittlebacteria

willeat them, andthen this is where biodegradable

plastics come from.

HOWSHOULDWEDISPOSE OF BIODEGRADABLE AND

COMPOSTABLEPL ASTIC?

There’sa slightproblemwithit at themoment.Inorder

to getthe properties that we needfrom plastics, for

themtolastsixmonthsora yearprotectingyourfood,

youwantit tolasta longtimewithoutit beingeatenby

bugs.Otherwise,foodwouldgooffinyourcupboard.

Andyou’vegot toremember,theseplastics needto

survivehumidandhotenvironments. Andso,inorder

togettheplasticstobeasgoodasthat,youoftenhaveto

dothings chemicallyto them.That makesthem less

easy for bugs to eat, and that means that their

biodegradabilityrequirescertainconditions.

So,mostbiodegradablepolymerswillonlybiodegrade

at temperaturesof 50°C or60°C, forinstance, in the

particularconditionsofanindustrialcomposter.You

might get something like a biodegradable wipe, and it

“Mostbiodegradablepolymerswillonly

biodegradeattemperaturesof50°Cor60°C,inthe

particular conditions of an industrial composter”

ABOVEThis

recycled

plasticina

factorycan

havea new

leaseoflife

overandover

again.Mark

Miodownik

saysthat

moreeffort

shouldbe

madeto

ensureall

plasticsare

recyclable,

ratherthan

creating

compostable

versions

saysbiodegradableonit,butunlessyouputthatthingin

anindustrialcomposterattherighttemperatureandthe

righthumiditywiththerightbugs,it willnotbiodegrade.

It willstillbeintheenvironmenta yearlater;if youputit

inthesea,it willbethereforyears. So, you really should

put it in the general waste bin.

WHAT’SBETTER:BIODEGRADINGORRECYCLING?

If youhavea recyclableplastic,thenyouknowwhereto

putit:youputit intherecycling.Wehavesystemsinplace.

Andthegoodthinghereisthatyou’rehangingontothe

carbon.Butinthecaseofa biodegradableplastic,having

gotit froma crop,if youjustbiodegradeit inanindustrial

composterthenpotentiallyyou’reputtingthecarbonback

in the atmosphere. What we really want to do is keep

carboninthesystem,becauseweasweknow,we’retrying

togetridofcarbondioxideoutoftheatmosphere.Wewant

everything to be recyclable, and we want to recycle it.

IS THERE ANY VALUE IN SWAPPING SINGLE-USE PLASTIC

FOR THESE ‘BIODEGRADABLE’ MATERIALS THAT DON’T

BIODEGRADEANDCAN’TBERECYCLED?

I thinkthereisn’tanyvalueatthemoment,becausethere

isn’tanysuchthingasa sustainablematerial.Paper’snot

sustainable,steelis notsustainable,glassis notsustainable.

Things are not sustainable in their own right. Onlya 2

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