Ukusetyenziswa kunye nemisebenzi yezinto ezisisiseko zeplastiki

Ukusetyenziswa kunye nemisebenzi yezinto ezisisiseko zeplastiki

iplastiki

1. Sebenzisa ulwahlulo

Ngokutsho kweempawu ezahlukeneyo zokusetyenziswa kweeplastiki ezahlukeneyo, iiplastiki zihlala zihlulwe zibe ziindidi ezintathu: iiplastiki eziqhelekileyo, iiplastiki zobunjineli kunye neeplastiki ezikhethekileyo.

① Iplastiki eqhelekileyo

Ngokubanzi ibhekisa kwiiplastiki ezinemveliso enkulu, ukusetyenziswa okubanzi, ukwakheka okuhle kunye nexabiso eliphantsi.Kukho iintlobo ezintlanu zeeplastiki eziqhelekileyo, ezizezi i-polyethylene (PE), i-polypropylene (PP), i-polyvinyl chloride (PVC), i-polystyrene (PS) kunye ne-acrylonitrile-butadiene-styrene copolymer (ABS).Ezi ntlobo zintlanu zeeplastiki zenza uninzi lwezixhobo zeplastiki eziluhlaza, kwaye ezinye zinokuthi zihlelwe kwiintlobo zeplastiki ezikhethekileyo, ezifana ne: PPS, PPO, PA, PC, POM, njl., zisetyenziswa kwiimveliso zobomi bemihla ngemihla. incinci kakhulu, ubukhulu becala Isetyenziswa kwimimandla ephezulu efana neshishini lobunjineli kunye nobuchwepheshe bokhuselo lwesizwe, njengeemoto, i-aerospace, ulwakhiwo, kunye nonxibelelwano.Ngokohlelo lweplastiki, iiplastiki zinokwahlulwa zibe yi-thermoplastics kunye ne-thermosetting plastics.Kwiimeko eziqhelekileyo, iimveliso ze-thermoplastic zinokuphinda zisetyenziswe, ngelixa iiplastiki ze-thermosetting azikwazi.Ngokweempawu ezibonakalayo zeeplastiki, zinokwahlulwa zibe yimathiriyeli ecacileyo, eguquguqukayo kunye ne-opaque, njenge-PS, i-PMMA, i-AS, i-PC, njl njl. iiplastiki ezicacileyo , Kwaye ininzi yezinye iiplastiki ziyi-opaque.

Iipropati kunye nokusetyenziswa kweeplastiki ezisetyenziswa ngokuqhelekileyo:

1. Polyethylene:

I-polyethylene esetyenziswa ngokuqhelekileyo ingahlulwa ibe yi-polyethylene ephantsi (i-LDPE), i-polyethylene ephezulu (i-HDPE) kunye ne-linear low density polyethylene (LLDPE).Phakathi kwezi zintathu, i-HDPE inezixhobo ezingcono zokushisa, zombane kunye nemishini, ngelixa i-LDPE kunye ne-LLDPE zinokuguquguquka okungcono, iimpawu zempembelelo, iipropati zokwenza ifilimu, njl. , ngelixa i-HDPE inoluhlu olubanzi lwezicelo, ezifana neefilimu, iipayipi, kunye neenaliti ezifunekayo imihla ngemihla.

2. Polypropylene:

Ngokwentelekiso, i-polypropylene ineentlobo ezininzi, ukusetyenziswa okuntsokothileyo, kunye noluhlu olubanzi lwamasimi.Iindidi ikakhulu ziquka i-homopolymer polypropylene (homopp), ibhloko ye-polymer polypropylene (copp) kunye ne-random copolymer polypropylene (rapp).Ngokwesicelo i-Homopolymerization isetyenziswa kakhulu kwimimandla yomzobo wecingo, ifayibha, inaliti, ifilimu yeBOPP, njl. njl. Ipolymer polypropylene isetyenziswa ikakhulu kwizixhobo zendlu yokutofa iindawo, izinto ezilungiswayo, iimveliso zokutofa imihla ngemihla, imibhobho, njl. i-polypropylene isetyenziswa kakhulu kwiiMveliso ezicacileyo, iimveliso eziphezulu, iibhobho eziphezulu zokusebenza, njl.

3. Polyvinyl chloride:

Ngenxa yexabiso eliphantsi kunye nezakhiwo zokuzibamba umlilo, unoluhlu olubanzi lokusetyenziswa kwintsimi yokwakha, ngokukodwa kwimibhobho yogutyulo, iingcango zentsimbi yeplastiki kunye neefestile, iipleyiti, isikhumba sokufakelwa, njl.

4. Ipolystyrene:

Njengohlobo lwezinto ezibonakalayo eziluhlaza, xa kukho imfuneko yokungafihli, inoluhlu olubanzi lokusetyenziswa, njengezibane zeemoto, iindawo ezicacileyo zemihla ngemihla, iikomityi ezicacileyo, iinkonkxa, njl.

5. ABS:

Yiplastiki yobunjineli esebenza ngeendlela ezininzi eneempawu ezibalaseleyo zoomatshini kunye nezobushushu.Isetyenziswa ngokubanzi kwizixhobo zendlu, iipaneli, iimaski, iindibano, izixhobo, njl., ngakumbi izixhobo zasekhaya, ezifana noomatshini bokuhlamba, i-air conditioners, iifriji, iifeni zombane, njl. ukuguqulwa kweplastiki.

②Iiplastiki zobunjineli

Ngokuqhelekileyo ibhekisela kwiiplastiki ezinokumelana namandla athile angaphandle, zibe nezixhobo ezifanelekileyo zemishini, ukuxhathisa ubushushu obuphezulu kunye obuphantsi, kwaye zibe nokuzinza okuhle kwe-dimensional, kwaye zinokusetyenziswa njengezakhiwo zobunjineli, ezifana ne-polyamide kunye ne-polysulfone.Kwiiplastiki zobunjineli, zohlulwe zibe ziindidi ezimbini: iiplastiki zobunjineli ngokubanzi kunye neeplastiki ezikhethekileyo zobunjineli.Iiplastiki zobunjineli zinokuhlangabezana neemfuno eziphezulu ngokweempawu zoomatshini, ukuqina, ukuxhathisa umhlwa, kunye nokumelana nobushushu, kwaye zikulungele ngakumbi ukusetyenzwa kwaye zinokuthatha indawo yezixhobo zetsimbi.Iiplastiki zobunjineli zisetyenziswa kakhulu kumbane kunye ne-elektroniki, iimoto, ulwakhiwo, izixhobo zeofisi, oomatshini, i-aerospace kunye namanye amashishini.Ukufaka iplastiki endaweni yentsimbi kunye neplastiki kwiplanga kuye kwaba yinto yamazwe ngamazwe.

Iiplastiki zobunjineli ngokubanzi ziquka: i-polyamide, i-polyoxymethylene, i-polycarbonate, i-polyphenylene ether elungisiweyo, i-thermoplastic polyester, i-ultra-high molecular weight polyethylene, i-methylpentene polymer, i-vinyl alcohol copolymer, njl.

Iiplastiki zobunjineli ezikhethekileyo zohlulwe zibe ziintlobo eziqhagamshelweyo nezingadityaniswanga.Iindidi ezidityanisiweyo ezinqamlezileyo zezi: i-polyamino bismaleamide, i-polytriazine, i-polyimide edibeneyo, i-epoxy resin ekwazi ukumelana nobushushu kunye nokunye.Iindidi ezingenayo i-crosslinked zezi: i-polysulfone, i-polyethersulfone, i-polyphenylene sulfide, i-polyimide, i-polyether ether ketone (i-PEEK) njalo njalo.

③Iiplastiki ezikhethekileyo

Ngokuqhelekileyo ibhekisela kwiiplastiki ezinemisebenzi ekhethekileyo kwaye zinokusetyenziswa kwizicelo ezikhethekileyo ezifana nokuhamba ngeenqwelomoya kunye ne-aerospace.Ngokomzekelo, i-fluoroplastics kunye ne-silicones inokumelana nobushushu obuphezulu, i-self-lubricating kunye neminye imisebenzi ekhethekileyo, kunye neeplastiki eziqiniweyo kunye neeplastiki ezinogwebu zineempawu ezikhethekileyo ezifana namandla aphezulu kunye nokunyuka okuphezulu.Ezi plastiki zezodidi lweeplastiki ezikhethekileyo.

a.Iplastiki eyomeleziweyo:

Izixhobo zeplastiki ezomeleziweyo zinokwahlulwa zibe yigranular (njengeplastiki ye-calcium eyomeleziweyo), ifayibha (efana nefayibha yeglasi okanye ilaphu leglasi elomeleziweyo), kunye neflake (efana ne-mica eyomeleziweyo yeplastiki) ngembonakalo.Ngokwemathiriyeli, inokwahlulwa ibe yiplastiki eqinisiweyo esekwe kwilaphu (njengeragi eqinisiweyo okanye i-asbestos eyomeleziweyo), iiplastiki ezizaliswe ngamaminerali angeyonxalenye (ezifana nequartz okanye iiplastiki ezizaliswe yimica), kunye neeplastiki eziqiniswe ngefayibha (ezifana necarbon fibre eqinisiweyo). iiplastiki).

b.Ugwebu:

Iiplastiki ezinogwebu zinokwahlulwa zibe ziindidi ezintathu: ugwebu oluqinileyo, olungagungqiyo kunye noluguquguqukayo.I-foam eqinile ayinakuguquguquka, kwaye ukuqina kwayo koxinzelelo kukhulu kakhulu.Iyakukhubaza kuphela xa ifikelela kwixabiso elithile loxinzelelo kwaye ayikwazi ukubuyela kwimeko yayo yangaphambili emva kokuba uxinzelelo luphelile.I-foam ethambileyo iyabhetyebhetye, inobulukhuni obuphantsi bokucinezelwa, kwaye kulula ukuyikhubaza.Buyisela imeko yokuqala, i-deformation eseleyo incinci;ukuguquguquka kunye nezinye iimpawu ze-foam e-semi-rigid ziphakathi kwee-foam eziqinileyo kunye nezithambileyo.

Eyesibini, ulwahlulo lomzimba kunye neekhemikhali

Ngokweempawu ezahlukeneyo zomzimba kunye neekhemikhali zeeplastiki ezahlukeneyo, iiplastiki zinokwahlulwa zibe ziindidi ezimbini: iiplastiki ze-thermosetting kunye neeplastiki ze-thermoplastic.

(1) Thermoplastic

I-Thermoplastics (i-Thermo plastics): ibhekisela kwiiplastiki eziya kunyibilika emva kokufudumeza, zinokungena kwi-mold emva kokupholisa, kwaye emva koko zinyibilike emva kokufudumeza;ukufudumeza kunye nokupholisa kungasetyenziselwa ukuvelisa utshintsho olubuyiselwa umva (ulwelo ←→oluqilima), ewe Okubizwa ngokuba lutshintsho lomzimba.I-thermoplastics yenjongo ngokubanzi inamaqondo obushushu okusetyenziswa rhoqo angaphantsi kwe-100°C.I-Polyethylene, i-polyvinyl chloride, i-polypropylene, kunye ne-polystyrene zikwabizwa ngokuba ziiplastiki ezine zenjongo jikelele.Iiplastiki ze-Thermoplastic zihlulwe zibe yi-hydrocarbons, i-vinyls kunye ne-polar genes, ubunjineli, i-cellulose kunye nezinye iintlobo.Iyathambile xa ishushu, kwaye iba lukhuni xa ipholile.Inokuthanjiswa ngokuphindaphindiweyo kwaye iqiniswe kwaye igcine imilo ethile.Iyanyibilika kwizinyibilikisi ezithile kwaye inepropathi yokunyibilika kunye nokunyibilika.I-Thermoplastics ine-insulation yombane egqwesileyo, ngakumbi i-polytetrafluoroethylene (PTFE), i-polystyrene (PS), i-polyethylene (PE), i-polypropylene (PP) ine-dielectric ephantsi kakhulu kunye nelahleko ye-dielectric.Kwizixhobo zokugquma okuphezulu kunye nokufakwa kwamandla ombane aphezulu.I-Thermoplastics kulula ukuyibumba kunye nokusebenza, kodwa inokumelana nokushisa okuphantsi kwaye kulula ukukhwela.Iqondo lokurhubuluza liyahluka ngomthwalo, ubushushu bendalo esingqongileyo, isinyibilikisi, kunye nokufuma.Ukuze unqobe obu buthathaka be-thermoplastics kwaye uhlangabezane neemfuno zezicelo kwiinkalo zobuchwepheshe bendawo kunye nophuhliso lwamandla amatsha, onke amazwe aphuhlisa i-resins enganyangekiyo yokushisa enokuthi inyibilike, njenge-polyether ether ketone (PEEK) kunye ne-polyether sulfone ( PES)., I-Polyarylsulfone (PASU), i-polyphenylene sulfide (i-PPS), njl. Izinto ezihlanganisiweyo ezizisebenzisayo njengee-resin ze-matrix zineempawu eziphezulu zemishini kunye nokumelana neekhemikhali, zinokuthi zibe ne-thermoformed kunye ne-welded, kwaye zibe namandla angcono e-interlaminar shear kune-epoxy resins.Ngokomzekelo, ukusebenzisa i-polyether ether ketone njenge-matrix resin kunye ne-carbon fiber ukwenza izinto ezidibeneyo, ukumelana nokukhathala kudlula i-epoxy / carbon fiber.Inokumelana neempembelelo ezilungileyo, ukuxhathisa okulungileyo kokunyuka kwiqondo lobushushu begumbi, kunye nokuqhubekeka kakuhle.Ingasetyenziswa ngokuqhubekayo kwi-240-270 ° C.Yimathiriyeli efanelekileyo yobushushu obuphezulu.Izinto ezidibeneyo ezenziwe nge-polyethersulfone njenge-matrix resin kunye ne-carbon fiber inamandla amakhulu kunye nobunzima kwi-200 ° C, kwaye inokugcina ukuchasana kwempembelelo enhle kwi -100 ° C;ayinayo ityhefu, ayinakutsha, umsi omncinci, kunye nokumelana nemitha.Ewe, kulindeleke ukuba isetyenziswe njengenxalenye ephambili yesiphekepheke, kwaye inokubunjwa ibe yiradome, njl.

Iiplastiki ze-formaldehyde ezinqamlekileyo ziquka iiplastiki ze-phenolic, iiplastiki ze-amino (ezifana ne-urea-formaldehyde-melamine-formaldehyde, njl.).Ezinye iiplastiki ezidityaniswe ngomnqamlezo ziquka i-polyester ezingaxutywanga, iireyini ze-epoxy, kunye ne-phthalic diallyl resins.

(2) Iplastiki ye-thermosetting

Iiplastiki zeThermosetting zibhekisela kwiiplastiki ezinokunyangwa phantsi kobushushu okanye ezinye iimeko okanye zibe neempawu ezinganyibilikiyo (ezinyibilikayo), ezifana neeplastiki zephenolic, iiplastiki ze-epoxy, njl.Emva kokucutshungulwa kwe-thermal kunye nokubunjwa, imveliso ephilileyo engabonakaliyo kunye ne-insoluble yenziwa, kwaye iamolekyu ze-resin zidibaniswe kwisakhiwo sothungelwano ngesakhiwo somgca.Ubushushu obuninzi buya kubola kwaye butshabalalise.Iiplastiki eziqhelekileyo ze-thermosetting ziquka i-phenolic, i-epoxy, i-amino, i-polyester engaxutywanga, i-furan, i-polysiloxane kunye nezinye izinto, kunye ne-polydipropylene phthalate entsha.Zinenzuzo yokumelana nokushisa okuphezulu kunye nokuchasana nokuguqulwa xa kushushu.Ukungalungi kukuba amandla omatshini ngokuqhelekileyo akaphezulu, kodwa amandla omatshini angaphuculwa ngokufaka iifayili ukwenza izinto ezixutywe okanye izinto ezibunjiweyo.

Iiplastiki ze-Thermosetting ezenziwe nge-phenolic resin njengeyona nto iphambili ekrwada, efana ne-phenolic mold plastic (eyaziwa ngokuba yi-Bakelite), ihlala ixesha elide, i-dimensionally stable, kwaye iyaxhathisa kwezinye izinto zekhemikhali ngaphandle kweealkalis ezinamandla.Iifayile ezahlukeneyo kunye nezongezelelo zinokongezwa ngokweendlela ezahlukeneyo zokusetyenziswa kunye neemfuno.Kwiintlobo ezifuna ukusebenza okuphezulu kwe-insulation, i-mica okanye i-fiber yeglasi ingasetyenziswa njenge-filler;kwiindidi ezifuna ukumelana nobushushu, i-asbestos okanye ezinye iifayili ezikwazi ukumelana nobushushu zingasetyenziswa;kwiindidi ezifuna ukuxhathisa kwe-seismic, iifayibha ezahlukeneyo ezifanelekileyo okanye irabha zingasetyenziswa njengezizalisi Kwaye ezinye ii-agent eziqinisayo zokwenza izinto ezinobunzima obuphezulu.Ukongezelela, i-phenolic resins eguqulwayo njenge-aniline, i-epoxy, i-polyvinyl chloride, i-polyamide, kunye ne-acetal ye-polyvinyl nayo ingasetyenziselwa ukuhlangabezana neemfuno zezicelo ezahlukeneyo.I-Phenolic resins ingasetyenziselwa ukwenza i-phenolic laminates, ebonakaliswe ngamandla amakhulu omatshini, iipropati ezilungileyo zombane, ukuxhathisa ukubola, kunye nokulungiswa okulula.Zisetyenziswa ngokubanzi kwizixhobo zombane ezisezantsi.

Aminoplasts ziquka urea formaldehyde, melamine formaldehyde, urea melamine formaldehyde njalo njalo.Zineenzuzo zokuthungwa okunzima, ukuxhathisa ukukrazula, ukungabikho mbala, ukuguquguquka, njl njl. Ukongeza izinto zombala zingenziwa kwiimveliso ezinemibala, eyaziwa ngokuba yi-jade yombane.Ngenxa yokuba iyamelana neoli kwaye ayichatshazelwa yi-alkalis ebuthathaka kunye ne-solvents eziphilayo (kodwa i-asidi i-asidi), ingasetyenziselwa kwi-70 ° C ixesha elide, kwaye inokumelana ne-110 ukuya kwi-120 ° C kwixesha elifutshane, kwaye iyakwazi zisetyenziswe kwiimveliso zombane.Iplastiki yeMelamine-formaldehyde inobunzima obuphezulu kuneplastiki ye-urea-formaldehyde, kwaye inokuxhathisa okungcono kwamanzi, ukumelana nobushushu, kunye nokuxhathisa i-arc.Ingasetyenziswa njenge-arc-resistant insulating material.

Kukho iintlobo ezininzi zeeplastiki ze-thermosetting ezenziwe nge-epoxy resin njengeyona nto iphambili ekrwada, phakathi kwayo malunga ne-90% isekelwe kwi-bisphenol A epoxy resin.Inonamathela ngokugqwesileyo, ukugquma kombane, ukumelana nobushushu kunye nokuzinza kweekhemikhali, i-shrinkage ephantsi kunye nokufunxa kwamanzi, kunye namandla afanelekileyo omatshini.

Zombini i-polyester engafakwanga kunye ne-epoxy resin inokwenziwa kwi-FRP, enamandla agqwesileyo ngoomatshini.Ngokomzekelo, i-fiber yeglasi eyomeleziweyo yeplastiki eyenziwe nge-polyester engaxutywanga ineempawu ezintle zoomatshini kunye noxinano oluphantsi (kuphela i-1/5 ukuya kwi-1/4 yentsimbi, i-1/2 ye-aluminium), kwaye kulula ukuqhutyelwa kwiindawo ezahlukeneyo zombane.Iimpawu zombane kunye nezomatshini zeplastiki ezenziwe nge-dipropylene phthalate resin zingcono kunezo ze-phenolic kunye neeplastiki ze-amino thermosetting.Ine-hygroscopicity ephantsi, ubungakanani bemveliso obuzinzile, ukusebenza kakuhle kokubumba, ukuxhathisa kwe-asidi kunye ne-alkali, amanzi abilayo kunye nezinye izinyibilikisi eziphilayo.I-compound yokubumba ifanelekile kumacandelo okuvelisa kunye nesakhiwo esiyinkimbinkimbi, ukumelana nokushisa kunye nokunyuka okuphezulu.Ngokuqhelekileyo, inokusetyenziswa ixesha elide kuluhlu lweqondo lokushisa -60 ~ 180℃, kwaye ibakala lokumelana nobushushu linokufikelela ku-F ukuya kwibakala le-H, eliphakamileyo kunokumelana nobushushu be-phenolic kunye neeplastiki ze-amino.

Iiplastiki ze-silicone ngendlela yesakhiwo se-polysiloxane zisetyenziswa ngokubanzi kwi-electronics kunye neteknoloji yombane.Iiplastiki ezilaminethiweyo zeSilicone ziqiniswa kakhulu ngelaphu leglasi;iiplastiki ezibunjiweyo ze-silicone zigcwele ubukhulu becala ngefiber yeglasi kunye neasbestos, ezisetyenziselwa ukwenza iindawo ezikwaziyo ukumelana nobushushu obuphezulu, amaza omoya aphezulu okanye iimotor eziphantsi kwamanzi, izixhobo zombane, kunye nezixhobo zombane.Olu hlobo lweplastiki lubonakaliswe ngexabiso eliphantsi le-dielectric kunye nexabiso le-tgδ, kwaye alichatshazelwa kancinci ngokuphindaphindiweyo.Isetyenziswa kumashishini ombane kunye ne-elektroniki ukuxhathisa i-corona kunye ne-arcs.Nangona ukukhutshwa kubangela ukubola, imveliso yi-silicon dioxide endaweni ye-carbon conductive emnyama..Olu hlobo lwemathiriyeli lunamandla okumelana nobushushu kwaye lunokusetyenziswa ngokuqhubekayo kwi-250 ° C.Izinto ezingalunganga eziphambili zepolysilicone zinamandla aphantsi omatshini, ukunamathela okuncinci kunye nokunganyangeki kweoli.Iipolymers ezininzi ze-silicone ezilungisiweyo ziye zaphuhliswa, ezifana neeplastiki ze-silicone ezilungisiweyo ze-polyester kwaye zisetyenziswe kwiteknoloji yombane.Ezinye iiplastikhi zombini ziplastiki ze-thermoplastic kunye ne-thermosetting.Ngokomzekelo, i-polyvinyl chloride ngokuqhelekileyo i-thermoplastic.I-Japan iphuhlise uhlobo olutsha lwe-polyvinyl chloride engamanzi eyi-thermoset kwaye inobushushu bokubumba obuyi-60 ukuya kwi-140°C.Iplastiki ebizwa ngokuba yiLundex eUnited States inazo zombini iiMpawu zokusetyenzwa kwe-thermoplastic, kunye neempawu ezibonakalayo zeeplastiki ze-thermosetting.

① Iiplastiki zeHydrocarbon.

Yiplastiki engeyiyo i-polar, eyahlulahlulwe ibe yikristale kunye ne-non-crystalline.Iiplastiki ze-crystalline hydrocarbon zibandakanya i-polyethylene, i-polypropylene, njl., kunye neeplastiki ze-hydrocarbon ezingena-crystalline ziquka i-polystyrene, njl.

②Iiplastiki zeVinyl ezinemizila yendalo emhlophe.

Ngaphandle kwe-fluoroplastics, uninzi lwazo aluyi-crystalline imizimba ebonakalayo, kuquka i-polyvinyl chloride, i-polytetrafluoroethylene, i-acetate ye-polyvinyl, njl. Uninzi lwe-vinyl monomers lunokwenziwa i-polymerized nge-catalysts radical.

③Iiplastiki zobunjineli zeThermoplastic.

Ikakhulu ibandakanya i-polyoxymethylene, i-polyamide, i-polycarbonate, i-ABS, i-polyphenylene ether, i-polyethylene terephthalate, i-polysulfone, i-polyethersulfone, i-polyimide, i-polyphenylene sulfide, njl. Polytetrafluoroethylene.I-polypropylene elungisiweyo, njl njl.

④ Iiplastiki zeselulosi zeThermoplastic.

Ikakhulu ibandakanya i-cellulose acetate, i-cellulose acetate butyrate, i-cellophane, i-cellophane kunye nokunye.

Singasebenzisa zonke izinto zeplastiki ezingentla.
Kwiimeko eziqhelekileyo, i-PP yokutya kunye ne-medical-grade PP isetyenziselwa iimveliso ezifanayoamacephe. Ipipetteyenziwe ngezinto HDPE, kunyeityubhu yokuvavanyayenziwe ngokubanzi ngebakala lezonyango PP okanye PS izinto.Siseneemveliso ezininzi, sisebenzisa izinto ezahlukeneyo, kuba singundoumenzi, phantse zonke iimveliso zeplastiki zinokuveliswa


Ixesha lokuposa: May-12-2021