raug rau ultraviolet hluav taws xob
Kev raug rau lub hnub ultraviolet hluav taws xob tuaj yeem degrade yas nyob rau lub sijhawm. Polymer photodegradation tshwm sim thaum pom tsis pom cov hluav taws xob ultraviolet uas muaj cov luv luv wavelengths tawg polymer chains hauv cov yas. Qhov no yog hu ua txheej txheem photodegradation. Nws yog tshwm sim los ntawm kev raug ultraviolet hluav taws xob thiab ua rau txo qis hauv lub cev. Cov no suav nrog kev poob ntawm kev cuam tshuam lub zog, hloov xim, tawg, poob ntawm elongation thiab tensile zog, thiab nto chalking. Piv txwv li, photodegradation tshwm sim los ntawm UV hluav taws xob tuaj yeem ua rau cov rooj zaum hauv vaj hauv tarnish thiab ua nkig. Tsis tas li ntawd, cov xim ntawm cov rooj zaum hauv chaw ntau pob yuav tshwm chalky, thiab qee cov yas yuav txawm daj thiab tawg.
Qee yam ntxwv ntawm Ultraviolet Radiation
Ultraviolet hluav taws xob ua rau tsuas yog 4.6 feem pua ntawm hnub ci spectrum. Nws yog ntsuas nyob rau hauv nanometers (nm) thiab thaj tsam ntawm 290 mus rau 400. Txawm li cas los xij, qhov hnyav tshaj plaws ntawm UVB ntau yam yog qhov luv luv wavelengths ntawm 280 thiab 315 nanometers. Yog li ntawd, tus nqi ntawm UV hluav taws xob hluav taws xob raug (irradiation) nyob ntawm seb koj nyob qhov twg hauv ntiaj teb.
dab tsi yog irradiation
Irradiance yog tus nqi ntawm ultraviolet radiant zog tshwm sim ntawm ib qho chaw tshwj xeeb nyob rau lub sijhawm. 1Ly=1 cal/cm 2=4.184 E 4 Joule/m 2 (Ly=Langley) Yog li ntawd, rau ib xyoos ntawm kev siv sab nraum zoov tsis tu ncua hauv Sudan, lub zog xa mus rau cov khoom yas yog 220kcal / cm 2 / xyoo, thaum nyob hauv Sweden nws yog 70.
Txhua cov yas yog rhiab rau qee qhov wavelengths hauv cheeb tsam 290-400 nm UV. Yog li ntawd, polypropylene muaj peb maxima ntawm 290-300, 330 thiab 370 nm. Nylon ranges ntawm 290-315, thaum PVC homopolymer yog 320.
Degradation ntawm Polymers los ntawm UV Radiation
Polymer photodegradation tshwm sim thaum ultraviolet hluav taws xob los ntawm lub hnub yog absorbed los ntawm chemical pawg nyob rau hauv lub polymer qauv hu ua chromophores. Ib chromophore yog "ib qho atom lossis pawg ntawm cov atoms uas nws lub xub ntiag txiav txim siab xim ntawm cov khoom sib txuas". Polymer formulations yuav muaj xws li lwm yam additives xws li halogenated nplaim retardants, fillers thiab pigments. Yog li ntawd, UV stabilizers tau tsim thiab ntxiv rau cov polymers los tiv thaiv cov txheej txheem photoinitiation. Thawj peb hom yog UV absorbers, quenchers, thiab hindered amine teeb stabilizers (HALS).
1) UV absorber
Absorbers yog photostabilizers uas ua haujlwm los ntawm kev sib tw nrog chromophores kom nqus tau UV hluav taws xob. Yog li, lub absorber hloov cov teeb meem UV hluav taws xob rau hauv cov hluav taws xob tsis zoo infrared lossis cua sov uas tau tawg los ntawm polymer matrix. UV absorbers muaj qhov zoo ntawm tus nqi qis, tab sis tsuas yog tsim nyog rau lub sijhawm luv luv. UV absorbers muaj xws li:
Absorber
UV absorbers muaj qhov zoo ntawm tus nqi qis, tab sis tsuas yog tsim nyog rau lub sijhawm luv luv. UV absorbers muaj xws li:
Cov pa roj carbon dub yog ib qho zoo tshaj plaws thiab feem ntau siv UV hluav taws xob absorbers.
Lwm UV absorber yog rutile titanium oxide, uas yog siv nyob rau hauv lub 300-400 nm ntau. Txawm li cas los xij, nws tsis muaj txiaj ntsig zoo hauv qhov luv luv wavelength UVB ntau hauv qab 315.
Hydroxybenzophenone
Hydroxyphenyl benzotriazole kuj yog ib tug paub zoo UV stabilizer nrog rau qhov zoo ntawm kev tsim nyog rau nruab nrab los yog ntshiab daim ntaub ntawv. Hydroxyphenylbenzotriazoles tsis muaj txiaj ntsig zoo hauv cov khoom me me hauv qab 100 microns.
Benzophenone rau PVC
Anzotriazoles thiab hydroxyphenyltriazines rau polycarbonates.
Oxalanilide rau polyamides
2) Quencher
Quenchers rov qab lub xeev zoo siab ntawm chromophore mus rau hauv av xeev los ntawm kev hloov lub zog. Cov neeg ua haujlwm hloov hluav taws xob ua los ntawm quenching lub xeev zoo siab ntawm carbonyl pawg tsim thaum lub sij hawm photooxidation ntawm cov ntaub ntawv yas thiab decomposition ntawm hydroperoxides. Qhov no tiv thaiv kev tawg ntawm daim ntawv cog lus thiab thaum kawg tsim cov dawb radicals.
Nickel quenching tus neeg sawv cev
Nickel quencher yog hom feem ntau siv hauv kev ua yeeb yaj kiab ua liaj ua teb. Cov no tsis tau siv dav vim tias lawv muaj cov hlau hnyav thiab muab cov khoom kawg rau cov xim daj lossis ntsuab. Txawm li cas los xij, zoo li cov hindered amine teeb stabilizers tau tham hauv qab no, nickel quenchers tsis zoo rau stabilizing UV hluav taws xob.
3) Hindered Amine Lub Teeb Stabilizer (HALS)
HALS yog cov khoom siv hluav taws xob ntev ntev uas ua haujlwm los ntawm kev ntes cov dawb radicals tsim thaum lub sij hawm photooxidation ntawm cov ntaub ntawv yas. HALS yog li txwv cov txheej txheem photodegradation. Lub peev xwm ntawm HALS kom tshem tawm cov dawb radicals tshwm sim los ntawm kev nqus ntawm UV hluav taws xob tuaj yeem piav qhia los ntawm kev tsim cov pab pawg nitroxyl hauv cov txheej txheem hu ua Denisov voj voog.
Txawm hais tias cov khoom lag luam muaj HALS sib txawv hauv cov qauv, lawv txhua tus muaj 2,2,6,6-tetramethylpiperidine nplhaib qauv. HALS yog qee qhov ua tau zoo tshaj plaws UV hluav taws xob stabilizers.
UV Stabilizers rau ntau yam yas
Piv txwv li, HALS tau pab txhawb kev tsim cov polypropylene hauv kev lag luam tsheb. Thaum HALS tseem siv tau zoo heev hauv polyolefins, polyethylene thiab polyurethane, lawv tsis tuaj yeem siv los ua cov stabilizers rau UV hluav taws xob hauv PVC.
Kev sib xyaw ntawm UV Stabilizers
Txij li thaum tag nrho peb lub luag haujlwm ua haujlwm los ntawm cov txheej txheem sib txawv, lawv feem ntau ua ke rau hauv kev sib koom ua ke ntawm UV hluav taws xob absorbing additives. Piv txwv li, benzotriazoles feem ntau siv ua ke nrog HALS los tiv thaiv fading thiab discoloration hauv cov xim xim.
