Polyester yog cov khoom siv hluavtaws tseem ceeb, nrog rau cov kauj ruam tseem ceeb hauv nws cov txheej txheem tsim khoom yog cov tshuaj tiv thaiv polycondensation. Polycondensation yog ib txoj kev uas monomer molecules reacts tsim polymers thiab me me molecule by-products (feem ntau yog dej los yog methanol). Rau cov synthesis ntawm polyester, feem ntau monomers yog terephthalic acid (PTA) los yog dimethyl terephthalate (DMT) thiab ethylene glycol (EG).
Cov kauj ruam daws teeb meem:
- Transesterification Reaction(yog siv DMT): Ua ntej, DMT reacts nrog ethylene glycol nyob rau hauv ib tug transesterification cov tshuaj tiv thaiv los tsim cov monomer bis (hydroxyethyl) terephthalate (BHET) thiab methanol. Cov tshuaj tiv thaiv no feem ntau tshwm sim ntawm 200-250 degree thiab yuav tsum muaj cov catalyst (xws li antimony compounds).
- Polycondensation Reaction: Tom ntej no, BHET tau dhau los ua polycondensation ntxiv los ua cov saw ntev poly (ethylene terephthalate) (PET) thiab dej raws li cov khoom lag luam. Cov tshuaj tiv thaiv no feem ntau tshwm sim ntawm qhov kub siab ntawm 250-280 degree thiab nyob rau hauv lub tshuab nqus tsev lossis cov pa cua tsis zoo kom tshem tawm cov dej uas tsim tawm, tsav cov tshuaj tiv thaiv rau cov khoom hnyav dua molecular polymers.
Reaction Mechanism:
Nyob rau hauv cov tshuaj tiv thaiv polycondensation, hydroxyl (-OH) thiab carboxyl (-COOH) los yog ester (-COOR) pawg ua rau lub cev qhuav dej lossis cawv tshem tawm cov tshuaj tiv thaiv los tsim cov ester bonds (-COO-). Thaum lub sijhawm ua haujlwm no, cov monomers maj mam txuas mus rau hauv cov saw hlau, tsim cov linear polymers.
Reaction Control:
Kev tswj cov tshuaj tiv thaiv polycondensation yog qhov tseem ceeb rau cov khoom ntawm cov khoom kawg. Cov tshuaj tiv thaiv kub, lub sij hawm, tus nqi catalyst, thiab tej yam kev mob (xws li lub tshuab nqus tsev lossis nitrogen ntws) tag nrho cuam tshuam rau qhov hnyav molecular thiab lub cev lub cev ntawm polyester. Piv txwv li, cov tshuaj tiv thaiv siab dua thiab lub sij hawm ntev dua cov tshuaj tiv thaiv pab tsim cov khoom hnyav dua molecular polyester tab sis kuj tseem tuaj yeem ua rau degradation thiab sab cuam tshuam.
Kev Siv Hluav Taws Xob:
Los ntawm kev tswj cov tshuaj tiv thaiv polycondensation, cov ntaub ntawv polyester nrog cov khoom sib txawv tuaj yeem tsim ua kom tau raws li ntau yam kev xav tau. Piv txwv li, siab molecular hnyav polyester feem ntau yog siv rau cov khoom uas yuav tsum tau muaj zog thiab toughness, xws li lub raj mis yas thiab engineering yas, thaum uas tsis muaj molecular hnyav polyester yog siv los ua fibers thiab films.
