Qhov hu uapolyurethaneyog lub npe luv ntawm polyurethane, uas yog tsim los ntawm cov tshuaj tiv thaiv ntawm polyisocyanates thiab polyols, thiab muaj ntau pawg amino ester rov ua dua (- NH-CO-O -) ntawm cov saw molecular. Hauv cov polyurethane resins synthesized tiag tiag, ntxiv rau pawg amino ester, kuj muaj cov pab pawg xws li urea thiab biuret. Polyols koom nrog cov saw ntev nrog cov pab pawg hydroxyl thaum kawg, uas hu ua "cov saw mos mos", thaum polyisocyanates hu ua "cov saw nyuaj".
Ntawm cov polyurethane resins uas tsim los ntawm cov saw hlau mos thiab tawv, tsuas yog ib feem me me xwb yog cov amino acid esters, yog li nws yuav tsis tsim nyog hu lawv ua polyurethane. Hauv kev nkag siab dav dav, polyurethane yog ib qho khoom ntxiv ntawm isocyanate.
Cov isocyanates sib txawv sib xyaw ua ke nrog cov tshuaj polyhydroxy los tsim ntau yam qauv ntawm polyurethane, yog li tau txais cov ntaub ntawv polymer nrog cov khoom sib txawv, xws li plastics, roj hmab, coatings, fibers, adhesives, thiab lwm yam. Polyurethane roj hmab
Cov roj hmab polyurethane yog ib hom roj hmab tshwj xeeb, uas yog ua los ntawm kev sib xyaw polyether lossis polyester nrog isocyanate. Muaj ntau hom vim muaj ntau hom khoom siv raw, cov xwm txheej sib xyaw, thiab cov txheej txheem sib txuas. Los ntawm kev pom ntawm cov qauv tshuaj lom neeg, muaj cov hom polyester thiab polyether, thiab los ntawm kev pom ntawm txoj kev ua tiav, muaj peb hom: hom sib xyaw, hom casting, thiab hom thermoplastic.
Cov roj hmab polyurethane ua los ntawm cov khoom siv feem ntau yog ua los ntawm kev sib xyaw cov polyester linear lossis polyether nrog diisocyanate los tsim cov prepolymer uas muaj qhov hnyav molecular qis, uas tom qab ntawd raug rau cov tshuaj tiv thaiv txuas ntxiv kom tsim tau cov polymer uas muaj qhov hnyav molecular siab. Tom qab ntawd, cov neeg sawv cev sib txuas uas tsim nyog raug ntxiv thiab cua sov kom kho nws, ua cov roj hmab vulcanized. Txoj kev no hu ua prepolymerization lossis txoj kev ob kauj ruam.
Nws kuj tseem siv tau ib kauj ruam xwb - sib tov ncaj qha rau cov polyester lossis polyether nrog diisocyanates, cov saw hlau txuas, thiab cov neeg sawv cev sib txuas kom pib ua ib qho kev sib xyaw thiab tsim cov roj hmab polyurethane.
Qhov A-ntu hauv TPU molecules ua rau cov saw hlau macromolecular yooj yim tig, ua rau cov roj hmab polyurethane muaj qhov elasticity zoo, txo qhov softening point thiab secondary transition point ntawm cov polymer, thiab txo nws qhov hardness thiab mechanical strength. Qhov B-ntu yuav khi qhov kev tig ntawm cov saw hlau macromolecular, ua rau qhov softening point thiab secondary transition point ntawm cov polymer nce ntxiv, ua rau qhov hardness thiab mechanical strength nce ntxiv, thiab txo qhov elasticity. Los ntawm kev kho qhov molar ratio ntawm A thiab B, TPUs nrog cov khoom siv sib txawv tuaj yeem tsim tau. Cov qauv cross-linking ntawm TPU yuav tsum tsis txhob tsuas yog xav txog kev sib txuas thawj zaug, tab sis kuj tseem xav txog kev sib txuas thib ob uas tsim los ntawm hydrogen bonds ntawm cov molecules. Qhov kev sib txuas thawj zaug ntawm polyurethane txawv ntawm cov qauv vulcanization ntawm hydroxyl roj hmab. Nws cov amino ester pawg, biuret pawg, urea formate pawg thiab lwm cov pab pawg ua haujlwm tau teeb tsa hauv ib qho saw hlau tsis tu ncua thiab sib nrug, ua rau muaj cov qauv network tsis tu ncua ntawm roj hmab, uas muaj kev tiv thaiv zoo heev thiab lwm yam khoom zoo heev. Qhov thib ob, vim muaj ntau pawg ua haujlwm sib koom ua ke xws li urea lossis carbamate pawg hauv polyurethane roj hmab, hydrogen bonds tsim ntawm cov saw hlau molecular muaj zog siab, thiab cov crosslinking bonds thib ob tsim los ntawm hydrogen bonds kuj muaj kev cuam tshuam loj rau cov khoom ntawm polyurethane roj hmab. Secondary cross-linking ua rau polyurethane roj hmab muaj cov yam ntxwv ntawm thermosetting elastomers ntawm ib sab tes, thiab ntawm qhov tod tes, qhov cross-linking no tsis yog cross-linked tiag tiag, ua rau nws yog virtual cross-linking. Lub cross-linking mob nyob ntawm qhov kub thiab txias. Thaum qhov kub nce, qhov cross-linking no maj mam qaug zog thiab ploj mus. Lub polymer muaj qee yam fluidity thiab tuaj yeem raug thermoplastic processing. Thaum qhov kub txo qis, qhov cross-linking no maj mam rov zoo thiab tsim dua. Kev ntxiv me me ntawm cov khoom sau ua rau qhov deb ntawm cov molecules nce, ua rau lub peev xwm los tsim cov hydrogen bonds ntawm cov molecules tsis muaj zog, thiab ua rau lub zog txo qis. Kev tshawb fawb tau qhia tias qhov kev txiav txim ntawm kev ruaj khov ntawm ntau pawg ua haujlwm hauv polyurethane roj hmab los ntawm siab mus rau qis yog: ester, ether, urea, carbamate, thiab biuret. Thaum lub sijhawm laus ntawm cov roj hmab polyurethane, thawj kauj ruam yog qhov tawg ntawm cov ntawv cog lus sib txuas ntawm biuret thiab urea, ua raws li kev tawg ntawm cov carbamate thiab urea bonds, uas yog, qhov tawg tseem ceeb.
01 Ua kom mos
Cov polyurethane elastomers, zoo li ntau yam khoom siv polymer, mos thaum kub siab thiab hloov pauv los ntawm lub xeev elastic mus rau lub xeev viscous, ua rau lub zog kho tshuab txo qis sai. Los ntawm kev xav txog tshuaj lom neeg, qhov kub ntawm elasticity feem ntau nyob ntawm cov yam xws li nws cov tshuaj lom neeg sib xyaw, qhov hnyav molecular, thiab qhov ceev ntawm crosslinking.
Feem ntau hais lus, kev nce qhov hnyav ntawm cov molecular, kev nce qhov rigidity ntawm cov ntu nyuaj (xws li kev qhia lub nplhaib benzene rau hauv cov molecule) thiab cov ntsiab lus ntawm cov ntu nyuaj, thiab kev nce qhov crosslinking density yog txhua yam zoo rau kev nce qhov kub softening. Rau thermoplastic elastomers, cov qauv molecular yog feem ntau linear, thiab qhov kub softening ntawm elastomer kuj nce ntxiv thaum qhov hnyav molecular nce ntxiv.
Rau cov polyurethane elastomers uas sib txuas ua ke, qhov ceev ntawm kev sib txuas ua ke muaj qhov cuam tshuam loj dua li qhov hnyav ntawm cov molecular. Yog li ntawd, thaum tsim cov elastomers, kev ua kom cov isocyanates lossis polyols ua haujlwm tau zoo dua tuaj yeem tsim cov qauv sib txuas ua ke ntawm cov tshuaj lom neeg uas ruaj khov hauv qee cov molecules elastic, lossis siv cov piv ntawm isocyanate ntau dhau los tsim cov qauv sib txuas ua ke ntawm isocyanate hauv lub cev elastic yog ib txoj hauv kev zoo los txhim kho qhov tiv taus cua sov, tiv taus cov kuab tshuaj, thiab lub zog kho tshuab ntawm elastomer.
Thaum PPDI (p-phenyldiisocyanate) siv ua cov khoom siv raw, vim yog kev sib txuas ncaj qha ntawm ob pawg isocyanate rau lub nplhaib benzene, qhov ntu nyuaj uas tsim muaj cov ntsiab lus ntawm lub nplhaib benzene siab dua, uas txhim kho qhov nruj ntawm qhov ntu nyuaj thiab yog li ua rau muaj kev tiv thaiv cua sov ntawm elastomer.
Los ntawm lub cev pom, qhov kub ntawm cov elastomers nyob ntawm qib ntawm kev sib cais microphase. Raws li cov ntawv tshaj tawm, qhov kub ntawm cov elastomers uas tsis dhau los ntawm kev sib cais microphase yog qis heev, nrog rau qhov kub ua tiav tsuas yog li 70 ℃, thaum cov elastomers uas dhau los ntawm kev sib cais microphase tuaj yeem ncav cuag 130-150 ℃. Yog li ntawd, kev nce qib ntawm kev sib cais microphase hauv elastomers yog ib qho ntawm cov txheej txheem zoo los txhim kho lawv cov cua sov tiv taus.
Qhov degree ntawm microphase sib cais ntawm elastomers tuaj yeem txhim kho los ntawm kev hloov pauv qhov sib piv ntawm qhov hnyav molecular ntawm cov saw hlau thiab cov ntsiab lus ntawm cov saw hlau tawv, yog li ua kom lawv cov cua sov tsis kam. Cov kws tshawb fawb feem ntau ntseeg tias qhov laj thawj rau microphase sib cais hauv polyurethane yog qhov thermodynamic tsis sib xws ntawm cov mos mos thiab cov tawv. Hom saw hlau extender, cov tawv thiab nws cov ntsiab lus, hom mos mos, thiab hydrogen bonding txhua yam muaj kev cuam tshuam loj rau nws.
Piv nrog cov diol saw extenders, diamine saw extenders xws li MOCA (3,3-dichloro-4,4-diaminodiphenylmethane) thiab DCB (3,3-dichloro-biphenylenediamine) tsim ntau pawg polar amino ester hauv elastomers, thiab ntau cov hydrogen bonds tuaj yeem tsim ntawm cov ntu nyuaj, ua rau muaj kev sib cuam tshuam ntawm cov ntu nyuaj thiab txhim kho qib ntawm microphase sib cais hauv elastomers; Symmetric aromatic saw extenders xws li p, p-dihydroquinone, thiab hydroquinone yog qhov zoo rau kev ua kom zoo thiab ntim cov ntu nyuaj, yog li txhim kho microphase sib cais ntawm cov khoom.
Cov amino ester segments uas tsim los ntawm aliphatic isocyanates muaj kev sib raug zoo nrog cov segments mos, ua rau cov segments tawv dua yaj hauv cov segments mos, txo qib ntawm kev sib cais microphase. Cov amino ester segments uas tsim los ntawm aromatic isocyanates muaj kev sib raug zoo tsis zoo nrog cov segments mos, thaum qib ntawm kev sib cais microphase siab dua. Polyolefin polyurethane muaj cov qauv sib cais microphase yuav luag tiav vim tias cov segments mos tsis tsim cov hydrogen bonds thiab cov hydrogen bonds tsuas yog tshwm sim hauv cov segments tawv.
Qhov cuam tshuam ntawm hydrogen bonding rau ntawm qhov softening ntawm elastomers kuj tseem ceeb. Txawm hais tias polyethers thiab carbonyls hauv qhov mos mos tuaj yeem tsim ntau cov hydrogen bonds nrog NH4 hauv qhov nyuaj, nws kuj ua rau qhov kub ntawm elastomers softening nce ntxiv. Nws tau lees paub tias hydrogen bonds tseem khaws cia 40% ntawm 200 ℃.
02 Kev rhuav tshem cua sov
Cov pawg amino ester raug rhuav tshem hauv qab no ntawm qhov kub siab:
- RNHCOOR – RNC0 HO-R
- RNHCOOR – RNH2 CO2 ene
- RNHCOOR – RNHR CO2 ene
Muaj peb hom tseem ceeb ntawm kev rhuav tshem cov khoom siv polyurethane los ntawm thermal:
① Tsim cov isocyanates thiab polyols thawj;
② α— Cov pa oxygen ntawm CH2 lub hauv paus tawg thiab sib xyaw nrog ib qho hydrogen bond ntawm CH2 thib ob los tsim cov amino acids thiab alkenes. Cov amino acids decompose rau hauv ib qho amine thawj thiab carbon dioxide:
③ Daim ntawv 1 theem nrab amine thiab carbon dioxide.
Kev rhuav tshem cov qauv carbamate los ntawm cua sov:
Aryl NHCO Aryl, ~ 120 ℃;
N-alkyl-NHCO-aryl, ~ 180 ℃;
Aryl NHCO3 n-alkyl, ~ 200 ℃;
N-alkyl-NHCO-n-alkyl, ~ 250 ℃.
Qhov kev ruaj khov ntawm cov amino acid esters muaj feem cuam tshuam nrog cov hom khoom pib xws li isocyanates thiab polyols. Aliphatic isocyanates siab dua li aromatic isocyanates, thaum cov cawv rog siab dua li cov cawv aromatic. Txawm li cas los xij, cov ntaub ntawv qhia tias qhov kub ntawm kev rhuav tshem thermal ntawm aliphatic amino acid esters yog nruab nrab ntawm 160-180 ℃, thiab ntawm aromatic amino acid esters yog nruab nrab ntawm 180-200 ℃, uas tsis sib xws nrog cov ntaub ntawv saum toj no. Qhov laj thawj yuav muaj feem cuam tshuam nrog txoj kev sim.
Qhov tseeb, aliphatic CHDI (1,4-cyclohexane diisocyanate) thiab HDI (hexamethylene diisocyanate) muaj kev tiv taus cua sov zoo dua li cov tshuaj tsw qab MDI thiab TDI feem ntau. Tshwj xeeb tshaj yog trans CHDI nrog cov qauv symmetrical tau raug lees paub tias yog isocyanate tiv taus cua sov tshaj plaws. Polyurethane elastomers npaj los ntawm nws muaj cov txheej txheem ua tau zoo, kev tiv taus hydrolysis zoo heev, qhov kub thiab txias softening siab, qhov kub hloov iav qis, thermal hysteresis qis, thiab UV siab.
Ntxiv rau pawg amino ester, polyurethane elastomers kuj muaj lwm pawg ua haujlwm xws li urea formate, biuret, urea, thiab lwm yam. Cov pawg no tuaj yeem dhau los ua thermal decomposition ntawm qhov kub siab:
NHCONCOO – (aliphatic urea formate), 85-105 ℃;
- NHCONCOO – (aromatic urea formate), ntawm qhov kub thiab txias ntawm 1-120 ℃;
- NHCONCONH – (aliphatic biuret), ntawm qhov kub thiab txias txij li 10 ° C txog 110 ° C;
NHCONCONH – (aroma biuret), 115-125 ℃;
NHCONH – (aliphatic urea), 140-180 ℃;
- NHCONH – (aromatic urea), 160-200 ℃;
Isocyanurate nplhaib> 270 ℃.
Qhov kub ntawm kev rhuav tshem ntawm biuret thiab urea raws li formate qis dua li ntawm aminoformate thiab urea, thaum isocyanurate muaj qhov kub zoo tshaj plaws. Hauv kev tsim cov elastomers, cov isocyanates ntau dhau tuaj yeem cuam tshuam nrog cov aminoformate thiab urea uas tsim los ua urea raws li formate thiab biuret cross-linked structures. Txawm hais tias lawv tuaj yeem txhim kho cov khoom siv kho tshuab ntawm elastomers, lawv tsis ruaj khov rau cua sov.
Yuav kom txo tau cov pawg tsis ruaj khov thermal xws li biuret thiab urea formate hauv elastomers, nws yog ib qho tsim nyog los xav txog lawv cov khoom siv raw thiab cov txheej txheem ntau lawm. Yuav tsum siv cov isocyanate ratios ntau dhau, thiab lwm txoj kev yuav tsum siv ntau li ntau tau los ua ntej tsim cov nplhaib isocyanate ib nrab hauv cov khoom siv raw (feem ntau yog isocyanates, polyols, thiab cov saw hlau txuas ntxiv), thiab tom qab ntawd qhia lawv rau hauv elastomer raws li cov txheej txheem ib txwm muaj. Qhov no tau dhau los ua txoj hauv kev siv ntau tshaj plaws rau kev tsim cov polyurethane elastomers uas tiv taus cua sov thiab nplaim taws.
03 Hydrolysis thiab thermal oxidation
Cov polyurethane elastomers feem ntau yuav raug cua sov rhuav tshem hauv lawv cov ntu tawv thiab cov kev hloov pauv tshuaj sib xws hauv lawv cov ntu mos ntawm qhov kub siab. Polyester elastomers tsis muaj dej tsis kam thiab muaj qhov hnyav dua rau hydrolyze ntawm qhov kub siab. Lub neej ua haujlwm ntawm polyester / TDI / diamine tuaj yeem ncav cuag 4-5 lub hlis ntawm 50 ℃, tsuas yog ob lub lis piam ntawm 70 ℃, thiab tsuas yog ob peb hnub saum toj no 100 ℃. Ester bonds tuaj yeem rhuav tshem mus rau hauv cov kua qaub thiab cawv sib xws thaum raug dej kub thiab pa, thiab urea thiab amino ester pawg hauv elastomers kuj tuaj yeem dhau los ntawm hydrolysis reactions:
RCOOR H20- → RCOOH HOR
Cawv ester
Ib RNHCONHR ib H20- → RXHCOOH H2NR -
Ureamide
Ib RNHCOOR-H20- → RNCOOH HOR -
Amino formate ester Amino formate cawv
Cov polyether elastomers muaj kev ruaj khov thermal oxidation tsis zoo, thiab ether elastomers α- Cov hydrogen ntawm cov pa roj carbon atom yooj yim oxidized, tsim cov hydrogen peroxide. Tom qab ntxiv decomposition thiab cleavage, nws tsim cov oxide radicals thiab hydroxyl radicals, uas thaum kawg decompose rau hauv formates lossis aldehydes.
Cov polyesters sib txawv muaj qhov cuam tshuam me ntsis rau qhov tsis kam ntawm cov elastomers, thaum cov polyethers sib txawv muaj qee yam cuam tshuam. Piv nrog TDI-MOCA-PTMEG, TDI-MOCA-PTMEG muaj lub zog tensile khaws cia ntawm 44% thiab 60% feem thaum laus ntawm 121 ℃ rau 7 hnub, nrog rau qhov tom kawg zoo dua li qhov qub. Qhov laj thawj yuav yog tias PPG molecules muaj cov saw hlau, uas tsis zoo rau kev npaj tsis tu ncua ntawm cov molecules elastic thiab txo qhov tsis kam ntawm lub cev elastic. Qhov kev txiav txim siab thermal stability ntawm polyethers yog: PTMEG> PEG> PPG.
Lwm cov pab pawg ua haujlwm hauv polyurethane elastomers, xws li urea thiab carbamate, kuj dhau los ntawm kev ua oxidation thiab hydrolysis reactions. Txawm li cas los xij, pawg ether yog qhov yooj yim oxidized tshaj plaws, thaum pawg ester yog qhov yooj yim hydrolyzed tshaj plaws. Qhov kev txiav txim ntawm lawv cov antioxidant thiab hydrolysis tsis kam yog:
Kev ua haujlwm tiv thaiv kab mob: esters> urea> carbamate> ether;
Kev tsis kam rau hydrolysis: ester
Txhawm rau txhim kho qhov tsis kam oxidation ntawm polyether polyurethane thiab qhov tsis kam hydrolysis ntawm polyester polyurethane, cov khoom ntxiv kuj tau ntxiv, xws li ntxiv 1% phenolic antioxidant Irganox1010 rau PTMEG polyether elastomer. Lub zog tensile ntawm elastomer no tuaj yeem nce ntxiv 3-5 zaug piv rau tsis muaj antioxidants (cov txiaj ntsig xeem tom qab laus ntawm 1500C rau 168 teev). Tab sis tsis yog txhua yam antioxidant muaj cov nyhuv rau polyurethane elastomers, tsuas yog phenolic 1rganox 1010 thiab TopanOl051 (phenolic antioxidant, hindered amine light stabilizer, benzotriazole complex) muaj cov teebmeem tseem ceeb, thiab tus qub yog qhov zoo tshaj plaws, tej zaum vim phenolic antioxidants muaj kev sib raug zoo nrog elastomers. Txawm li cas los xij, vim yog lub luag haujlwm tseem ceeb ntawm cov pab pawg phenolic hydroxyl hauv cov txheej txheem ruaj khov ntawm phenolic antioxidants, txhawm rau kom tsis txhob muaj kev cuam tshuam thiab "kev ua tsis tiav" ntawm cov pab pawg phenolic hydroxyl no nrog cov pab pawg isocyanate hauv lub kaw lus, qhov piv ntawm isocyanates rau polyols yuav tsum tsis txhob loj dhau, thiab cov tshuaj antioxidants yuav tsum tau ntxiv rau prepolymers thiab cov saw hlau txuas ntxiv. Yog tias ntxiv thaum lub sijhawm tsim cov prepolymers, nws yuav cuam tshuam loj heev rau qhov cuam tshuam ruaj khov.
Cov tshuaj ntxiv uas siv los tiv thaiv hydrolysis ntawm polyester polyurethane elastomers feem ntau yog carbodiimide compounds, uas cuam tshuam nrog carboxylic acids tsim los ntawm ester hydrolysis hauv polyurethane elastomer molecules los tsim cov acyl urea derivatives, tiv thaiv kev hydrolysis ntxiv. Kev ntxiv carbodiimide ntawm qhov feem pua ntawm 2% txog 5% tuaj yeem ua rau cov dej ruaj khov ntawm polyurethane ntau dua 2-4 zaug. Tsis tas li ntawd, tert butyl catechol, hexamethylenetetramine, azodicarbonamide, thiab lwm yam kuj muaj qee yam kev cuam tshuam tiv thaiv hydrolysis.
04 Cov yam ntxwv tseem ceeb ntawm kev ua tau zoo
Polyurethane elastomers yog cov copolymers ntau thaiv, nrog rau cov saw hlau molecular tsim los ntawm cov ntu hloov pauv tau nrog qhov kub hloov pauv iav qis dua qhov kub hauv chav thiab cov ntu tawv nrog qhov kub hloov pauv iav siab dua qhov kub hauv chav. Ntawm lawv, oligomeric polyols tsim cov ntu hloov pauv tau, thaum diisocyanates thiab cov saw hlau me me tsim cov ntu tawv. Cov qauv embedded ntawm cov ntu hloov pauv tau thiab tawv txiav txim siab lawv cov kev ua tau zoo tshwj xeeb:
(1) Qhov nyuaj ntawm cov roj hmab ib txwm feem ntau yog nyob nruab nrab ntawm Shaoer A20-A90, thaum qhov nyuaj ntawm cov yas yog li Shaoer A95 Shaoer D100. Polyurethane elastomers tuaj yeem ncav cuag qis li Shaoer A10 thiab siab li Shaoer D85, tsis tas yuav tsum tau kev pab ntxiv;
(2) Lub zog siab thiab elasticity tseem tuaj yeem tswj tau hauv ntau yam kev nyuaj;
(3) Kev tiv thaiv zoo heev, 2-10 npaug ntawm cov roj hmab ntuj;
(4) Kev tiv taus zoo heev rau dej, roj, thiab tshuaj lom neeg;
(5) Kev tiv taus kev cuam tshuam siab, kev tiv taus qaug zog, thiab kev tiv taus kev co, tsim nyog rau kev siv khoov zaus siab;
(6) Kev tiv thaiv kub qis zoo, nrog rau qhov kub qis qis dua -30 ℃ lossis -70 ℃;
(7) Nws muaj kev ua tau zoo heev ntawm kev rwb thaiv tsev, thiab vim nws cov thermal conductivity qis, nws muaj cov nyhuv rwb thaiv tsev zoo dua piv rau roj hmab thiab yas;
(8) Cov khoom siv biocompatibility zoo thiab cov tshuaj anticoagulant;
(9) Kev rwb thaiv hluav taws xob zoo heev, tiv taus pwm, thiab UV ruaj khov.
Cov polyurethane elastomers tuaj yeem tsim tau siv cov txheej txheem zoo ib yam li cov roj hmab ib txwm muaj, xws li kev ua kom yas, kev sib tov, thiab kev sib xyaw ua ke. Lawv kuj tuaj yeem ua pwm ua cov roj hmab ua kua los ntawm kev nchuav, kev txhaj tshuaj centrifugal, lossis kev txau. Lawv kuj tuaj yeem ua rau cov khoom siv granular thiab tsim los ntawm kev txhaj tshuaj, extrusion, dov, tshuab molding, thiab lwm yam txheej txheem. Ua li no, nws tsis yog tsuas yog txhim kho kev ua haujlwm zoo xwb, tab sis nws kuj txhim kho qhov tseeb ntawm qhov ntev thiab qhov tsos ntawm cov khoom.
Lub sijhawm tshaj tawm: Lub Kaum Ob Hlis-05-2023