Tsawg-Density polyethylene (LDPE), raws li qeb tseem ceeb ntawm kev dav dav- lub hom phiaj thermoplastic resins, tshuav nws qhov kev ua tau zoo rau nws cov tshuaj lom neeg muaj pes tsawg leeg thiab cov qauv molecular.Thaum qib molecular, LDPE yog tsim los ntawm ethylene monomers los ntawm cov dawb radical polymerization. Nws cov ntsiab lus tseem ceeb yog carbon (C) thiab hydrogen (H), nrog rau cov tshuaj formula (C₂H₄)ₙ, qhov twg n sawv cev rau qib ntawm polymerization, feem ntau yog li ntawm ntau txhiab mus txog kaum txhiab.
Cov qauv molecular ntawm LDPE yog nyob ntawm qhov ntev -chain alkanes, tab sis nws qhov sib txawv tseem ceeb los ntawm siab -density polyethylene (HDPE) nyob rau hauv siab - ntom ntom faib ntawm nws cov ceg ntoo. Thaum lub sij hawm polymerization, cov saw dawb radical cuam tshuam yooj yim ua rau cov saw hlau hloov mus, ua rau muaj ntau cov ceg luv luv (xws li methyl thiab ethyl) thiab cov ceg ntev me me ntawm cov saw tseem ceeb. Cov ceg ntoo no cuam tshuam qhov kev sib koom ua ke ntawm cov saw hlau molecular, cuam tshuam kev tsim cov cheeb tsam crystalline thiab ua rau cov crystallinity tsuas yog 40% -60% (txog qis dua HDPE's 80% -90%). Qhov no yog qhov ncaj qha ua rau nws tus yam ntxwv "tsawg ceev" - nws qhov ntom ntom yog feem ntau 0.910-0.940 g / cm³.
Los ntawm cov ntsiab lus muaj pes tsawg leeg, LDPE muaj kwv yees li 85.7% carbon thiab 14.3% hydrogen, uas yuav luag tsis muaj lwm yam impurities (kev lag luam- cov khoom lag luam qib yuav muaj cov lej ntawm cov catalyst residue lossis antioxidants, tab sis cov qauv tseem ceeb tseem yog cov ntshiab hydrocarbon). Qhov no yooj yim tshuaj muaj pes tsawg leeg endows nws nrog zoo heev tshuaj inertness: nws yog insoluble nyob rau hauv acids, alkalis, thiab feem ntau organic solvents nyob rau hauv chav tsev kub, tsuas yog maj mam o nyob rau hauv siab - boiling - taw tes hydrocarbons (xws li toluene); ib txhij, nws cov pa roj carbon saturated-hydrogen bond qauv muab nws cov huab cua tsis zoo thiab hluav taws xob rwb thaiv tsev, ua rau nws tsim nyog rau ntim sab nraum zoov thiab tiv thaiv hluav taws xob tiv thaiv.
Nws yog ib qho tseem ceeb uas yuav tsum tau hais txog tias LDPE muaj qhov dav molecular hnyav tis (polydispersity Performance index ntawm kwv yees li 2-6), tus yam ntxwv ze ze rau nws cov txheej txheem polymerization. Qhov dav molecular hnyav tis ua kom zoo yaj flowability (paub kev ua thiab molding) thiab txhim khu cov khoom toughness los ntawm cov synergistic nyhuv ntawm txawv molecular hnyav saw ntu-cov saw luv muab kev txhawb nqa nruj, thaum ntev chains nqus lub zog los ntawm entanglement.
Zuag qhia tag nrho, cov tshuaj lom neeg muaj pes tsawg leeg ntawm LDPE yog nyob rau ntawm ethylene monomers, ua tiav qhov sib npaug ntawm qhov ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ntom ethylene monomer Nws cov pob txha hydrocarbon yooj yooj yim thiab cov ceg tshwj xeeb faib ua ke tsim nws txoj haujlwm tsis tuaj yeem hloov pauv hauv cov yeeb yaj kiab, txhaj tshuaj molding, thiab lwm yam. Nrog rau kev xav tau ntau ntxiv rau kev tsim ntsuab, kev tswj xyuas meej ntawm nws cov tshuaj muaj pes tsawg leeg (xws li txo cov ceg ntom ntom kom rov ua dua tshiab) tau dhau los ua cov kev taw qhia tshiab rau kev tshawb fawb kev lag luam.