Kev Sib Tw Deposition hauv Nanocellulose Processing
Nanocellulose suspensions (2 wt%, viscosity 10,000 cP ntawm 70 degree) yog siv rau biodegradable film casting. Nyob rau hauv laminar ntws (Re 200), cellulose nanofibrils tso rau ntawm qhov chaw rhuab, tsim insulating kub qhov chaw. The PFA heater's surface charge density (zeta potential) determines electrostatic interactions with negatively charged cellulose fibrils. Kev soj ntsuam ntau los ntawm 8 zaj duab xis casting kab qhia tau hais tias PFA nrog zeta muaj peev xwm qis dua -30 mV txo cov fibril deposition los ntawm 85% piv rau cov chaw ze ntawm isoelectric point (0 mV), ncua kev tu ncua ntawm 3 hnub mus rau 21 hnub.
Zeta Potential thiab Fibril Adhesion Mechanism
Cellulose nanofibrils (3-5 nm dav, 100-1000 nm ntev) muaj qhov tsis zoo zeta muaj peev xwm (-25 txog -40 mV ntawm pH 7) vim yog pawg carboxylate. PFA nto nqi pib los ntawm oxidation thaum ua. PFA qhov chaw tsis zoo tiv thaiv cov fibrils, txo cov deposition. Qhov zoo lossis nruab nrab qhov chaw nyiam cov fibrils. Kev ntsuas ntawm 70 degree, pH 7, 0.1 m / s ntws (Re 200):
| PFA Surface Treatment | Zeta Potential ntawm pH 7 (mV) | Fibril Deposition Rate (mg / cm²) teev | Lub sij hawm mus rau 0.5mm Deposit (teev) | Thaum tshav kub kub hloov pauv ntawm 500h |
|---|---|---|---|---|
| Raws li - molded (oxidized) | -15 | 1.2 | 35 | 40% |
| Kev kho ntshav ntshav (O₂) | -35 | 0.4 | 100 | 15% |
| Plasma kev kho mob (siab zog) | -45 | 0.2 | 200 | 8% |
| Kev kho mob Corona | -30 | 0.5 | 85 | 18% |
| Tshuaj passivation | -5 | 2.5 | 15 | 60% |
Flow Regime thiab Deposition Kinetics
Laminar flow (Re 200) tsim cov phab ntsa qis shear stress (1-2 Pa), tsis txaus tshem tawm cov fibrils deposited. Kev tso nyiaj feem ntau yog tswj los ntawm electrostatic thiab van der Waals rog. Ntawm Re> 1000 (turbulent), shear stress tshaj 10 Pa, tshem tawm cov fibers uas tsis muaj zog tsis hais txog qhov muaj peev xwm zeta.
| Flow Velocity | Re | Phab ntsa Shear (Pa) | Dominant Deposition Mechanism | Zeta Muaj Peev Xwm Tseem Ceeb |
|---|---|---|---|---|
| 0.05 m/s | 100 | 0.8 | Electrostatic | Tseem ceeb |
| 0.10 m/s | 200 | 1.5 | Electrostatic + diffusion | Siab |
| 0.20 m/s | 400 | 3.0 | Mixed | Nruab nrab |
| 0.50 m/s | 1000 | 8.0 | Shear{0}} tswj | Tsawg |
Surface Charge Stability ntawm 70 degree
Plasma- kho PFA qhov chaw degrade hauv dej kub, poob tsis zoo thaum lub sijhawm. Zeta muaj peev xwm ntawm plasma- kho PFA (thawj -35 mV) txo mus rau -25 mV tom qab 500 teev, -18 mV tom qab 1000 teev ntawm 70℃hauv dej. Rau kev pabcuam nanocellulose ntev, qhia txog kev kho mob corona uas tsim cov txheej txheem sib sib zog nqus (10-20 nm vs . 2-5 nm rau ntshav), tswj -30 mV rau 2000+ teev.
Phab ntsa Thickness thiab Deposit Thermal Resistance
Thaum fibrils tso nyiaj, cov phab ntsa tuab PFA muab cov thermal buffering tab sis tsis tiv thaiv kev tso nyiaj. Rau tus qauv PFA (zeta -15 mV) nrog 0.5 hli tso nyiaj tom qab 35 teev:
| Phab ntsa Thickness | Deposit Thickness ntawm 500h | Tag Nrho Thermal Resistance (PFA + deposit) | Nto kub nce | Yuav tsum tau ntxuav (teev) |
|---|---|---|---|---|
| 1.5 hli | 4.2mm ib | 0.025 m²·K/W | +35 degree | 40 |
| 2.0 hli | 4.2mm ib | 0.028 | +39 degree | 40 |
| 2.5 hli | 4.2mm ib | 0.031 | +43 degree | 40 |
Rau siab -zeta PFA (-35 mV) nrog qhov tso nyiaj tsawg kawg nkaus (0.2 hli ntawm 500h), kev tu ncua ncua mus rau 200+ teev tsis hais txog ntawm phab ntsa tuab.
pH thiab Suspension Chemistry Effects
Nanocellulose zeta muaj peev xwm ua tsis zoo ntawm pH siab dua. Ntawm pH 8, fibrils ncav cuag -45 mV, nce repulsion los ntawm nruab nrab nqi PFA. Ntawm pH 6 (muaj peev xwm los ntawm residual acid), fibrils poob mus rau -15 mV, nce deposition. Rau kev ua haujlwm ruaj khov, tswj pH 7-8. Ntxiv ntawm carboxymethyl cellulose (0.1%) nce kev ncua viscosity tab sis kuj nce nqi tsis zoo, txo cov deposition los ntawm 50% ntawm tus qauv PFA.
Specification Guide rau Nanocellulose Heaters
Rau 2% nanocellulose suspension ntawm 70 degree, pH 7, qhia PFA cov cua sov nrog corona kev kho mob ua tiav zeta muaj peev xwm hauv qab no -30 mV ( ntsuas los ntawm electrokinetic analyzer ntawm 70℃). Yuav tsum tau muab ntawv pov thawj ntawm zeta muaj peev xwm tom qab 1000- teev rau hauv dej 70 degree. Rau cov phab ntsa thickness, 2.0mm yog txaus thaum deposition yog tswj. Rau laminar flow systems (Re <500), qhia zeta muaj peev xwm hauv qab -35 mV. Tus nqi them rau corona-kho PFA (15-25% dhau tus qauv) yog tsim nyog los ntawm kev ncua kev tu ncua los ntawm 3 hnub mus rau 3 lub lis piam hauv kev nruam nanocellulose zaj duab xis casting, qhov twg downtime rau kev tshem tawm cov nqi $ 5,000-20,000 ib qhov xwm txheej. Rau R&D systems, plasma-kho PFA nrog kev tu txhua lub lim tiam tuaj yeem ua tau. Rau turbulent flow (Re> 1000), tus qauv PFA nrog 2.5mm phab ntsa yog txaus.
