Compositi a matrice termoplastica: perché?

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1 Compositi a matrice termoplastica: perché?
Le resine termoindurenti sono fragili non possono essere rifuse o ri- formate. I termoplastici sono tenaci e possono erre ri-fusi e ri-formati, (polietilene, nylon, polipropilene..). Altri vantaggi dei compositi a matrice termoplastica: La frazione in volume di fibre può essere variata nello spessore (da 0 to ~65%-) Robustezza, dovuta alla tenacità dei sistemi termoplastici Impatto ambientale in genere minore dovuto alla possibilità di ri-formare i pezzi, riciclarli e saldarli Minor costo delle materie prime e prolungata “shell life” Potenzialmente adatti per processi di lavorazione più veloci compositi

2 Matrici TP Rinforzo Fibre di vetro Fibre di carbonio
aramidi, poliammidi poliesteri polietilene polipropilene HDPE PP ABS PA12 PPE PEEK PPS compositi

3 Poli(fenilen etere) PPE
PPE, è un engineering thermoplastics, molto resistente alle alte temperature. (Tg 210 oC) Per questo molto spesso è usato in miscela (blends) con HIPS. La miscelazione rende il sistema più facile alla lavorazione e con buona resilienza. (PPE da solo è molto fragile) General Electric vende PPO/HIPS blends con il nome di NorylTM. compositi

4 Polichetoni Cristallini (30%), trasparenti buone proprietà meccaniche
Tg 143°C, Tm 334°C per parti soggette ad alte temperature ( °C) e in mezzi aggressivi nei trasporti, reattori chimici in elettronica compositi

5 Poli(fenilen solfuro) PPS
Altamente cristallino (60%), Tg 85°C, Tm 285°C per usi in continuo a °C, resistenti alla fiamma, resistenti a acidi e basi ma meno agli agenti ossidanti. Per apparecchiature in cucina, nel settore automotive ed industriale compositi

6 Applicazioni Applicati specialmente per materiali “leggeri” ad alte prestazioni Hanno buona resilienza (resistenza all’impatto) e inerzia chimica :                                                                                                                                                                  Componentistica per biciclette da corsa Giubbotti di salvataggio Elmetti Schienali di zaini Componenti di ali di aerei compositi

7 racing bicycle components
producer: Campagnolo material: Tepex carbon/PA6.6 production volume: > /year production process: high spead pressing application reasons:   weight, quality, cycle times, automation, costs racing bicycle components lifeboat antiballistic helm wing leading edge producer: Halmatic material: Twintex glass/PP production volume: ~ 500/year production process: vacuum moulding application reasons:   cost, impact resistance, emission harmful gasses producer: Cato Composites material: TEPEX aramid/PA6 production volume: 50.000/year production process: high speed pressing application reasons:   superior performance, automation, cost producer: Fokker Special Products material: glass/PPS production volume: < 100/year production process: vacuum moulding application reasons:   stiffness/weight, reduction parts number, cost compositi

8 LAVORAZIONE DEI COMPOSITI TERMOPLASTICI
Per formare i compositi a matrice termoplastica i polimeri devono essere : fusi o rammolliti mescolati intimamente con le fibre messi in forma, Non avvengono reazioni chimiche a differenza di quanto accade con i materiali termoindurenti. Svantaggi: maggior difficoltà di impregnazione delle fibre in confronto ai materiali compositi a matrice termoindurente a causa dell’elevata viscosità del fuso termoplastico (tra Pa.s. in confronto a Pa.s. dei sistemi termoindurenti). compositi

9 compositi

10 LAVORAZIONE DEI COMPOSITI TERMOPLASTICI
Processi a 2 stadi Primo stadio: formazione del “precursore” : Commingled fibres: tows of continuous fibres of glass or carbon intermingled with continuous fibres of the polymer Prepregs: Reinforcement fibres impregnated with a polymer matrix in the form of thin sheets Powder impregnated tows: Continuous tows of fibres are impregnated with thermoplastic powder giving a flexible ribbon or sheet Fibre Impregnated Thermoplastic, FIT: Powder impregnated continuous fibres encased in a polymer sheath Short and long fibre reinforced polymer pellets: compounded for subsequent extrusion or injection moulding compositi

11 Prepregs: (fogli preimpregnati) Via secca Via umida compositi

12 Sandwich di un tessuto di rinforzo tra due film di termoplastico
sezione Commingled fibres (commistione di fibre) Commistione realizzata in situ per ottenere un distribuzione omogenea delle due popolazioni di fibre Filamento di Rinforzo Filamento di Polimero compositi

13 Fibre preimpregnate Powder impregnated tows (con polveri)
Fibre Impregnated Thermoplastic, FIT (in guaina) compositi

14 Fibra corta <1mm Pellets rinforzati Fibra lunga <1cm
Short and long fibres reinforced polymer pellets Fibra corta <1mm Pellets rinforzati Fibra lunga <1cm compositi

15 LAVORAZIONE DEI COMPOSITI TERMOPLASTICI
Processi a 2 stadi. Secondo stadio formazione del precursore nel manufatto finale. Si possono usare diverse tecnologie di messa in forma Stampaggio Commistione di fibre Laminazione (prepregs) compositi

16 Stampaggio Large scale production of reinforced thermoplastics has so far centred on the injection moulding or extrusion of long and short fibre reinforced pellets. Here the fibres are incorporated to improve mechanical performance of the resultant moulding. short fibre - fibres of up to 3mm in length long fibre - fibres up to 13mm in length During processing most fibres are damaged The orientation of the fibres is determined by the shear profile within the die or mould. The reinforcing effect is greatest in the direction of the fibre. compositi

17 Commistione di Fibre: Commingled fibres are fibres of the polymer and reinforcement fibre intermingled together. As with all precursors they are only available in a fixed volume fractions, and limited range of colours, polymer types, additives etc. pultrusion is the most common processing for commingled fibres compositi

18 Laminazione (Prepregs):
Prepregs are sheets or tapes of reinforcement fibres pre- impregnated with a thermoplastic resin. They can then be laid and stacked up to form a composite structure. Unlike thermoset prepreg they are not tacky and require very different treatment to their thermoset matrix counterparts. Thermoforming is a suitable technology for prepregs compositi

19 Filament winding Pultrusion Thermoforming Compression Moulding
compositi

20 Potenzialità dei compositi termoplastici
The broader use of advanced composites is currently inhibited by high material and manufacturing costs. Thermoplastics are generally low cost. The processing steps for the manufacture of thermoplastic composites are much simpler than for thermoset as no chemical reactions are involved. However, existing thermoplastic composite manufacturing routes are all two stage processes. The full potential of thermoplastic composites will not be achieved until a one stage manufacturing method has been developed. one stage manufacturing process for the production of thermoplastic composite profiles with the aesthetics of an extrusion and the mechanical performance of a fibreglass pultrusion one stage process for the manufacture of selectively reinforced extruded profiles Manufacturing process for the production of prepreg tapes with high fibre alignment compositi

21 Reinforcement of profiles
This technology allows the use of variable fibre reinforcement levels of 0% to about 65% by volume across the profile. By careful design of the profile it is possible to restrict the area of the reinforcement to the region where it provides most mechanical benefit, with the rest of the profile being formed with the cheaper polymer. The overall stiffness is very similar to conventional composites even though the reinforcement level is greatly reduced. This is especially useful when expensive carbon fibres are employed.. Even though carbon fibres are more expensive than glass fibres this need not be reflected in the profile cost. It could also provide a further advantage in terms of reduced weight. compositi

22 compositi