Compositi a matrice termoplastica perch
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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:

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Compositi a matrice termoplastica: perché?

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Compositi a matrice termoplastica perch

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


Matrici tp rinforzo

HDPE

PP

ABS

PA12

PPE

PEEK PPS

Fibre di vetro

Fibre di carbonio

aramidi, poliammidi

poliesteri

polietilene

polipropilene

Matrici TP Rinforzo

compositi


Poli fenilen etere ppe

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


Polichetoni

Polichetoni

Cristallini (30%), trasparenti buone proprietà meccaniche

Tg 143°C, Tm 334°C per parti soggette ad alte temperature (240-280°C) e in mezzi aggressivi nei trasporti, reattori chimici in elettronica

compositi


Poli fenilen solfuro pps

Poli(fenilen solfuro) PPS

Altamente cristallino (60%), Tg 85°C, Tm 285°C per usi in continuo a 200-240°C, resistenti alla fiamma, resistenti a acidi e basi ma meno agli agenti ossidanti. Per apparecchiature in cucina, nel settore automotive ed industriale

compositi


Applicazioni

  • Componentistica per biciclette da corsa

  • Giubbotti di salvataggio

  • Elmetti

  • Schienali di zaini

  • Componenti di ali di aerei

Applicazioni

Applicati specialmente per materiali “leggeri” ad alte prestazioni

Hanno buona resilienza (resistenza all’impatto) e inerzia chimica :

compositi


Compositi a matrice termoplastica perch

producer:

producer:

producer:

producer:

Fokker Special Products

Campagnolo

Cato Composites

Halmatic

material:

material:

material:

material:

Twintex glass/PP

TEPEX aramid/PA6

glass/PPS

Tepex carbon/PA6.6

production volume:

production volume:

production volume:

production volume:

> 100.000/year

< 100/year

50.000/year

~ 500/year

production process:

production process:

production process:

production process:

vacuum moulding

vacuum moulding

high spead pressing

high speed pressing

application reasons:  

application reasons:  

application reasons:  

application reasons:  

superior performance, automation, cost

stiffness/weight, reduction parts number, cost

weight, quality, cycle times, automation, costs

cost, impact resistance, emission harmful gasses

  • racing bicycle components

  • lifeboat

  • antiballistic helm

  • wing leading edge

compositi


Lavorazione dei compositi termoplastici

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’elevataviscosità del fuso termoplastico (tra 10-100 Pa.s. in confronto a 0.2-2Pa.s. dei sistemi termoindurenti).

compositi


Compositi a matrice termoplastica perch

compositi


Lavorazione dei compositi termoplastici1

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


Compositi a matrice termoplastica perch

Prepregs:

(fogli preimpregnati)

Via secca

Via umida

compositi


Compositi a matrice termoplastica perch

Filamento di Rinforzo

Filamento di Polimero

sezione

Sandwich di un tessuto di rinforzo tra due film di termoplastico

Commingled fibres

(commistione di fibre)

Commistione realizzata in situ per ottenere un distribuzione omogenea delle due popolazioni di fibre

compositi


Compositi a matrice termoplastica perch

Fibre preimpregnate

Powder impregnated tows

(con polveri)

Fibre Impregnated Thermoplastic, FIT

(in guaina)

compositi


Compositi a matrice termoplastica perch

Short and long fibres reinforced polymer pellets

Fibra corta

<1mm

Pellets rinforzati

Fibra lunga

<1cm

compositi


Lavorazione dei compositi termoplastici2

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


Stampaggio

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


Commistione di fibre

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


Laminazione prepregs

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


Compositi a matrice termoplastica perch

Filament winding

Pultrusion

Thermoforming

Compression Moulding

compositi


Potenzialit dei compositi termoplastici

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


Reinforcement of profiles

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


Compositi a matrice termoplastica perch

compositi


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