compositi

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

compositi

R

R

OHO2, Cu cat

O

R

R

R

R

O H

n

n + n H2O

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

HO OH F C

O

Fn nK2CO3

O C

O

O 2n KF

n

PEEK

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

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

Applicati specialmente per materiali “leggeri” ad alte prestazioniHanno buona resilienza (resistenza all’impatto) e inerzia chimica :

compositi

producer: Campagnolo

material: Tepex carbon/PA6.6

production volume:

> 100.000/year

production process:

high spead pressing

application reasons:  

weight, quality, cycle times, automation, costs

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

•racing bicycle components

•lifeboat

•antiballistic helm

•wing leading edge

compositi

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 10-100 Pa.s. in confronto a 0.2-2Pa.s. dei sistemi termoindurenti).

compositi

C o m m is tio ned i

F ib re

fo g lip re im p reg n a ti

Tessutote rm ofo rm a tu ra

s ta m p ag g io

filatof ila m en t w ind in g ,

p u ltu sio ne

S ta m p a gg io (a p re ss io n e)T e rm o fo rm a tu ra

Con polveri:P o ltrus io ne

In guaina:f ila m en t w in d ing

Fibra corta:S ta m p ag g io a in ie zio ne

Fibra lunga:s ta m p a gg io a d in ie zio ne

s tep 2

in gu a ina

co n po lve ri

f ib rep re im pre gn a te

fib ra lun g a (1 cm )

fib ra co rta (1 m m )

p e lle tsrin fo rza ti

S tep 1

C O M P O S IT I A M A T R IC IE T E R M O P L A S T IC AP ro cess ing

compositi

LAVORAZIONE DEI COMPOSITI TERMOPLASTICI

Processi a 2 stadiProcessi 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

Prepregs:(fogli preimpregnati)

Via secca

Via umida

compositi

Sandwich di un tessuto di rinforzo tra due film di termoplastico

Commingled fibres (commistione di fibre)

sezione

Filamento di RinforzoFilamento di Polimero

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

compositi

Powder impregnated tows(con polveri)

Fibre Impregnated Thermoplastic, FIT(in guaina)

Fibre preimpregnate

compositi

Pellets rinforzati

Fibra corta<1mm

Fibra lunga<1cm

Short and long fibres reinforced polymer pellets

compositi

LAVORAZIONE DEI COMPOSITI TERMOPLASTICI

Processi a 2 stadiProcessi 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

StampaggioLarge 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:

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):

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

Filament winding Pultrusion

Thermoforming Compression Moulding

compositi

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

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.

Reinforcement of profiles

compositi