Compositi a matrice
termoplastica: perché?
Le resine termoindurenti sono fragili non possono essere rifuse o riformate.
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
•
•
•
•
•
•
HDPE
PP
ABS
PA12
PPE
PEEK PPS
Rinforzo
•
•
•
•
•
•
compositi
Fibre di vetro
Fibre di carbonio
aramidi, poliammidi
poliesteri
polietilene
polipropilene
Poli(fenilen etere) PPE
R
R
n
OH
O2, Cu cat
R
O
R
R
O H
+ n H2O
R
n
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
O
n HO
OH
n F
F
C
K2CO3
O
O
O
2n KF
C
n
PEEK
Cristallini (30%), trasparenti buone proprietà meccaniche
Tg 143°C, Tm 334°C per parti soggette ad alte temperature (240280°C) e in mezzi aggressivi nei trasporti, reattori chimici in
compositi
elettronica
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
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
producer:
Campagnolo
material:
Tepex carbon/PA6.6
production
volume:
production
> 100.000/year
process:
application
reasons:
weight, quality, cycle times,
automation, costs
producer:
Halmatic
material:
Twintex glass/PP
production
volume:
production
~ 500/year
process:
application
reasons:
cost, impact resistance, emission
harmful gasses
•racing bicycle components
high spead pressing
•lifeboat
vacuum moulding
producer:
Cato Composites
material:
TEPEX aramid/PA6
production
volume:
production
50.000/year
process:
application
reasons:
superior performance,
automation, cost
producer:
Fokker Special Products
material:
glass/PPS
production
volume:
production
< 100/year
process:
application
reasons:
stiffness/weight, reduction parts
number, cost
•antiballistic helm
high speed pressing
•wing leading edge
vacuum moulding
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
compositi
confronto a 0.2-2Pa.s. dei sistemi
termoindurenti).
COMPOSITI A MATRICIETERMOPLASTICA
Processing
Step 1
Commistione
di
Fibre
fogli
preimpregnati
fibre
preimpregnate
step 2
filato
filament winding,
pultusione
Stampaggio (a pressione)
Termoformatura
Tessuto
termoformatura
stampaggio
compositi
pellets
rinforzati
in guaina
fibra lunga (1 cm)
con polveri
fibra corta (1 mm)
In guaina:
filament winding
Fibra lunga:
stampaggio ad iniezione
Con polveri:
Poltrusione
Fibra corta:
Stampaggio a iniezione
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
Prepregs:
(fogli preimpregnati)
Via secca
Via umida
compositi
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
sezione
Filamento di Rinforzo
Filamento di Polimero
Fibre preimpregnate
Powder impregnated tows
(con polveri)
Fibre Impregnated Thermoplastic, FIT
(in guaina)
compositi
Short and long fibres reinforced polymer pellets
Fibra corta
<1mm
Pellets rinforzati
Fibra lunga
<1cm
compositi
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
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:
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 preimpregnated 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
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