Compositi a matrice termoplastica: perchй?

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

2
Matrici TP Rinforzo

• Fibre di vetro
• Fibre di carbonio
• aramidi, poliammidi
• poliesteri
• polietilene
• polipropilene

• HDPE
• PP
• ABS
• PA12
• PPE
• PEEK PPS

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.
4
Polichetoni
Cristallini (30), trasparenti buone proprietà
meccaniche Tg 143C, Tm 334C per parti
soggette ad alte temperature (240-280C) e in
mezzi aggressivi nei trasporti, reattori chimici
in elettronica
5
Poli(fenilen solfuro) PPS
Altamente cristallino (60), Tg 85C, Tm 285C
per usi in continuo a 200-240C, resistenti alla
fiamma, resistenti a acidi e basi ma meno agli
agenti ossidanti. Per apparecchiature in cucina,
nel settore automotive ed industriale
6
Applicazioni
Applicati specialmente per materiali leggeri ad
alte prestazioni Hanno buona resilienza
(resistenza allimpatto) e inerzia chimica
7

• racing bicycle components
• lifeboat
• antiballistic helm
• wing leading edge

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

9
(No Transcript)
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

11
Prepregs (fogli preimpregnati)
Via secca
Via umida
12
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
13
Fibre preimpregnate
Powder impregnated tows (con polveri)
Fibre Impregnated Thermoplastic, FIT (in guaina)
14
Short and long fibres reinforced polymer pellets
Fibra corta lt1mm
Pellets rinforzati
Fibra lunga lt1cm
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)

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.

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
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
19
Filament winding
Pultrusion
Thermoforming
Compression Moulding
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

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.
22
(No Transcript)