A low concentrated polystyrene (PS) additive to epoxy is used, since it is able to reduce the curing reaction rate but not at the cost of increasing viscosity and decreasing glass transition temperature of the curing epoxy. The modified epoxy is cocured with a compatible thermoplastic interleaf during the vacuum assisted resin transfer molding (VARTM) to toughen the interlaminar of the composites. Using viscometry, the solubilities of thermoplastics (TPs) polycarbonate (PC), polyetherimide (PEI), and polysulfone (PSU) are determined to predict their compatibility with epoxy. The diffusion and precipitation process between the most compatible polymer PSU and epoxy formed semi-interpenetration networks (semi-IPN). To optimize bonding adhesion, these diffusion and precipitation regions were studied via optical microscopy under curing temperatures from 25 °C to 120 °C and PS additive concentrations to epoxy of 0–5%. Uniaxial tensile tests were performed to quantify the effects of diffusion and precipitation regions on composite delamination resistance and toughness. Crack paths were observed to characterize crack propagation and arrest mechanism. Fracture surfaces were examined by scanning electron microscopy (SEM) to characterize the toughening mechanism of the thermoplastic interleaf reinforcements. The chemically etched interface between diffusion and precipitation regions showed semi-IPN morphology at different curing temperatures. Results revealed deeper diffusion and precipitation regions increase energy required to break semi-IPN for crack propagation resulting in crack arrests and improved toughness.

References

References
1.
Shetty
,
R. R.
,
Pavithra
,
G. K.
, and
Rai
,
S. K.
,
2013
, “
Studies on Mechanical and Fractographic Behavior of Polycarbonate-Toughened Epoxy-Granite Particle Hybrid Composites
,”
Polym. Plast. Technol. Eng.
,
52
(
11
), pp.
1122
1126
.
2.
Jin
,
Z.
,
Tong
,
L.
, and
Xungai
,
W.
,
2010
, “
Electrospun Nanofiber Toughened Carbon/Epoxy Composites: Effects of Polyetherketone Cardo (PEK-C) Nanofiber Diameter and Interlayer Thickness
,”
Compos. Sci. Technol.
,
70
(11), pp.
1660
1666
.
3.
Xu
,
Y.
,
Liao
,
G.
,
Gu
,
T.
,
Zheng
,
L.
, and
Jian
,
X.
,
2008
, “
Mechanical and Morphological Properties of Epoxy Resins Modified by Poly(Phthalazinone Ether Sulfone Ketone)
,”
J. Appl. Polym. Sci.
,
110
(
4
), pp.
2253
2260
.
4.
Martines
,
I.
,
Martin
,
M. D.
,
Eceiza
,
A.
,
Oyanguren
,
P.
, and
Mondragon
,
I.
,
2000
, “
Phase Separation in Polysolfune-Modified Epoxy Mixtures. Relationships Between Curing Conditions, Morphology and Ultimate Behavior
,”
Polymer
,
41
(
3
), pp.
1027
1035
.
5.
Blanco
,
I.
,
Cicala
,
G.
, and
Faro
,
C. L.
,
2003
, “
Improvement of Thermomechanical Properties of a DGEBS/DDS System Blended With a Novel Thermoplastic Copolymer by Realization of a Semi-IPN Network
,”
J. Appl. Polym. Sci.
,
88
(
13
), pp.
3021
3025
.
6.
Heitzmann
,
M. T.
,
Hou
,
M.
,
Verdt
, V
. M.
,
Vandi
,
L.
, and
Paton
,
R.
,
2013
, “
Morphology of an Interface Between Polyetherimide and Epoxy Prepreg
,”
Adv. Mater. Res.
,
393–395
, pp. 184–188.
7.
Tan
,
H.
, and
Yao
,
Y. L.
,
2013
, “
Laser Joining of Continuous Glass Fiber Composite Preforms
,”
ASME J. Manuf. Sci. Eng.
,
135
(
1
), p.
011010
.
8.
Bian
,
D. K.
,
Satoh
,
G.
, and
Yao
,
Y. L.
,
2015
, “
The Laser Interlaminar Reinforcement of Continuous Glass Fiber Composites
,”
ASME J. Manuf. Sci. Eng.
,
137
(
6
), p.
061001
.
9.
Groleau
,
M. R.
,
Shi
,
Y. B.
,
Yee
,
A. F.
,
Bertram
,
J. L.
,
Sue
,
H. J.
, and
Yang
,
P. C.
,
1996
, “
Mode II Fracture of Composites Interleafed With Nylon Particles
,”
Compos. Sci. Technol.
,
56
(
11
), pp.
1223
1240
.
10.
Hillermeier
,
R. W.
, and
Sefeis
,
J. C.
,
2001
, “
Interleaf Toughening of Resin Transfer Molding Composites
,”
Composites, Part A
,
32
(
5
), pp.
721
729
.
11.
Li
,
G.
,
Li
,
P.
,
Zhang
,
C.
,
Liu
,
Y. H.
,
Zhang
,
H. Y.
,
Jia
,
X. L.
,
Yang
,
X. P.
,
Xue
,
Z. M.
, and
Ryu
,
S. K.
,
2008
, “
Inhomogeneous Toughening of Carbon Fiber/Epoxy Composite Using Electrospun Polysulfone Nanofibrous Membranes by In Situ Phase Separation
,”
Compos. Sci. Technol.
,
68
, pp.
987
994
.
12.
Kuwata
,
W.
, and
Hogg
,
P. J.
,
2011
, “
Interlaminar Toughness of Interleaved CFRP Using Non-Woven Veils
,”
Composites, Part A
,
42
(
10
), pp.
1551
1570
.
13.
Tan
,
H.
, and
Yao
,
Y. L.
,
2013
, “
Feasibility Analysis of Inter-Laminar Toughening for Improving Delamination Resistance
,”
Manuf. Lett.
,
1
(
1
), pp.
33
37
.
14.
Bian
,
D. K.
,
Bucher
,
T.
,
Shim
,
D. J.
,
Jones
,
M.
, and
Yao
,
Y. L.
,
2016
, “
Effect of Deep Penetration of Interleaf on Delamination Resistance in GFRP
,”
J. Manuf. Sci. Technol.
,
138
(
7
), p.
071011
.
15.
Mangaraj
,
D.
,
Bhatnagar
,
S. K.
, and
Rath
,
S. B.
,
1963
, “
Cohesive-Energy-Density of High Polymers Part III: Estimation of C.E.D by Viscosity Measurement
,”
Macromol. Chem. Phys.
,
67
(
1
), pp.
75
83
.
16.
Bernard
,
L.
,
Chapel
,
J. P.
, and
Gernard
,
J. F.
,
2001
, “
Gradient Interphase Between Reactive Epoxy and Glassy Thermoplastic From Precipitation Process, Reaction Kinetics and Phase Separation Thermodynamics
,”
Macromolecules
,
34
(5), pp.
1204
1213
.
17.
Gyunn
,
N.
,
Yong
,
Y.
,
Won
,
G.
, and
Kim
,
S. C.
,
2004
, “
Toughening of Epoxy Composite by Dispersing Polysulfone Particle to Form Morphology Spectrum
,”
Polym. Bull.
,
52
(5), pp.
365
372
.
18.
Gyunn
,
N.
,
Yong
,
Y.
,
Won
,
G.
, and
Kim
,
S. C.
,
2004
, “
Toughening of Carbon Fiber/Epoxy Composite by Inserting Polysulfone Film to Form Morphology Spectrum
,”
Polymer
,
45
, pp.
6953
6958
.
19.
Gan
,
W. J.
,
Yu
,
Y. F.
, and
Liu
,
X. Y.
,
2009
, “
Kinetics of Phase Separation at the Early Stage of Spinodal Decomposition in Epoxy Resin Modified With PEI Blends
,”
Colloid Polym. Sci.
,
287
(
1
), pp.
23
28
.
20.
Rico
,
J. L.
,
Montero
,
B.
,
Diez
,
J.
, and
Ramirez
,
C.
,
2009
, “
Polymer Blends Based on an Epoxy-Amine Thermoset and a Thermoplastic: Effect of Thermoplastic on Cure Reaction and Thermal Stability of the System
,”
J. Therm. Anal. Calorim.
,
95
(
2
), pp.
369
376
.
21.
Brewer
,
J. C.
, and
Lagece
,
P. A.
,
1988
, “
Quadratic Stress Criterion for Initiation of Delamination
,”
J. Compos. Mater.
,
22
(
12
), pp.
1141
1155
.
22.
Aksoy
,
A.
, and
Carlsson
,
L. A.
,
1991
, “
Crack Tip Yield Zone Estimates in Mode II Interlaminar Fracture of Interleaved Composites
,”
Eng. Fract. Mech.
,
39
(
3
), pp.
525
534
.
23.
Woods
,
J.
,
Modin
,
A. E.
,
Hawkins
,
R. D.
, and
Hanks
,
D. J.
,
2002
, “
Controlled Atmospheric Pressure Infusion Process
,” International Patent No. WO 03/101708 A1.
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