4
the efficiency of different amino compounds as formalde-
hyde trapping agents for free formaldehyde in phenolic
resin. The effects of different amino-formaldehyde trap-
ping agents the phenolic resin formaldehyde release, foam-
ing ratio, curing temperature, thermal stability, micro-pore
size, and other properties were studied and results are show
that the urea modified phenolic resin (PUF) had the high-
est formaldehyde removal efficiency. It had the lowest heat
release during combustion and the foam pore size was large
and uniform.
Over the past few decades, there have been attempts
to increase the toughness of phenolic foams (Mendelsohn
et al., 1979). Particularly, short fiber reinforcement of phe-
nolic foam was considered (Shen et al., 2003). Significant
improvements in peel strength and toughness were achieved
by reinforcing phenolic foam with aramid fibers (e.g.,
Nomex and/or Kevlar), which have well-known affinity for
phenolic foams. For example, Shen et al. found that the
addition of only 3 wt% short aramid fibers produced a six-
fold increase in peel strength, and addition of 5 wt% fibers
resulted in a seven-fold increase over unreinforced foams.
Furthermore, increasing the fiber length and the fiber load-
ing generally increased the toughness. Interestingly, aramid
fibers were more effective than glass fibers in enhancing the
peel strength and abrasion resistance for equivalent load-
ings and fiber length, while glass fiber additions enhanced
foam strength, stiffness, and dimensional stability (Shen
et al., 2003). The combined effect of Chopped Glass and
Aramid Fibers on physical properties of phenolic foams are
investigated in (Desai et al., 2008). Effect of microwaves on
the synthesis of phenolic resins is investigated in (Srivastava
et al., 2015). The study compared the mechanical proper-
ties of cast or resole-type phenolic resin systems. The res-
ins were cured at 100°C with 40% by weight of polyamide
using both traditional and microwave irradiation methods.
Mechanical properties such as tensile strength, elongation
at break, and impact strength were examined for the two
curing methods. The tensile strengths in the traditional
method ranged from 10.7 MPa to 16.8 MPa, while in
the microwave method, they ranged from 11.2 MPa to
17.5 MPa. Generally, samples cured by the microwave
method performed better in terms of tensile strength, indi-
cating that the microwave method can enhance polymeriza-
tion in resin systems and improve strength. The elongation
at break values for both methods are quite similar. In the
traditional method, the elongation at break ranged from
380% to 394%, while in the microwave method, it was
observed to range from 384% to 395%. Impact strength
varied between 1.3 kJ/m2 and 1.8 kJ/m2 in the traditional
method, whereas it was observed to range from 1.6 kJ/m2
to 2.1 kJ/m2 in the microwave method. The microwave
method provides an increase in impact strength. It can be
said that microwave irradiation strengthens the structure of
the polymers, thereby enhancing impact strength. In light
of all these results, it is suggested that microwave curing
could be a more efficient method for phenolic resin systems.
(X. Hu et al., 2016) investigated the effect of glass
fibers, nanoclay and their mixture on the mechanical prop-
erties of phenolic foams. The individual and combined
effects of glass fibers and nanoclay on the compressive and
impact strength of the phenolic foams are illustrated in
Figure 3. and Figure 4. respectively.
The glass fiber–nanoclay composite foams demonstrate
a good synergistic effect between glass fiber and nanoclay.
They could significantly increase the impact strength, com-
pression strength of the foams. The comprehensive com-
parison shows that when glass fiber and nanoclay are added
%5gf+%2
nc
%5gf+%3
nc
%5gf+%4
nc
0
0.05
0.1
0.15
0.2
0.25
0 5 10
Additive Content (%)
Glass_Fibers
Nanoclay
Glass_�iber&N
anoclay
Figure 3. Individual and combined effects of glass fibers and
nanoclay on the compressive strength on phenolic foams
%5gf+%2
nc
%5gf+%3
nc
%5gf+%4
nc
0
1
2
3
4
5
6
7
0 5 10
Additive Content (%)
Glass_�ibers
Nanoclay
Glass_�ibers&
Nanoclay
Figure 4. Individual and combined effects of glass fibers and
nanoclay on the impact strength on phenolic foams
Compressive
Strength(
a)
Impact
Strength(kJ.m-2)
the efficiency of different amino compounds as formalde-
hyde trapping agents for free formaldehyde in phenolic
resin. The effects of different amino-formaldehyde trap-
ping agents the phenolic resin formaldehyde release, foam-
ing ratio, curing temperature, thermal stability, micro-pore
size, and other properties were studied and results are show
that the urea modified phenolic resin (PUF) had the high-
est formaldehyde removal efficiency. It had the lowest heat
release during combustion and the foam pore size was large
and uniform.
Over the past few decades, there have been attempts
to increase the toughness of phenolic foams (Mendelsohn
et al., 1979). Particularly, short fiber reinforcement of phe-
nolic foam was considered (Shen et al., 2003). Significant
improvements in peel strength and toughness were achieved
by reinforcing phenolic foam with aramid fibers (e.g.,
Nomex and/or Kevlar), which have well-known affinity for
phenolic foams. For example, Shen et al. found that the
addition of only 3 wt% short aramid fibers produced a six-
fold increase in peel strength, and addition of 5 wt% fibers
resulted in a seven-fold increase over unreinforced foams.
Furthermore, increasing the fiber length and the fiber load-
ing generally increased the toughness. Interestingly, aramid
fibers were more effective than glass fibers in enhancing the
peel strength and abrasion resistance for equivalent load-
ings and fiber length, while glass fiber additions enhanced
foam strength, stiffness, and dimensional stability (Shen
et al., 2003). The combined effect of Chopped Glass and
Aramid Fibers on physical properties of phenolic foams are
investigated in (Desai et al., 2008). Effect of microwaves on
the synthesis of phenolic resins is investigated in (Srivastava
et al., 2015). The study compared the mechanical proper-
ties of cast or resole-type phenolic resin systems. The res-
ins were cured at 100°C with 40% by weight of polyamide
using both traditional and microwave irradiation methods.
Mechanical properties such as tensile strength, elongation
at break, and impact strength were examined for the two
curing methods. The tensile strengths in the traditional
method ranged from 10.7 MPa to 16.8 MPa, while in
the microwave method, they ranged from 11.2 MPa to
17.5 MPa. Generally, samples cured by the microwave
method performed better in terms of tensile strength, indi-
cating that the microwave method can enhance polymeriza-
tion in resin systems and improve strength. The elongation
at break values for both methods are quite similar. In the
traditional method, the elongation at break ranged from
380% to 394%, while in the microwave method, it was
observed to range from 384% to 395%. Impact strength
varied between 1.3 kJ/m2 and 1.8 kJ/m2 in the traditional
method, whereas it was observed to range from 1.6 kJ/m2
to 2.1 kJ/m2 in the microwave method. The microwave
method provides an increase in impact strength. It can be
said that microwave irradiation strengthens the structure of
the polymers, thereby enhancing impact strength. In light
of all these results, it is suggested that microwave curing
could be a more efficient method for phenolic resin systems.
(X. Hu et al., 2016) investigated the effect of glass
fibers, nanoclay and their mixture on the mechanical prop-
erties of phenolic foams. The individual and combined
effects of glass fibers and nanoclay on the compressive and
impact strength of the phenolic foams are illustrated in
Figure 3. and Figure 4. respectively.
The glass fiber–nanoclay composite foams demonstrate
a good synergistic effect between glass fiber and nanoclay.
They could significantly increase the impact strength, com-
pression strength of the foams. The comprehensive com-
parison shows that when glass fiber and nanoclay are added
%5gf+%2
nc
%5gf+%3
nc
%5gf+%4
nc
0
0.05
0.1
0.15
0.2
0.25
0 5 10
Additive Content (%)
Glass_Fibers
Nanoclay
Glass_�iber&N
anoclay
Figure 3. Individual and combined effects of glass fibers and
nanoclay on the compressive strength on phenolic foams
%5gf+%2
nc
%5gf+%3
nc
%5gf+%4
nc
0
1
2
3
4
5
6
7
0 5 10
Additive Content (%)
Glass_�ibers
Nanoclay
Glass_�ibers&
Nanoclay
Figure 4. Individual and combined effects of glass fibers and
nanoclay on the impact strength on phenolic foams
Compressive
Strength(
a)
Impact
Strength(kJ.m-2)