3
studies. The effect of F/P ratio on the compressive strength
(CS) on phenolic foams is investigated in (X. M. Hu et al.,
2015). According to the research findings, as the F/P ratio
increases, the compressive strength also rises. Specifically,
as the F/P ratio increases from 1.0 to 2.4, the compressive
strength rises from approximately 0.8 MPa to 1.3 MPa. This
trend indicates that increasing the F/P ratio is an effective
method for enhancing the durability of phenolic foams. To
achieve the desired durability in phenolic foam production,
the F/P ratio can be increased to optimize the compressive
strength of the foam. However, the effects of a high F/P
ratio on other properties of the foam (such as flexibility or
fire resistance) should also be considered.
THE ENHANCEMENT ATTEMPTS
OF PHYSICAL AND MECHANICAL
PROPERTIES OF PHENOLIC FOAMS
Additive materials play a crucial role in enhancing or alter-
ing the physical and chemical properties of phenolic foams
and researchers are studied the effects of different type of
additive materials on the properties of phenolic foams.
Bio-Mass Addition
Phenolic foams are usually produced from petroleum-based
materials and increasing environmental concerns and fluc-
tuations in oil prices have driven research towards bio-based
alternatives such as lignin, tannin, cardanol and bio-oils.
Lignin can be described as a complex, aromatic and highly
branched heterogeneous polymer (Boerjan et al., 2003),
composed of multiple functional groups, such as hydroxyl
and methoxyl groups, along with a phenolic backbone.
(Londoño Zuluaga et al., 2018) investigated the possible
use of lignin as a raw material for phenolic foam produc-
tion. Firstly, direct utilization of lignin is investigated.
When the amount of lignin is increased, the mechanical
properties, such as the flexural and compressive strengths,
are negatively affected. The addition of lignin in foams
has resulted in a higher apparent density and compres-
sion strength compared with that of conventional phenolic
foams. However, studies have shown that increased substi-
tution rates do not result in a major improvement in the
thermal conductivity and fire-retardant properties. Lignin
derivatives have also been used in phenolic foams. For
example, lignin nanoparticles have been used as a filler and
achieved an 8.5% substitution rate for optimum mechani-
cal properties. Although the substitution rate is compara-
tively low, one of the benefits of lignin nanoparticles is the
reduction in the blowing agent amount without affecting
the mechanical performance (Del Saz-Orozco et al., 2015).
Secondly the modified versions of lignin used to pro-
duce phenolic foams and its effect on mechanical and
thermal properties are given. The compressive strength of
modified-lignin phenolic foams ranges from 0.09 MPa to
10 MPa. Density values for modified lignin foams range
from 28 kg/m3 to 66 kg/m3, which falls in the range of
standard density values for conventional foams (25 kg/m3
to 60 kg/m3). In (Weng et al., 2023), lignin material doped
with nitrogen and phosphorus and their effects on flame
retardancy and compressive strength of phenolic foams are
investigated. The results show that, as the lignin content
increases, both compression and flexural strengths initially
increase. The best mechanical performance was obtained
when the lignin content was 10%. Compared to pure
phenolic foam, compression strength increased by 63%
to 0.258 MPa and flexural strength increased by 291% to
0.801 MPa. This is related to the cell structure becoming
more homogeneous and stable, thus allowing better distri-
bution and absorption of external forces. However, when
the lignin content reaches 15%, the viscosity of the resin
increases excessively, which leads to insufficient homogene-
ity of the mixture during the foaming process. As a result,
the resulting foam cell structure is not homogeneous, its
ability to absorb external stresses decreases, and its mechan-
ical properties decrease. Therefore, optimum lignin content
is very important to obtain the best balance of compression
and flexural strength in phenolic foams.
In addittion (Sarika et al., 2021), Tannin-Based Foams
has Compressive Strength between 0.07–0.21 MPa,
Achieved LOI values above 40, indicating excellent flame
resistance. Cardanol-Based Foams has Compressive
Strength between 0.14–0.268 MPa and Flexural Strength
between 0.28–0.362 MPa, improved flexibility but require
phosphorus or silicon additives to enhance fire resis-
tance, Bio-Oil-Based Foams has Compressive Strength of
0.22 MPa, better flexibility and reduced brittleness com-
pared to standard phenolic foams.
Addition of Different Kind of Materials and Their
Observed Results
Phenolic resin has good flame retardant properties, foam-
ing properties and air tightness, which is widely used in the
field of mine air plugging. However, the traditional pheno-
lic resin prepolymer contains a large amount of free form-
aldehyde. The release of formaldehyde will seriously pollute
the construction environment and threaten the health of
workers. Therefore, the solution of formaldehyde pollu-
tion is of great significance for the application of phenolic
resin and its foam products in the field of coal mines fire
prevention and extinguishing. (Dong et al., 2023) studied
studies. The effect of F/P ratio on the compressive strength
(CS) on phenolic foams is investigated in (X. M. Hu et al.,
2015). According to the research findings, as the F/P ratio
increases, the compressive strength also rises. Specifically,
as the F/P ratio increases from 1.0 to 2.4, the compressive
strength rises from approximately 0.8 MPa to 1.3 MPa. This
trend indicates that increasing the F/P ratio is an effective
method for enhancing the durability of phenolic foams. To
achieve the desired durability in phenolic foam production,
the F/P ratio can be increased to optimize the compressive
strength of the foam. However, the effects of a high F/P
ratio on other properties of the foam (such as flexibility or
fire resistance) should also be considered.
THE ENHANCEMENT ATTEMPTS
OF PHYSICAL AND MECHANICAL
PROPERTIES OF PHENOLIC FOAMS
Additive materials play a crucial role in enhancing or alter-
ing the physical and chemical properties of phenolic foams
and researchers are studied the effects of different type of
additive materials on the properties of phenolic foams.
Bio-Mass Addition
Phenolic foams are usually produced from petroleum-based
materials and increasing environmental concerns and fluc-
tuations in oil prices have driven research towards bio-based
alternatives such as lignin, tannin, cardanol and bio-oils.
Lignin can be described as a complex, aromatic and highly
branched heterogeneous polymer (Boerjan et al., 2003),
composed of multiple functional groups, such as hydroxyl
and methoxyl groups, along with a phenolic backbone.
(Londoño Zuluaga et al., 2018) investigated the possible
use of lignin as a raw material for phenolic foam produc-
tion. Firstly, direct utilization of lignin is investigated.
When the amount of lignin is increased, the mechanical
properties, such as the flexural and compressive strengths,
are negatively affected. The addition of lignin in foams
has resulted in a higher apparent density and compres-
sion strength compared with that of conventional phenolic
foams. However, studies have shown that increased substi-
tution rates do not result in a major improvement in the
thermal conductivity and fire-retardant properties. Lignin
derivatives have also been used in phenolic foams. For
example, lignin nanoparticles have been used as a filler and
achieved an 8.5% substitution rate for optimum mechani-
cal properties. Although the substitution rate is compara-
tively low, one of the benefits of lignin nanoparticles is the
reduction in the blowing agent amount without affecting
the mechanical performance (Del Saz-Orozco et al., 2015).
Secondly the modified versions of lignin used to pro-
duce phenolic foams and its effect on mechanical and
thermal properties are given. The compressive strength of
modified-lignin phenolic foams ranges from 0.09 MPa to
10 MPa. Density values for modified lignin foams range
from 28 kg/m3 to 66 kg/m3, which falls in the range of
standard density values for conventional foams (25 kg/m3
to 60 kg/m3). In (Weng et al., 2023), lignin material doped
with nitrogen and phosphorus and their effects on flame
retardancy and compressive strength of phenolic foams are
investigated. The results show that, as the lignin content
increases, both compression and flexural strengths initially
increase. The best mechanical performance was obtained
when the lignin content was 10%. Compared to pure
phenolic foam, compression strength increased by 63%
to 0.258 MPa and flexural strength increased by 291% to
0.801 MPa. This is related to the cell structure becoming
more homogeneous and stable, thus allowing better distri-
bution and absorption of external forces. However, when
the lignin content reaches 15%, the viscosity of the resin
increases excessively, which leads to insufficient homogene-
ity of the mixture during the foaming process. As a result,
the resulting foam cell structure is not homogeneous, its
ability to absorb external stresses decreases, and its mechan-
ical properties decrease. Therefore, optimum lignin content
is very important to obtain the best balance of compression
and flexural strength in phenolic foams.
In addittion (Sarika et al., 2021), Tannin-Based Foams
has Compressive Strength between 0.07–0.21 MPa,
Achieved LOI values above 40, indicating excellent flame
resistance. Cardanol-Based Foams has Compressive
Strength between 0.14–0.268 MPa and Flexural Strength
between 0.28–0.362 MPa, improved flexibility but require
phosphorus or silicon additives to enhance fire resis-
tance, Bio-Oil-Based Foams has Compressive Strength of
0.22 MPa, better flexibility and reduced brittleness com-
pared to standard phenolic foams.
Addition of Different Kind of Materials and Their
Observed Results
Phenolic resin has good flame retardant properties, foam-
ing properties and air tightness, which is widely used in the
field of mine air plugging. However, the traditional pheno-
lic resin prepolymer contains a large amount of free form-
aldehyde. The release of formaldehyde will seriously pollute
the construction environment and threaten the health of
workers. Therefore, the solution of formaldehyde pollu-
tion is of great significance for the application of phenolic
resin and its foam products in the field of coal mines fire
prevention and extinguishing. (Dong et al., 2023) studied