Scientific African 19 (2023) e01501 
Contents lists available at ScienceDirect 
Scientific African 
journal homepage: www.elsevier.com/locate/sciaf 
A systematic study of the effect of graphene oxide and 
re duce d graphene oxide on the thermal degradation behavior 
of acrylonitrile-butadiene rubber in air and nitrogen media 
Bismark Mensaha , ∗ , David Sasu Konadua ,  Frank Nsafulb ,  
Prosper Naah Angnunavuri c ,  Samuel Kwofied  
a Department of Materials Science and Engineering, CBAS, University of Ghana, Legon, Ghana 
b Department of Food Processing and Engineering, CBAS, University of Ghana, Legon, Ghana 
c School of Engineering, Department of Civil and Environmental Engineering, University of Energy and Natural Resources, Sunyani, Ghana 
d Ghana Gas Company limited 
a r t i c l e i n f o a b s t r a c t 
Article history: Thermal degradation of acrylonitrile-butadiene rubber (NBR)-graphene oxide (GO)/reduced 
Received 14 October 2022 graphene Oxide (G) composites (NBR-GO/G) was studied in air O 2(g) and nitrogen N  2(g)  
Revised 8 December 2022 media at ∼800 °C, using Thermal Gravimetric Analysis (TGA/DTG). The char yield of the 
Accepted 10 December 2022 
composites was high the in N 2(g) medium. This was associated with lower weight loss (%)  
and higher maximum degradation temperatures, T max( °C). Doyle simple kinetic approach  
Editor DR B Gyampoh was used for the first time to estimate the degradation kinetics of the NBR-GO/G com-     
posites and large amounts of activation energy E a (KJ/mol) was observed, particularly for  
Keywords: 
the NBR-GO composites. In O 2(g) medium, severe degradation of NBR occurred irrespec-  
Acrylonitrile-butadiene rubber 
tive of the GO/G-filler content. This suggested that insignificant char yield was produced 
Graphene and derivative graphene sheets 
(GDS) to protect the scission of the NBR backbone, as decomposition of the main chain seemed  
G graphene oxide (GO) and reduced to have been accelerated by the high oxygenated moieties (C–O–C, –O–C = O and O–H) dec-       
graphene Oxide (G) orating GO/G-sheets. For instance, NBR showed ∼89, ∼21 and ∼86 % weight residue, W    r 
Thermal degradation (%) than G 0.1, G 0.5 and G 1 respectively and ∼154, ∼350, ∼92 % higher than the respec-    
Maximum degradation temperatures tive GO 0.1, GO 0.5 and GO 1 samples. Although, NBR-G recorded higher W r(%) than NBR-GO,     
Thermal degradation kinetics NBR-GO generally slowed the degradation of NBR than NBR-G composites, possibly due 
to the presence of high concentration of interactions (NBR—S x—GO—S—NBR and NBR— 
O—Hσ+  —N σ− —C—NBR) which raised the E a (KJ/mol) barrier for decomposition. The high  
thermal stability and compression set (%) properties of NBR-GO/G composites obtained as 
compared to pure NBR indicated that solution processing techniques used in this current 
work was very effective than those compounded with melt mixing methods or with GO/G- 
functionalized nanoparticles. Therefore, this present study provides insights on tailoring 
rubber-graphene based materials for thermally harsh and high pressure applications such 
as; oil/gas drilling hose, oil/gas seals, gasket and tire tread materials. 
© 2022 The Authors. Published by Elsevier B.V. on behalf of African Institute of 
Mathematical Sciences / Next Einstein Initiative. 
This is an open access article under the CC BY license 
( http://creativecommons.org/licenses/by/4.0/ ) ∗ Corresponding author. 
E-mail address: bismarkmensah@ug.edu.gh (B. Mensah) . 
https://doi.org/10.1016/j.sciaf.2022.e01501 
2468-2276/© 2022 The Authors. Published by Elsevier B.V. on behalf of African Institute of Mathematical Sciences / Next Einstein Initiative. This is an 
open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ ) 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Introduction 
The viscoelastic nature of rubbers render them as promising materials in the polymer industry for various applications in- 
cluding high deformation (flexible/stretchable) sensors [1–6] , structural materials [7–9] , flame retardants [ 10 , 11 ] and thermal
insulating materials [12–14] . The long-term usages with safety guarantee for applications in high temperature environments 
are mostly focused on the development of synergy systems, comprising of the rubber matrix and desired content of rein- 
forcements like; metal oxides [14] , nanoclays [15–17] , carbon nanotubes [ 18 , 19 ], boron nitride nanotubes [20] and carbon
blacks [ 21 , 22 ]. Successful tailor-made elastomeric-filler composite products are able to delay the rapid thermal degradation 
of the bulk matrix due to successful dispersions of the fillers and the strong matrix-filler interactions [ 20 , 23-25 ]. 
The emergence of graphene and derivative graphene sheets (GDS) has already created a tremendous revolution in rubber- 
Nano-Technology [26–28] . This is due to the unique properties of the GDS, which include; high Young’s modulus of ∼1
TPa, excellent mechanical strength, high thermal conductivity of ∼50 0 0 W/(m K) and unparalleled electrical conductivity of 
∼60 0 0 S/cm [ 29 , 30 ]. By careful engineering, GDS can transfer some of these unique properties to the almost useless virgin
elastomeric matrix [26–28] . A lot of work on elastomer-GDS composites research has been reported with several property 
enhancements [ 7 , 26 , 27 ]. Greater portion of these studies have focused more on curing [31–33] , reinforcement/mechanical
strength [ 28 , 34-36 ], barrier properties [ 8 , 37 , 38 ], thermal conductivity [ 28 , 39-41 ] with few studies on thermal degradation
behaviors [ 25 , 41 ]. 
On thermal degradation studies, thermal gravimetric analysis (TGA) and the derivative thermal gravimetric analysis (DTG) 
have been widely used to estimate the thermal decomposition of rubber-GDS-based systems. When Dong et al. [25] rein- 
forced natural rubber (NR) with only 1.1 part per hundred of rubber (phr) graphene, the weight residue (%) derived from
the TGA curves for the NR-graphene was higher than that of pure NR. Other studies have focused on improving the thermal
degradation resistance of elastomers by functionalization of the GDS before incorporating them into the matrix [ 26 , 28 ]. For
example, Xiong et al. [41] functionalized graphene oxide (GO) with ionic liquid and incorporated it into bromo-isobutylene 
isoprene rubber (BIIR), an enhancement in thermal degradation resistances were observed as compared to the pure BIIR. 
Also, improvement in thermal degradation stability of carboxylated acrylonitrile-butadiene rubber (NBR)-GO composites was 
observed by Manna et al. [42] after functionalization of GO with hexadecyl amine (HDA). 
Moreover, it has been observed that the majority of thermal decomposition studies of rubber-GDS composites were done 
in N 2(g) medium and the kinetic energies of decomposition were calculated based on Ozawa and Kissinger et al. [43– 
45] approaches. Although, thermal stability of silicone rubber in only air O 2(g) medium was recently reported by Wang 
et al. [35] . It was observed that thermal degradation behavior of the composites depended greatly on size effect, that is, the
middle-size G obtained the best compared to the small or large-sized GO and G. 
Furthermore, Mensah et al. [46] earlier conducted a study on the curing, tensile and thermal stability (in N 2(g) medium) 
behavior of NBR-GO composites. It was observed that increasing GO content improved the tensile properties and shielded 
the NBR matrix from further decomposition. Thus, it can clearly be ascertained that the thermal degradation behavior of 
rubber-GDS based systems may be dependent on several factors including; type of GDS, chemistry of GDS, thermal con- 
ductivity, particle size, dispersions of the GDS, the characteristics of the matrix used as well as the medium in which the
thermal degradation study was carried [ 28 , 39-41 ]. 
Therefore, with these shortfalls in rubber-GDS research and together with global demand of multifunctional of materials, 
further works on the thermal degradation behavior of rubber reinforced with different rubber matrix and GDS types, par- 
ticularly in different decomposition environments like nitrogen, N 2(g) and air O 2(g) media etc., are worth exploring. In this  
present work, we prepare a composite of NBR reinforced with GO and G-nanosheets and investigate the curing, network 
density and compression set, CS (%) properties. The thermal degradation kinetics of the NBR-GO/G composites were studied 
separately in N 2(g) and air O 2(g) media by using TGA/DTG and Doyle method [ 47 , 48 ]. The results obtained provide insights  
on the need to select and design appropriate rubber matrix and GDS for thermally harsh and high pressure environments. 
Experimental 
Materials 
The base rubber matrix used is acrylonitrile-butadiene rubber (NBR) with the trade name KNB 25LMTM  , and acrylonitrile 
content (ACN) of 20-30%. The NBR was supplied by the Kumho Petrochemical Company, Korea. The vulcanization ingredients; 
zinc oxide (ZnO), stearic acid (SA), sulfur (S), and N-cyclohexile 2-benzotiazole sulfonamide (CZ) were all obtained from 
Intelligent Polymer Nano Lab (IPNL), Polymer Nano-technology Department, Jeonbuk National University, South Korea. The 
graphene oxide (GO) was synthesized from natural graphite (GRT) powder by using the modified Hummer’s method [ 49 , 50 ],
where GRT was oxidized and later exfoliated by ultra-sonication. Some amount of the GO was weighed and reduced into 
reduced graphene oxide (G), which is close to pristine graphene [ 26 , 50 ]. The reduction was done by using desired amount
of hydrazine (N 2H 4) and NH 4OH. The detailed synthesis method for the production of GO and G and characterizations done   
on GO and G were reported earlier by Mensah et al. [50] . 2 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Sample design and preparation 
The compound formulation expressed as parts per hundred of rubber (phr) with their corresponding codes are presented 
in Table I. The preparation of the NBR, and NBR-GO/G-composites nanocomposite was effectively attained by combined 
method of solution mixing and open two-roll milling [ 46 , 51 ]. Briefly, the NBR was cut into pieces and dissolved in solvent
(acetone) under 60 °C temperatures for ∼12 h. 
The GO and G were separately dispersed homogeneously in dimethylfuran (DMF) by prolonged ultrasonication for ∼2.5 
h, in order to separate the sheets from each other. The solutions of GO/DMF and G/DMF were each mixed with NBR/acetone
mixture separately. The mixtures were then stirred vigorously on a magnetic stirrer at ∼60 °C for ∼12 h until a homogenous
mixture of the composition was obtained. To avoid phase separation between the matrix and the GO/G-sheets, de-ionized 
water was added to the homogeneous mixture while still stirring. The resulting composites (NBR-GO and NBR-G) were oven 
dried at ∼80 °C for about ∼6 h, so as to eliminate entrapped liquid from the mixtures. Using a two-roll mill (Farrel 8422,
USA), the curing materials (ZnO, SA, CZ, and S) were gradually added one by one and combined to obtain solid masses.
The homogeneously milled samples were sheeted out and allowed to cool overnight. The various formulations were cured 
in a metallic square mold of dimension (15 cm x 15 cm) with ∼0.1 cm thickness in-between Mylar film, using a hot press
machine (Caver WMV50H, USA), at the optimum cure conditions. A pressure of ∼11 MPa and a temperature of 160 °C were
used as optimum cure conditions in the hot-pressing process. After allowing the cured samples to cool overnight, they were 
cut into standard shapes for further analysis and characterizations. 
Characterization 
Vulcanization properties 
The curing properties of the various compounds; NBR and NBR-GO/G composites, were investigated using an oscillating 
die cure rheometer (ODR) machine procured from IPNL, JBNU, South Korea, to identify the optimum cure time at 160 °C
using about ∼9-10 g of each sample. The various curing parameters of the various compounds were acquired from the 
rheo-curves, analyzed, and reported. The properties include; maximum torque (M H), minimum torque (M L), change in torque   
( M = M H - M  L), onset of cure time (t s2), optimal cure time (t 90), and curing rate index (CRI = 100/(t 90-t s2)).      
Scanning electron microscopy (SEM) 
The morphologies of the GO and G powders, NBR, and NBR-GO/G composites were observed by using SEM technique. 
The composites were first cryogenically fractured before being sputter-coated with platinum to increase their electrical con- 
ductivity at the observing surfaces. Field emission SEM/energy dispersive x-ray spectroscopy (EDS) (JEOL, JSM 599, Japan) 
was used to examine the surface morphologies including identification of elements in the various materials. The test was 
achieved within ∼40 min. 
Transmission electron microscopy (TEM) 
Ultrathin specimen (thinner than 100 nm) for TEM observation were cryogenically cut with a diamond knife using an 
ultrathin microtome (UCT, Leica Ultracut, EMFC7) and collected on 200-mesh copper grids. A transmission electron micro- 
scope was used to observe the exfoliation of GO and G-sheet nanosheets in NBR rubber (TEM, JEOL, JEM2100). The TEM
machine was used to observe exfoliated DMF/GO and DMF/G solutions that were dropped on the mesh separately. 
Crosslinking density by equilibrium swelling test 
By equilibrating the produced samples in methyl-ethyl ketone (MEK) (molar volume of 89.6 mL/mol) for ∼72 hours 
at room temperature, the equilibrium swelling of the vulcanized NBR and NBR-GO/NBR-G composites was evaluated. The 
degree of swelling (Q r) was calculated using the absorbed amount of MEK (W s-W   i) and the dried weight (W dr) of samples  
by using Eq. (1) . 
Q r = (W s −W ) /W (1)   i dr 
where, W i and W s are the initial and final weights of (NBR, NBR-GO and NBR-G) before and after swelling. The cross-linking  
density N c (mol/cm
3 
 ) of the vulcanizates was calculated by using Flory–Rehner model [52] in Eq. (2) . 
 
n c = −[ ln (1− v ) 2 1 / 3     + v + χ v ] / v (v − v / 2) (2)  2 2 1 2 1 2  2 
where, v 2 is the volume fraction of polymer in swollen gel at equilibrium, which is given as 1/ Q r. The v 1 is a molar vol-   
ume of swelling media (MEK). The interaction parameter ( χ1) between MEK and NBR was calculated to be 0.384, where 
the solubility parameters ( δ) of NBR ( δp) and MEK ( δs) was 8.9 cal1/2 −3/2   /cm and 9.27 cal1/2 /cm−3/2    respectively, by using  
Bristow–Watson [53] Eq. (3) ; 
χ1 = β + 2 1  (v 1/RT ) (δs − δp) (3)      3
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
Fig. 1. TGA curves based on integral procedural degradation temperature (IPDT) approach. 
 
 
 
 
 
 
 
 
where, R, T, and β1, are universal gas constant (8.314 J/mol K), absolute temperature, and lattice constant (usually about  
0.34). 
Compression set properties 
The compression set CS (%) of the vulcanized NBR and NBR-GO/G composites were determined according to ASTM D 395, 
same with the approach earlier reported by GS et al. [54] by using cylindrical specimens ( ∼12.5 mm height and ∼29 mm
diameter) and by applying a 25 % compression. Initially, the samples average heights were measured using caliper and were 
then kept in an air oven at the testing temperatures of 25, 50, 100 and 200 °C respectively, each for 72 h. The samples were
later taken out of the oven and allowed to cool at room temperature for ∼30 min. The final height was then measured and
the compression set CS (%) was calculated using the Eq. (4) ; 
CS (% = (H − H ) / (H − H ) (4)  ) o f o s  
where H o and H f are the initial and final height of the specimen and H s ( ∼9.5 mm) is the height of the spacer bar used.    
Thermal degradation and kinetics study 
DSC-TGA (TA Instrument, SDT Q600 V20.9 Build 20, USA) was used to study the thermal degradation behavior of the 
GO/G-sheets, and their compounds with NBR. The conditions were nitrogen and oxygen atmosphere, equilibrium temper- 
ature of ∼30 °C and heating rate of 10 °C/min to a maximum temperature of ∼800 °C. The thermal stability behavior of
NBR and NBR-GO/G-composites were studied based on the maximum degradation temperature (T max) from the derivative  
thermograph (DTG), weight residue (%) from the TGA curves, initial degradation temperature (IDT) and final degradation 
temperature (FDT). Later, the Doyle approach [ 47 , 48 ], where the integral procedural degradation temperature (IPDT) which
correlates with the volatile parts of the polymeric materials, and widely used to evaluate the overall inherent thermal sta- 
bility of polymeric materials in the degradation process, was also adopted for the first time in this present work to study
the thermal degradation kinetics behavior of NBR-GO/G composites in air and nitrogen media. The IPDT is usually estimated 
from the TGA curves using the following ∗ Eq. (5 - 7 ), where A is the area ratio of the total area of the experimental curve
divided by the total TGA curve, K∗ is the coefficient, T i is the initial experimental temperature ( ∼30 °C in this study), and T  f 
is the final experimental temperature ( ∼800 °C). S 1, S 2, and S 3 are the areas of the three regions into which the TGA plot   
had been divided, as shown in Fig. 1 below. 
( )
IP DT = A∗   K∗ T f − T i + T i (5)    
∗ = (S 1 + S   2)  A  + + (6) (S 1  S 2  S    3)  
∗ = (S 1 + S   2)  K  (7) 
(S  1)  4 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
Fig. 2. SEM analysis of (a) GO-sheets and (b) G-sheets (c) TEM image of GO-sheets and (d) TEM image of G-sheets. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Results and discussions 
Characterization of GO/G sheets: structure and morphology 
The SEM morphology of GO and G-sheets are clearly presented in Fig. 2 (a) and Fig. 2 (b), respectively. Layered crystalline
formations exist in graphite (interlayer spacing of ∼0.34 nm) [55–58] . In comparison to G-sheets ( Fig. 2 b), Fig. 2 a shows that
when graphite is oxidized and exfoliated into GO sheets, evidence of some of the sheets appearing to be severely corrugated 
or deformed are seen. 
The G-sheets seems to be relatively solid, with minimal wrinkling effects and exhibiting tendencies of the presence 
of crystalline impurities. Based on the SEM scale, the average thickness of the GO/G sheets was estimated to be ∼0.5-
4 nm. The wrinkling and corrugating structures of GO is shown in the TEM image ( Fig. 2 c) while the restoration of the
wrinkled structure of GO into G-sheets was achieved by using hydrazine (N 2H 4) and NH 4OH [ 49 , 59 ]. As seen in the TEM   
image in Fig. 2 d, by using the given TEM scale bar, GO and G-sheets show an estimated average thickness of ∼0.83-5 nm
with hydrodynamic lengths of ∼9-150 nm, measured by dynamic light scattering, as reported recently in the other work 
of Mensah et al. [60] . The structure and morphological features of GO/G-sheets in the SEM and TEM images are consistent
with those earlier reported [ 26 , 58 , 61-63 ], which confirms GO/G-sheets as nanoparticles. 
Thermal degradation behavior of GO/G-sheets 
The Fig. 3 is the TGA curves for the powdered nanoparticles of GO and G. The initial T onset ( °C) and final T max ( °C)  
degradation temperatures were taken at 10 and 90 % weight loss (%) respectively. The T onset ( °C) of GO and G sheets were 
observed at ∼93.4 and ∼198.5 °C respectively, while the T max ( °C) of GO and G was seen around ∼796.4 and ∼677 °C re- 
spectively. The initial degradation of GO and G may be ascribed to the evaporation of CO, CO 2 and water moisture from 
the sheets. The weight residue (%) of GO and G-sheets, after major decomposition at 800 °C was ∼48 % and ∼70 % respec-
tively. Thus, a higher temperature was required to decompose tight polar groups on GO-sheets, which consequently led 
to higher weight loss compared to G-sheets. The G-sheets although required lower temperature to be decomposed, yet in 
comparison to GO sheets, decomposition of G-sheets results in an increase in char yield, which delayed and protected the 
sheets from further breakdown. As earlier reported [ 32 , 51 , 64 ], the reduced oxygen concentration of G-sheets contributes to
their thermal breakdown stability improvement. G-sheets have also been shown to possess better thermal stability than GO- 
sheets, owing to their capacity to recover from corrugating and wrinkling structures through the reduction process of GO 
[ 25 , 27 , 65 ]. Meanwhile, detailed characterization of these same fillers (GO and G-sheets) which include; UV-vis spectroscopy,5 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
Fig. 3. TGA curves for GO and G-sheets 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Raman spectroscopy, x-ray photoelectric spectroscopy (XPS) analysis, FT-IR etc. was reported by Mensah et al. [50] and all 
the properties observed for the GO and G-sheets were in accordance with those reported in literature [ 26 , 4 9 , 57 , 66-6 8 ]. 
Characterization of NBR-GO/G composites 
Vulcanization behavior 
The vulcanization properties which include; scorch time (t s2), optimum cure time (t 90), minimum and maximum torque   
(M L & M H) and strength index (M = M   H −M  L) of NBR, loaded with variable amount (0.1 ∼1 phr) of GO and G fillers are 
plotted in Fig. 4 (a-d). In the presence of GO or G-sheets, the t s2 of the composites extended more than the pure NBR. 
The NBR-GO composites showed much longer t s2 than NBR-G systems. For processing stability and safety of the rubber and 
its final product, longer t s2 may be appreciable [ 26 , 32 , 69 ]. However, properties like the acidic nature of the GO/G-sheets, 
the chemistry of the GO/G sheets [ 26 , 27 , 32 ], the physical structure of the sheets (degree of wrinkling/corrugation of the
sheets) [ 26 , 62 , 63 , 70 ], thermal properties [ 25 , 58 , 71 ] of the sheets, as well as the viscosity of the matrix, are all factors that
may contribute to the extension of t s2 and t 90 of rubber-GDS composites [ 26 , 32 , 69 ]. As the GO/G-sheets were incorporated  
into the NBR matrix, the cure rate index (CRI) of the composites was increased as compared to the gum (NBR). The NBR-G
composites outperformed the NBR-GO systems. 
In terms of polarity, the curing properties of NBR-GO/G were better than that of non-polar ethylene-propylene-diene 
monomer (EPDM) systems, owing to their unsaturated sites (ENB) of EPDM [ 60 , 72-74 ]. In addition, when GO/G was added to
the NBR matrix, the rheological mechanical strength indices; viscosity (M L), crosslink density ( M) and mechanical strength  
(M H) of the composites were improved as compared to gum. This was supposed to be due to the creation of tighter network 
structures like; NBR–S x–G–S–NBR or NBR–S x–GO–S–NBR between the oxygen groups (C–O–C, –O–C = O and O–H) on the   
GO/G-sheets and the NBR matrix, as depicted in Fig. 5 . 
A physical interaction between the O −H of the GO/G-sheets and the nitrile group ( −C≡ N) of NBR through hydrogen
bonding was previously observed [ 26 , 32 ]. Thus, the homogenous dispersions of the GO/G-sheets in the NBR matrix, and
their interactions (physical and chemical), may influence the overall mechanical and thermal degradation properties of the 
related composites. 
SEM/EDS analysis of NBR and NBR-GO/G composites 
The SEM images of representative compounds; NBR, G 1 and GO 1 are shown in Fig. 6 a, Fig. 6 b and Fig. 6 c respectively. It  
is usually difficult to see nano-sized particles such as carbon nanotubes and graphene sheets in rubber matrix, as they often
embed themselves deeply in the matrix. Techniques was adopted by Nah et al. [ 75 , 76 ] by imposing forces on the composites
that leads to migration of these nanoparticles from the rubber matrix to the observing surfaces. Although, no such stress 
was used in this present study, however when carefully observed, wrinkled-like GO/G sheets covered with NBR molecules 
and homogeneously distributed within the matrix, are seen at the observing surfaces of the composites. The pure matrix 
( Fig. 6 a) did not show such observation; instead, cryogenically induced surface irregularities can be seen. 
Wrinkled G-sheets covered with silicone rubber molecules was recently also reported by Wang et al. [35] . Such represen-
tative corrugated/wrinkling surface morphologies exhibited by GO/G-sheets are widely reported to be useful in mechanical 
interlocking of the matrix, leading to transfer of load at the interface of GO/G-matrices. This results in enhanced mechanical 
properties for the composites compared to the pure matrix [ 62 , 77 , 78 ]. 6 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
Fig. 4. Curing properties of NBR and NBR-GO/G composites; (a); scorch time (ts2), optimum cure time (t90) (b) effect of GO/G content versus CRI (min −1), 
(c) viscosity index (ML) and (d) crosslinking density (MH) and mechanical strength index ( M). 
Fig. 5. Illustration of the interactions between NBR rubber chain, the GO or G-sheets, sulfur curative and the oxygen functionalities. 
7
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
Fig. 6. SEM images of (a)NBR (b) NBR-G1 and (c)NBR-GO1. And the EDS analysis of (d) NBR (d) G1 and (c) GO1. 
Fig. 7. TEM image of NBR loaded with 1 phr of (a) GO1 and (b) G1 sheets. 
 
 
 
 
 
 
 
 
Earlier, FT-IR technique was used to examine the chemical functionalities of uncured and cured NBR-GO and NBR-G, in- 
cluding their blends with ethylene-propylene-diene monomer rubber (EPDM) [ 32 , 60 ]. Currently, EDS technique is adopted to 
qualitatively distinguish the prominent elements in NBR, NBR-GO and NBR-G compounds. The EDS of representative samples 
of NBR, G 1 and GO 1 are respectively presented in Fig. 6 d, Fig. 6 e and Fig. 6 f. The prominent peaks coming from the elements  
oxygen (O), carbon (C) nitrogen (N) were used to identify the compounds. The order of reducing oxygen content is given by
GO 1 > G  1 > NBR, owing to numerous oxygen functionalities on the GO/G sheets. The nitrogen content increased by GO  1 > 
G 1 > NBR; this trend was due to the presence of nitrile functions (—C≡ N) in NBR [ 79 , 80 ]. That of the composites was found 
to be low, ≡ probably due to reactions of —C N groups with GO/G sheets. The reduction of GO into G by using hydrazine
(N 2H 4) and NH 4OH [49] might be the reason for the high content of nitrogen content in G 1 than GO 1. These elements may     
come from groups that could play roles in crosslinking reactions and influence filler-polymer interactions and the overall 
thermal and physico-mechanical properties of the resulting compounds. 
TEM analysis of NBR, NBR-GO/G composites 
The TEM images of the NBR filled with 1phr of GO and G are shown in Fig. 7 a and Fig. 7 b respectively. Clearly, the
GO/G-sheets seem to show homogeneous dispersions within the NBR matrix, indicating the effectiveness of solution mixing 
as a technique for reinforcing rubber matrices containing GO or G-sheets as summarized in the review reported Mensah 
et al. [26] . The sheets seem to exhibit coiling and corrugating nature coated with the rubber molecules [ 26 , 32 , 42 ]. Similar
to those earlier observed in the SEM analysis, this effect improves the confinement of adjacent rubber chains for effective 
stress deflection at the interface [ 26 , 32 , 42 ]. 8 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
Fig. 8. Reinforcement and memory recovery ability of NBR-GO/G composites measured by (a) crosslinking density Nc(molcm −3) and (b) compression set 
CS (%). 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Crosslinking density and compression set 
The effect of loading of GO and G-sheets on the swelling ratio (Q r) and the chemical crosslinking densities N c(molcm
−3 
 )
  
of NBR matrix is shown in Fig. 8 a The Q r for NBR matrix was high, however, incorporating the fillers (GO/G-sheets) into NBR 
matrix resulted in decline of the Q r properties. This was attributed to the reduction in molecular weight between crosslinks,  
which caused the network’s free volume and solvent permeability to significantly decrease [ 54 , 69 , 81 ]. The low Q r values 
for the composite may be ascribed to factors like; evenly distributions of the GO/G-sheets, their improved interactions with 
the NBR matrix (NBR −GO/G −S x−NBR and NBR −GO/G −NBR) and interactions among themselves; filler-filler interactions  
(GO −GO, GO −S x−S −GO, −3  G −G or G −S x−S −G) [ 26 , 32 ]. It can be suggested that; while the increase in N c(molcm ) for the   
G-composites may be controlled by mere dispersions or increased amount of G −G or G −S x−G bonds in NBR, that of the 
GO-sheets may mainly be due to desired dispersions as well as the strong interactions of GO-sheets with the NBR matrix,
owing to the numerous active oxygenated moieties possessed by GO-sheets [ 26 , 49 , 60 ]. As a result, the low Q r confirms the 
successful dispersion of the GO/G-sheets within the NBR matrix, which has the potential to improve the various physico- 
mechanical properties of the composites, as compared to the virgin matrix. 
Also, the compression set CS (%) properties of the representative samples of NBR, GO 0.1, GO 1, G 0.1 and G 1 performed    
at temperatures of 25-200 °C are shown in Fig. 8 b. The CS (%) values increased as filler content and temperature were in-
creased respectively. In general, an increase in CS (%) indicates the elastomer/composite material’s ability to recover memory 
that has been lost or deteriorated [82] . When compared to the gum, the composites have a lower CS (%), signifying a higher
percentage increase in memory retainable behavior. The increased reinforcing effect of GO/G-sheets in NBR (physical pres- 
ence, enhanced dispersions and strong bond with the matrix) may be responsible for the lower values of CS (%) behavior
observed for the composites [ 26 , 50 ] in relation to the gum. These interactions, tighten the structures of the composites,
disallowing the recovery of the bulk structure, after prolong thermal deformation. By comparison, the G-composites slightly 
showed higher CS (%) properties than the GO-composites counterpart, which is in accordance with the network density, 
N c(molcm
−3 
 ). The CS (%) properties at room temperature of the present compounds ( ∼1.7-1.82 %) are comparable with that
 
of NBR reinforced with (0-50 phr) silanized silica reported by Senthilvel et al. [82] and have outperformed that of NR-carbon
black, NR-GO and NR-carbon nanotubes, whose CS (%) values were reported to be ∼3.5-4.6 %, by Zang et al. [83] . However,
it must be noted that, at this high temperature conditions (10 0-20 0 °C) of sets, thermal degradation and recombination of
crosslinks may be possible [ 54 , 69 ]. 
Thermal degradation of NBR-GO/G in nitrogen medium 
The weight residue, W r(%) as a function of temperature for NBR loaded at different concentrations (0.1-1 phr) of GO and 
G decomposed in nitrogen medium are presented in Fig. 9 ( a - c ) with magnified graphs inserted in each plot for clarity.
The effect of GO or G-sheets loading on the W r(%) of the compounds is also compared in Fig. 9 d. It is generally observed 
that incorporation of the GO/G-sheets into NBR matrix delayed thermal decomposition of the NBR matrix in the nitrogen 
medium, which is very obvious at higher loading of the fillers. For example, at 0.1 phr, GO 0.1 and G 0.1 increased the W r(%) of   
NBR more than 15 and 18% respectively, while the effect shot up to 29 and 63 % for the GO 1 and G 1 composites respectively.  
Furthermore, the maximum temperature of degradation, T max ( °C) of the compositions at different GO/G loading is shown  
in Fig. 10 (a-d) while the effects of GO/G-sheets loading on T max ( °C) are compared in Fig. 10 d. The T max ( °C) for the com-  
posites are generally higher than that of the pure matrix, at all filler loading levels. The combined effect of the physical
presence of the GO/G-sheets, their enhanced dispersions and particularly their strong interactions with the NBR matrix, by 
creating numerous tighter networks (NBR—S x-G—S—NBR, NBR—S x—GO—S—NBR and O—H
σ+ 
  —N σ− —C—) may be the main 
  9 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
Fig. 9. TGA curves depicting the effects of GO/G-sheets loading (0.1-1 phr of GO/G) on thermal degradation of NBR in nitrogen medium (a, b and c) and 
(d) shows the effect of GO/G-sheets loading on the weight residues, Wr(%) of NBR. 
 
 
 
 
 
 
 
 
 
reasons for the thermal degradation resistance of the composites, measured by W r(%). As a result, pyrolysis products in 
GO/G-composites were delayed, causing further degradation of the primary matrix. Notably, the NBR-G composites outper- 
formed NBR-GO composites in terms of W r(%), even though NBR-GO showed higher T max ( °C) characteristics than NBR-G,   
particularly at lower loading levels (0.1 ∼0.5 phr). 
The oxidation of graphite leads to wrinkled/corrugated GO sheets with reduction of the π- π interactions. Chemical re- 
duction of GO with hydrazine in the presence of ammonia hydroxide, restores the sheet-like structures and the π- π inter- 
actions [ 26 , 49 , 50 ]. The restored structure of G, the π- π interaction and the phenyl groups together enhanced the thermal
stability of the NBR matrix [ 26 , 46 ] compared to the highly distorted GO sheets. According to Chu et al. [65] , a more wrin-
kled graphene sheets will exhibit lower thermal conductivity, since the wavy nature of the sheets significantly affects the 
intrinsic characteristics like the aspect ratio of the sheets. Thus, G-sheets may exhibit higher thermal conductivity with cor- 
responding high thermal degradation stability compared to GO-sheets [ 71 , 84 , 85 ] when blended with NBR matrix. This may
be a contributing factor for the high W r(%) observed for NBR-G sheets. The higher thermal conductivity behavior of the 
G-sheets, might have resulted in the reduction of the photon scattering or acoustic impedance mismatch regions at the in- 
terface between NBR and G-sheets [41] . On the other hand, NBR-GO compounds recorded higher T max ( °C) because of strong 
bonds; NBR −S x−GO −S −NBR or O σ+ σ− −H —N −C − that needed to be broken in the course of the thermal process before 
the decompositions process comes to completion. The thermal breakdown of the oxygen moieties on GO into functionalities 
might have increased the pyrolysis of the NBR leading to high weight loss (%) of the NBR-GO. At 1 phr, T max ( °C) for GO  1 
seems to be decreasing; this may be due to agglomeration tendency of GO sheets within NBR, similar to what was observed
earlier by Mensah et al.[ 32 , 36 , 50 ]. In nitrogen medium, the thermal degradation resistances measured by T max and W r(%)  
for the current compositions showed significant improvement compared to those earlier reported for rubber reinforced with 
higher content, functionalized or formation of hybrid system with GDS, as compared in Table 2 with their remarks. 10 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
Fig. 10. DTG curves of NBR, filled different mounts of GO/G-sheets in nitrogen medium; (a) NBR, filled with 0.1 phr of GO/G (b), NBR filled with 0.5 phr 
of GO/G-sheets, (c) 1 phr filled with GO/G-sheets and (d) effect of GO/G-sheets on Tmax ( °C) for the various compositions. 
Table 1 
Compositional formulation of NBR, GO and G compounds (unit phr). 
Code NBR ZnO CZ SA TMTD S GO/G 
NBR 100 5 0.5 1.5 0.25 2 0 
GO 0.1 100 5 0.5 1.5 0.25 2 0.1  
GO 0.5 100 5 0.5 1.5 0.25 2 0.5  
GO 1 100 5 0.5 1.5 0.25 2 1  
G 0.1 100 5 0.5 1.5 0.25 2 0.1  
G 0.5 100 5 0.5 1.5 0.25 2 0.5  
G 1 100 5 0.5 1.5 0.25 2 1  
phr: parts per hundred of rubber; CZ, N-cyclohexyl-2- 
benzothiazolysulfenamide; TMTD, tetramethylthiuram disulfide S; sulfur, 
SA; stearic acid. 
 
 
 
 
 
 
 
Thermal degradation of NBR-GO/G in oxygen medium 
The TGA plot for weight residue, W r(%) versus temperature, for the NBR filled with different content (0.1 ∼1 phr) of GO 
and G, decomposed in oxidative medium are presented in Fig. 11 ( a & b) with magnified graphs inserted in each plots for
clarity. The effect of GO or G content on the W r(%) are also compared in Fig. 11 c. Regardless of the physical presence of the 
GO or G sheets, the content in the matrix or their interactions with the NBR matrix, it was fascinating to observe that the
virgin NBR exhibited tremendous increase in W r(%) than the composites. For instance, NBR showed ∼89, ∼21 and ∼86 % 
than G 0.1, G 0.5 and G 1 respectively and ∼154, ∼350, ∼92 % higher than the respective GO 0.1, GO 0.5 and GO 1 samples. Parallel      
to the case of Nitrogen medium, the NBR-G composites generally showed better W r(%) than the NBR-GO in the oxygen 
medium, seen in Fig. 11 c. 11 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
Table 2 
Comparing T max ( °C) and weight residue W r(%) of current samples and those reported.   
Composition/code % increase in W r (%) T  max( °C) Remarks  
NBR ∼7.2 ∼469 Current work 
GO 0.1 (0.1 phr GO) ∼8.3/7.2 ( ∼15 % > NBR) ∼468 -  
GO 0.5(0.5 phr GO) ∼8.9/7.2 ( ∼24 % > NBR) ∼469 -  
GO 1 (1 phr GO) ∼10.4/7.2( ∼29 % > NBR) ∼467 -  
G0.1 (0.1 phr G) ∼8.5/7.2( ∼18 ‘% > NBR) ∼463 - 
G 0.5 (0.5 phr G) ∼9.3/7.2( ∼29 % > NBR) ∼465 -  
G 1 (1 phr G) ∼11.8/7.2( ∼64 % > NBR) ∼467 -  
BIIRa  (4wt% GO-IL) - ∼405 2013 [41] 
NBR (1 phr GO)b  ∼9.4/7.8 (21% > NBR) 2014 [46] 
SBR (7 phr G) ∼10/6 (67% > SBR) - 2014 [86] 
XNBR (2 phr GO-HDA)c  ∼6.5/4 (63% > XNBR) - 2017 [42] 
NR (1.1 phr of G) ∼12/8 (50% > NR) ∼460 2020 [25] 
PUR (1.9 phr PEG-MGO)d  ∼1.2/1(20% > PUR) ∼475 2022 [87] 
SBR(1.5 wt% GO)e   ∼5.1/2.2(132% > SBR) ∼321 2022 [88] 
SBR(2.5 wt% GO)f   ∼4.8/2.2(182% > SBR) ∼319 2022 [88] 
SR (1 wt% G-BN)g  ∼22.5/14.5(55% > SR) - 2022 [89] 
a GO functionalized ionic liquid in bromo-isoprene isobutylene rubber (BIIR). 
b NBR: author’s previous work, and 
c,d GO functionalized with hexadecyl amine (HDA), Polyurthned rubber (PUR) rein- 
forced with Polyethylene glycol (PEG, molecular weight 600) functionalized multilayer 
graphene oxide (MGO). 
e,f GO functionalized with elastin collagen (COL), 
g silicone rubber(SR) reinforced with (1:1) ratio of Multilayer graphenes (MG) and 
boron nitride (BN) nanosheets. 
Fig. 11. TGA curves showing the effects of GO/G-sheets loading on thermal degradation of NBR in oxygen medium; (a) NBR filled with 0.5 phr GO/G-sheets 
(b) NBR filled with 1 phr GO/G-sheets and (c) the effect of GO/G-sheets loading on the Wr(%) of NBR. 
 
 
 
 
 
 
 
 
 
The derivative thermographs (DTG) of the compounds decomposed in O 2(g) medium are shown in Fig. 12 (a-d). About  
three major degradations can be observed similar to those recently reported for BIIR by Zang et al. [44] . The first, second
and third stages of degradation include; ∼377-398 °C, ∼451-457.2 °C and ∼572.8-580.5 °C respectively. The initial stage of 
decomposition (shown as small neck on the DTG curves) may be due to burning of very weak bonds/structures in GO/G
sheets. It is interesting to observe that the pure NBR matrix did not show such peaks. However, oxidation and rupture of
side groups in silicone rubber chains was observed at ∼365 °C by Wang et al. [35] , on burning in O 2(g) medium. This is 
an indication of thermal degradation stability of polar NBR than silicone matrix. The pyrolysis or de-polymerization of the 
main NBR matrix occurred during the second stage of decomposition ( ∼451-457.2 °C) where T max ( °C) occurs. Even so, the 
nanocomposites generally exhibited higher T max ( °C) temperature at this decompositions due to the presence of GO/G-sheets  
as barrier fillers and strong filler-NBR bonds [35] . As seen in Fig. 12 d. here the G-sheets showed higher T max ( °C), which 
suggests it contributed to the delay of oxygen entering into the matrix to cause thermal oxidation/pyrolysis in NBR-G than 
the case of the highly wrinkled counterpart (GO-sheets) coated with high content of thermal oxidation accelerators(Oxygen 
groups). The third decomposition stage which appeared at the right-neck of the DTG curve around ∼572.8-580.5 °C may be 
due to combustion of the matrix into ashes, associated with high weight residue W r(%) and low weight loss (%) for the pure 
matrix compared with the nanocomposites. 
The poor thermal degradation stability behavior of the NBR-GO/G nanocomposites in this medium may be due to thermo- 
oxidative decomposition of the backbone of NBR accelerated by the highly oxygenated functionalities (C—O—C, —O—C = O and 
O—H) decorating GO/G sheets [ 26 , 28 ], According to Zang et al. [44] , oligomers are formed during thermal chain scission of
BIIR in the presence of oxygen. A large amount of hydrocarbon gas is generated, associated with a severe weight loss. This
is similar to the case observed for the NBR-GO/G composites of this present study. 12 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
Fig. 12. DTG curves of NBR, filled different mounts of GO/G-sheets in oxygen medium; (a) NBR, filled with 0.1 phr of GO/G (b), NBR filled with 0.5 phr of 
GO/G-sheets, (c) 1 phr filled with GO/G-sheets and (d) effect of GO/G-sheets on Tmax ( °C) for the various compositions. 
 
 
 
 
 
 
 
 
 
 
 
 
 
Initial, final and procedural degradation temperature 
The initial IDT ( °C) and final FDT ( °C) degradation temperatures of NBR, NBR-GO/G compounds during decomposition 
in N 2(g) and O 2(g) media are respectively presented in Fig. 13 a and Fig. 13 b. Also, the integral procedural degradation  
temperatures, IPDT ( °C), which represents the volatile part of the compounds during decomposition in N 2(g) and O  2(g) 
media are also compared in Fig. 13 c and Fig. 13 d respectively. In N 2(g), the G-composites seem to show relatively higher 
IDT( °C) than the remaining compounds. However, all the samples maintained similar levels of FDT ( °C) as seen in Fig. 13 a.
A similar observation was made in the O 2(g) medium, except that FDT( °C) of the compositions was higher than in N 2(g)  
medium. In Fig. 13 c, the nanocomposites showed higher IPDT ( °C) than the pure NBR, owing to the barrier effect provided
by the GO and G-sheets in the matrix which slowed down degradation of the bulk matrix. On other hand, the pure NBR
showed higher IPDT ( °C) than the composites in the O 2(g) medium in Fig. 13 d. These results are consistent with the T max ( °C)  
and the weight residue (%) discussed earlier. Therefore, in the N 2(g) medium the GO/G altered the structure of NBR, thereby 
producing higher amount of char residue (%) which thermally insulated NBR and prevented or delayed the diffusion of 
oxygen and other volatile decomposition products from entering the nanocomposite structure [90] . The higher IPDT ( °C) for
the pure NBR than the composites was as result of the degradation process which was facilitated by the thermal oxidation
promoters (C—O—C, —O—C = O and O—H) associated with GO and G fillers. 
Activation energy of thermal decomposition 
According to Zhang et al. [44] , temperature has an indirect association with molecular chain movement, chain relaxation, 
and decomposition activation energy. To understand the overall thermal degradation behavior of the compounds, an inves- 
tigation of the decomposition kinetics of NBR and NBR-GO/G composites was required. The activation energy E a(KJ/mol)  
for thermal decompositions in both in N 2(g) and O 2(g) media of the various composition was obtained by the plots of ln  
[ln(1- α)−1  ] against Ɵ(T-T max) shown in Fig. 14 a and Fig. 14 b respectively for representative samples (NBR, GO and G ). 1 1 
13 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
Fig. 13. The initial (IDT) and final (FDT) degradation temperatures of compounds in (a) N2(g) medium(b) O2(g) medium. The integral procedural degrada- 
tion temperatures (IPDT) of the compounds in (c) N2(g) medium and (d) O2(g) medium. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The estimated E a(KJ/mol) of the samples are compared in Fig. 14 c and Fig. 14 d respectively for N 2(g) and O 2(g) media. It   
was fascinating to observed that higher E a(KJ/mol) was required for thermal breakdown of the NBR-GO in comparison with  
that of NBR-G composites and the gum in the N 2(g) medium. This was in correspondence with the high T max ( °C) observed  
for NBR-GO composites. In the O 2(g) medium, higher E a(KJ/mol) was required to decompose the main chain of NBR as  
compared to the composites, this matched well with the corresponding W r(%) recorded. Yet in the O 2(g) medium, higher  
E a(KJ/mol) was needed to decompose NBR-GO composites, associated with relatively higher weight loss (%) as compared  
with the NBR-G composites. Generally, E a(KJ/mol) is influenced by nature of reactants and the presence of a catalyst. Herein, 
the tight bonding in NBR-GO: NBR—S x—GO—S—NBR and NBR—O—H
σ+ 
   —N σ− —C—NBR caused by the active oxygen groups 
 
(C—O—C, —O—C = O and O—H) on GO may have raised the E a(KJ/mol) for decomposition, even though the final products led 
to lower W r(%).In addition, further crosslinking reactions have been observed in elastomers like BIIR and polychloroprene  
rubber (CR) during the thermal degradation process, owing to the recombination of the radical fragments produced [41] . 
This phenomenon is likely to further increase the E a(KJ/mol) for decomposing of NBR-GO composites in both N 2(g) and  
O 2(g) media compared to NBR-G composites.  
While thermo-oxidative induced crosslinking density may also be possible in the nitrogen medium ( Fig. 14 c) for the com-
posites, especially for NBR-GO, it was not consistent in the case of O 2(g) medium, as the composites decomposed severely 
with relatively lower E a(KJ/mol) and W r(%) relative to that of the pure matrix. It is interesting to observe that NBR-G ex-  
hibited lower E a(KJ/mol) for decomposition in both N 2(g) and O 2(g) media (obviously at lower filler content: 0.1-0.5 phr G),   
although the final W r(%) in both media were the best. This may be due to the presence of the residual hydrazine (N 2H   4) 
present within the structures of G-sheets which acted as catalyst by lowering the E a(KJ/mol) barrier for the decomposition 
of the G-sheets in the bulk NBR-G composites. This is evident in the N 2 (g) medium ( Fig. 14 c) than in O 2(g) medium ( Fig.  
14 d), despite the lower weight loss (%) observed for the final products. This observation is in accordance with the earlier
work on N H reported by dos Santos et al. [91] which investigated the thermal decomposition of N H using TGA. It was2 4 2 4 
14 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
Fig. 14. The plots of ln [ln(1- α) −1] against Ɵ(T-Tmax) for the NBR, GO1 and G1 in (a) nitrogen medium(b) air medium and (c) effect of GO/G-sheet loading 
on activation energy in nitrogen medium (d) effect of GO/G-sheet loading on activation energy in oxygen medium. 
 
 
 
 
 
 
concluded that N 2H 4 is thermodynamically unstable, which is subject to spontaneous decomposition reactions, even at am-   
bient temperature, and it is more reactive in nitrogen atmosphere than in oxygen one. Hence, the thermal instability nature 
of N 2H 4 traces in G-sheets could have sped up the burning process of NBR-G composites, associated with lower E a(KJ/mol).    
Conclusion 
The preparation of acrylonitrile-butadiene rubber (NBR) reinforced with graphene oxide (GO) and reduced graphene Ox- 
ide (G) nanocomposites were achieved by the combination of solution and open-roll blending techniques. The curing behav- 
ior, dispersions of GO/G-sheets in NBR, crosslinking density and compression sets, CS (%), were investigated. Also, the ther- 
mal degradation behavior of the NBR-GO/G composites was separately investigated in air O 2(g) and nitrogen N 2(g) media at  
800 °C, using Thermal gravimetric Analysis (TGA). Solution mixing technique was very efficient as the NBR-GO/G composites 
exhibited higher network density, rheological strengths (M H and M) and high CS (%) than NBR. Also, the char yield of the 
composites was observed to be high, as its delayed further degradation of the NBR matrix in N 2(g) medium, with lower 
amounts of weight loss (%), higher maximum degradation temperatures (IPDT and T max)/( °C) and higher amounts of acti- 
vation energy E a (KJ/mol) for decomposition, particularly for the NBR-GO composites. This was due to the presence of the  
GO/G-sheets and their strong bond with the NBR matrix. In the O 2(g) medium, severe degradation of NBR matrix occurred, 
irrespective of the content of GO/G-sheets incorporated. Thus, in the O 2(g) medium, insignificant char yield was available  
to protect the backbone of NBR matrix from thermal scission, as degradation was accelerated by the highly oxygenated 
groups (C–O–C, –O–C = O and O–H)) on the GO/G-sheets. The harsh decomposition of the composite was associated with 
large amount of weight loss (%) and relatively lower activation energy, E a (KJ/mol) of decomposition as compared to NBR.  
When compared, NBR-G sheet exhibited higher weight residue, W r (%) compared to NBR-GO composites in all decompo-  
sition media. In the N (g) medium, NBR-GO composites exhibited high T max ( °C) than NBR-G composites, due to the tight 2 
15 
B. Mensah, D.S. Konadu, F. Nsaful et al. Scientific African 19 (2023) e01501 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
structures induced by the oxygenated moieties. The NBR-G on the other hand, showed higher W r (%) than NBR-GO com- 
posites suspected to be due to the high thermal conductivity property of less wrinkled G-sheets, as compared to the highly
wrinkled GO-sheets. In terms of kinetics of decomposition, NBR-GO composites generally slowed down of NBR than NBR-G 
composites. This was suspected to be due to the presence of strong bonds like NBR—S x—GO—S—NBR and NBR—O—H
σ+ 
 —N
 
σ−—C—NBR which raised the E a (KJ/mol) for decomposition. The number of these bonds may be lower in the case of NBR-G, 
due to the lower Oxygen-Carbon ratio of G-sheets as compared to GO-sheets. Therefore, in the use of GDS fillers in rubber
matrix for high-temperature applications, the nature of GDS, the matrix and the environment of use, must be considered in 
the design to achieve optimal results. Finally, these NBR-GO/G composites can be used for high temperature and pressure 
applications including oil and gas seals, gaskets materials and rubber products for oil and gas drilling hoses after careful 
optimization. 
Data availability statement 
The data used to support the findings of this study are available from the corresponding author upon request. 
Funding statement 
There was no funding for this research work (self-funding) 
Declaration of Competing Interest 
The authors declare no competing financial interest. 
Acknowledgement 
We acknowledge the support from Professor Changwoon Nah (Intelligent Polymer Nano-materials Lab) of Polymer Nano- 
science and Technology Department, Jeonbuk National University (South Korea), for allowing us to use their facility to carry 
out this study. We also acknowledge the University of Ghana – Carnegie Next Generation of African Academics (UG-Carnegie 
NGAA) Project and the Office of Research Innovation and Development (ORID) at the University of Ghana for their guidance 
towards the completion of the manuscript. 
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