Vertical Force (VF) Measurements
VF during the compounding was measured to determine the melt-flow properties of COPE, R-COPE, and their composite with Calcite at different concentrations. In all composites, the barrel temperatures and screw rotation speed were kept constant. In this way, the vertical force values of the polymer melt against time at constant temperature and screw rotation speed were recorded in Newton (N) units every 30 seconds. The viscosity value of polymer and polymer composites that changes over time with the effect of temperature and screw revolution in the extruder has been correlated with the VF comparison. The variation of vertical force in COPE, R-COPE, and their composites with calcite were given in Fig. 1. It was seen that virgin and recycled COPE had the lowest melt viscosity VF data were compared with the torque values required for the screw to rotate at the adjusted rpm value. An increase in the melt viscosity values was observed after the COPE polymer was blended with calcite at different rates [23]. Caner et al. observed a similar trend in VF values by addition of different compatibilizers to poly(lactic acid)/ (PCL)4-POSS-(PLA)4 blends [23, 41, 42]. As the calcite concentration increased, an increase was observed in the VF values. The highest viscosity values were observed in the COPE/Calcite30 and R-COPE/Calcite30 composites having the highest amount of calcite. It has been determined that the melt viscosities decreased with the effect of temperature and screw over time. It was seen that VF values decreased over time as the amount of calcite decreased in all polymer composites [41]. This shows that the melt viscosity decreases with time and the fluidity of polymer composites increases with time.
Mechanical Properties
The mechanical results of the COPE (virgin) and R-COPE (recycled) composites containing calcite are shown in Figs. 2–6. For comparison, the tensile results for the virgin COPE and R-COPE composites are shown in Fig. 2. When 30%wt. calcite was added to the COPE matrix, the tensile strength value decreased from 36.16 MPa to 32.66 MPa. The lowest tensile strength value (MPa) was observed in the COPE mixture containing 30%wt. calcite. The reason for this is that the tensile strength values increased until a certain calcite reinforcement, the material approached a ductile structure to a brittle structure from 20%wt. calcite reinforcement, and serious decreases were detected in the breaking strength values. Along with the homogeneous distribution in the matrix, the highest tensile strength value was determined for the COPE/Calcite20 composite. If we draw a conclusion by comparing the tensile strengths, up to 20% calcite reinforcement, the tensile strength values increased compared to the unfilled products, and decreases occurred in the 30% filled products. Additionally, no significant difference was detected when the tensile strength values of the COPE and R-COPE composites were compared.
The elongation at break (%) of the virgin COPE polymer was determined to be 459.72% in the tensile tests, as shown in Fig. 3. The high elongation at break indicates that the polymer is flexible, soft, and tough. The highest elongation at break (%) value in the COPE/calcite composites was 530.0% for the COPE/Calcite10 composite, and the % elongation values of all polymer composites with up to 20% calcite reinforcement yielded higher % elongation results than their pure state. Elongation decreased with increasing calcite concentration. In all composite mixtures, the elongation at break values of the recycled products was higher than those of the virgin composite products.
The yield strength is the value at which the material passes from the elastic strain region to the plastic strain region. When the load applied below the yield limit value is removed, the polymer returns to its former physical state. When a load above this value is applied, the polymer no longer begins to flow and passes into the plastic deformation zone, as shown in Fig. 4. The values increased with the calcite concentration at the flow boundaries. This shows that the brittleness value of the materials increased as the amount of calcite increased. A transition from a tougher flexible material to a more rigid material occurs. The yield limit of the COPE polymer was determined as 7.44 MPa and this value increased up to 10.07 in the COPE/Calcite30 polymer composite.
According to the impact strength results of the COPE/calcite composites, the impact strength of virgin COPE was the lowest, as shown in Fig. 5. The impact strength values increased in all the polymer blends with the addition of calcite. An increase of 44% was detected in the COPE/Calcite30 composite and an increase of 28.6% in the R-COPE/Calcite30 polymer.
To determine their hardness, materials such as polymers, elastomers, and rubbers were tested using a durometer. The penetration of the tip across the sample was measured. Figure 6 shows the changes in the Shore-D hardness of the COPE and R-COPE composites. The lower the deformation, the higher the hardness of the material. An increase in the Shore-D values of the composite materials was observed with increasing filler concentration. The highest shore value was observed for products with 30%wt calcite.
3.3. Physical Properties of COPE Composites
The density value of the pure COPE polymer was recorded as 1.15 g/cm3 according to the results of the density measurement in Fig. 7. A slight linear increase was observed in all composites with the addition of calcite. It is a COPE/Calcite30 polymer composite containing 30% calcite, with a maximum density value of 1.37 g/cm3 and which was 19.13% higher than that of the virgin and recycled COPE polymers.
3.4. Morphological properties of COPE Composites
Analysis of the phase morphology of the composite system supplies direct information on the mechanical properties of the obtained composites. SEM and EDX were utilized to investigate the morphological properties of the composites. SEM images of COPE, R-COPE, and selected composites (with 30% calcite) were reported in Fig. 8 at different magnification rates (1000x and 10 000x). When the SEM images of COPE and R-COPE were examined, it was seen that the folds seen on the COPE and R-COPE surfaces were an indication of high plastic deformation before breaking. COPE and R-COPE exhibited ductile fracture because of their relatively low glass transition temperatures and high toughness. No cracks were observed in the SEM images due to the ductile fracture feature. Relative increases in the impact strength of COPE were observed when calcite was added, and it was confirmed when the fracture surfaces were examined that it was a more flexible material, and the ductile rupture morphology was dominant. Examining the SEM images of the COPE and R-COPE composite samples showed similar observations that the calcite was homogeneously distributed in the COPE and R-COPE matrix at low feed rates. As the additive content increased, the formation of calcite regions like agglomeration was not observed, but it was observed that the dispersion effect decreased with the increase in the amount of calcite additive. With the good distribution effect, agglomerations were prevented, but due to the weak dispersion effect, the calcite contribution could not show an equal distribution all over the matrix.
The EDX spectrum and the atomic composition of the COPE, COPE/Calcite30, and R-COPE/Calcite30 composites were given in Fig. 9. It is known that there were no traces of Ca atom observed in COPE in Fig. 9 (a). However, the EDX maps of COPE/Calcite30 (Fig. 9(b)) and R-COPE/Calcite30 (Fig. 9(c)) composites represent the presence of Ca atom by yellow dots dispersed in the matrix. The presence of Ca atoms is evidence of the presence of calcite filler used in the study of polymer matrices. By superimposing the red, green, and yellow dots (C, O, Ca), the ratio of these atoms to each other, their positions, and location mapping were revealed. The dispersion of Ca atoms was homogenous, indicating homogenous dispersion of calcite in the composite matrix.
Thermal Analysis of Polymer Composites
The cold crystallization temperature (Tc) and the melting temperature (Tm) of the COPE, R-COPE, and their composites with calcite which were prepared at different concentrations were taken from DSC. The related data which refers to the second heating step summarized in Table 1. DSC thermograms of the COPE, R-COPE, and their composites were given in Fig. 10. The COPE polymer and R-COPE polymer showed a melting temperature of around 149.9°C and 149.53°C, respectively. It was observed that there was a general increase in the Tc and Tm temperatures of COPE and R-COPE polymers depending on the amount of calcite filler addition, indicating that the addition of calcite filler improved the thermal stability of the composites. It can be attributed that the slight increase in Tc activates the calcite filler as a nucleating agent in the matrix and increased the Tc temperature. Compared with COPE and R-COPE composites, it can be seen that the higher the crystallization temperature, the better the nucleating agent effect of calcite in the recycled matrix. Furthermore, virgin COPE exhibited a broad exothermic peak before the main melting peak. This indicated that recrystallization occurred in the hard crystalline region that had sufficient mobility to crystallize during heating screening. In the case of composites, the limited mobility of polymer chains by calcite causes no recrystallization during the heating process [24].
Table 1 DSC results of COPE, R-COPE, and their composites with calcite.
Entry
|
Tc
(oC)a
|
Tm
(oC)b
|
ΔHc
(J/g)c
|
ΔHm
(J/g)d
|
COPE
|
110.1
|
149.9
|
-12.3
|
11.6
|
COPE/Calcite5
|
110.7
|
150.6
|
-11.0
|
12.0
|
COPE/Calcite10
|
111.9
|
150.8
|
-10.9
|
10.7
|
COPE/Calcite15
|
111.2
|
151.6
|
-13.2
|
12.8
|
COPE/Calcite20
|
112.3
|
151.7
|
-9.3
|
7.6
|
COPE/Calcite30
|
114.4
|
152.6
|
-8.4
|
8.4
|
R-COPE
|
123.3
|
149.5
|
-13.3
|
14.9
|
R-COPE/Calcite5
|
127.4
|
151.6
|
-9.2
|
6.8
|
R-COPE/Calcite10
|
128.4
|
151.4
|
-8.5
|
12.3
|
R-COPE/Calcite15
|
125.8
|
150.8
|
-8.7
|
5.9
|
R-COPE/Calcite20
|
130.9
|
152.4
|
-6.9
|
6.1
|
R-COPE/Calcite30
|
132.1
|
154.3
|
-5.5
|
3.7
|
aTc, bTm, cΔHc, and dΔHm denote the cold crystallization, the melting point temperature, enthalpy of crystallization and melting of the polymer and composites in the second heating run of the DSC experiments in turn.
|
TGA thermograms of COPE, R-COPE, and their composites containing calcite were given in Table 2 and Fig. 11. The effect of the addition of calcite at different concentrations on the thermal stability of the polymer matrix was evaluated according to the data obtained by TGA. As can be seen from the TGA curves, it was seen that the use of calcite in all composites did not significantly change the thermal stability of polymer composites. It was observed that the Tonset, T5, and T50 temperatures increased to higher temperatures with the increase of the calcite amount. When we compare COPE and R-COPE matrix composites; an increase of 1.1°C was detected in the Tonset of the R-COPE polymer compared to the COPE polymer. When the T50 temperature, where 50% mass loss was observed in R-COPE/Calcite30 and COPE/Calcite30 polymer composites, where the maximum amount of calcite was fed, an increase of 3.35°C was detected for the R-COPE polymer matrix. It has been observed that char yield was affected by the amount of calcite. It has been determined that the char yield increases significantly with the increase in the amount of calcite in the polymer matrix.
Table 2 TGA results of COPE, R-COPE, and their composites with calcite.
Entry
|
Tonset
(oC)a
|
T5%
(oC)b
|
T50%
(oC)b
|
Tmax
(oC)c
|
Char Yield
(%)d
|
COPE
|
377.2
|
367.7
|
402.0
|
404.3
|
6.6
|
COPE/Calcite10
|
379.4
|
368.9
|
402.5
|
404.2
|
12.8
|
COPE/Calcite20
|
379.8
|
369.8
|
406.2
|
404.2
|
22.7
|
COPE/Calcite30
|
382.0
|
371.9
|
412.1
|
404.1
|
32.3
|
R-COPE
|
378.3
|
368.9
|
401.2
|
404.1
|
6.6
|
R-COPE/Calcite10
|
380.7
|
369.8
|
402.5
|
404.2
|
12.8
|
R-COPE/Calcite20
|
380.7
|
371.4
|
407.9
|
404.3
|
23.7
|
R-COPE/Calcite30
|
382.0
|
371.9
|
415.5
|
404.3
|
33.7
|
aTonset represents the onset decomposition temperature of the films.
bT5% and T50% represents the temperatures of weight loses at 5% and 50% in turn.
cTmax are the temperature that corresponds to the maximum rate of weight loss.
dThe percentage weight remaining at 600°C.
|