Synergistic Effect of Cerium Oxide for Improving the Fire-Retardant, Mechanical and Ultraviolet-Blocking Properties of EVA/Magnesium Hydroxide Composites

Rare earth oxide particles have received important attention in recent years, and due to the wide diversity of promising applications, the need for this kind of material is predicted to expand as the requirements to use the current resources become more demanding. In this work, cerium oxide (CeO2) was introduced into ethylene-vinyl acetate (EVA)/magnesium hydroxide (MDH) composites for enhancing the flame retardancy, mechanical properties and anti-ultraviolet aging performance. The target EVA/MDH/CeO2 composites were prepared by extrusion and injection molding, and the effects of the addition of the CeO2 were explored by thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), limiting oxygen index (LOI), UL-94, cone calorimetry test, and anti-ultraviolet aging test. Typically, the incorporation of the CeO2 allows a significant increase of the elongation at break and Young’s modulus compared with EVA/MDH by 52.25% and 6.85%, respectively. The pHRR remarkably decreased from 490.6 kW/m2 for EVA/MDH to 354.4 kW/m2 for EVA/MDH/CeO2 composite. It was found that the CeO2 presents excellent synergism with MDH in the composites for the anti-UV properties in terms of mechanical properties preservation. Notably, the combination of CeO2 with MDH is a novel and simple method to improve the filler–polymer interaction and dispersion, which resulted in the improvement of the mechanical properties, flame retardancy and the anti-ultraviolet aging performance of the composites.


Introduction
Ethylene-vinyl acetate copolymers are widely used in the industrial field, due to their physical and chemical properties. The EVA thermoplastics containing different vinyl acetate contents can be selected in different areas such as transport, electrical, building and electronics, where the flexibility and processing characteristics of these materials are extensively applied to produce hot-melt adhesive, flexible pipes, battery adhesive film or toys, and especially in the cable industry as an excellent insulating material with good physical and mechanical properties [1][2][3]. The typical disadvantage of these polymers is their high flammability; owing to their chemical structure and composition, they can burn easily, and this issue is a major restriction for their application. The most effective way to overcome this drawback is to add flame retardants to the EVA, and recently much

Mixing of Magnesium Hydroxide with CeO 2
To obtain the modified magnesium hydroxide powder, first, 1000 g of magnesium hydroxide were dried at 110 • C for 6 h to eliminate absorbed water, then the MDH and the cerium oxide powders were added into a high-speed mixer (SHR-10A, Zhangjiagang, China). The temperature and stirring rate of the mixer were set to 100 • C and 2800 rpm. When the set-up temperature was reached, the mixing was kept continuously for 10 min.

Processing of the EVA Composites
All the EVA composites were processed under the same conditions, by hot-melt extrusion of the modified filler into the polymer matrix using a twin screw extruder (Brabender KETSE 20/40) to make the composite polymer granules at 180 • C. In this case the polymer extrusion was made using a 55 wt.% of fillers. The samples for the fire tests and mechanical properties test were obtained by using an injection machine (Arburg Allrounder). The formulations of the samples are given in Table 1. Note: MDH is magnesium hydroxide; CeO 2 is cerium oxide. EM is magnesium hydroxide-filled EVA; EMC is magnesium hydroxide/cerium oxide-filled EVA.

Characterizations
Thermogravimetric analysis (TGA) was performed with a TA thermogravimetric analyzer (Q50, New Castle, PA, USA) from 0 to 800 • C, with a heating rate of 10 • C/min in nitrogen atmosphere. Particle size analysis was performed in a Bettersizer ST, Laser Particle size analyzer (BT-9300 ST). X-ray diffraction (XRD Malvern Panalytical B.V, Almelo, EA, The Netherlands) was carried out on a Panalytical Empyrean diffractometer (Malvern Panalytical B.V, Almelo, EA, The Netherlands) with Cu Kα radiation resource (λ = 0.154 nm) and Cu filter. Limiting oxygen index (LOI) was obtained using an oxygen index meter (FTT, East Grinstead, UK) according to American Society for Testing and Materials (ASTM) D2863-77 standard. The size of the samples was 130 × 6.5 × 3 mm 3 . The vertical burning test was determined with the UL-94 vertical flame chamber (FTT, East Grinstead, UK) according to ASTM D3801 standard. The size of the samples was 130 × 13 × 3 mm 3 . The fire behavior of the samples was determined on a cone calorimeter (FTT, East Grinstead, UK) according to the ISO5660 standard, under a heat flux of 50 kW/m 2 , using a sample size of 100 × 100 × 3 mm 3 . The scanning electron microscope (Helios NanoLab 600i, FEI, Portland, OR, USA) was used for the cross-section and char residue inspections at a voltage of 5.0 kV and 0.69 nA of current. The samples were coated with a conductive layer of gold before SEM observation, and the fractured surface samples were immersed in liquid nitrogen before the gold sputtering.
Tensile testing was performed on a universal electromechanical testing machine (IN-STRON 3384, Norwood, MA, USA) according to ASTM D 638 standard at a test speed of 50 mm/min, and with a load cell of 2000 N. UV radiation was performed in a Dycometal cck-125 climatic chamber irradiance at 40 • C and 35% RH for 0, 24, 48, and 72 h, respectively. The optical microscope Olympus BX51 was used for the surface morphology inspection of the samples after the UV exposure.

TGA and Particle Size of the Fillers
The TGA test was performed for the pure MDH, CeO 2 and for the modified MDH fillers with 3 wt.% and 5 wt.% of CeO 2 ; the obtained results are presented in Table 2 and the corresponding curves were plotted in Figure 1a,b. There was no decomposition observed for the CeO 2 until 800 • C in the TGA test, while the pure MDH showed an initial decomposition temperature of 312.4 • C with a yield of decomposition products of 68.4% at 700 • C, corresponding to the formation of stable MgO [23,24]. After the addition of the CeO 2 , the initial decomposition temperature of the flame-retardant system was increased until 317.5 • C and 324.3 • C for the fillers with a CeO 2 content of 3 wt.% and 5 wt.%, respectively, and the charring capacity was also improved by promoting the formation of a more continuous and more compact barrier layer, obtaining an increase until 71.9% in the residue. Therefore, a suitable amount of CeO 2 can provide higher thermal stability and char-forming behavior to the MDH. This decomposition behavior is in agreement with the TGA results discussed elsewhere [9]. The particle size analysis was performed to obtain the standard dimensions of the flame-retardant fillers; the results are revealed in Table 3; the corresponding curves were plotted in Figure 1c. The additive dispersion through the EVA polymer matrix is a fundamental property for this research work, due to the existence of a high proportion of inorganic particles. The results indicate that the pure MDH has a standard size of 0.98 µm, while the CeO 2 was sized at 0.82 µm; the influence of the rare earth on the MDH flame retardant indicates that for the fillers containing 3 wt.% of the CeO 2 the particle size obtained was of 0.96 µm, and for the fillers containing 5 wt.% of CeO 2 there was a 0.94 µm particle size obtained (Figure 1d). The particle size analysis was performed to obtain the standard dimensions o flame-retardant fillers; the results are revealed in Table 3; the corresponding curves plotted in Figure 1c. The additive dispersion through the EVA polymer matrix is a fu mental property for this research work, due to the existence of a high proportion of ganic particles. The results indicate that the pure MDH has a standard size of 0.98 while the CeO2 was sized at 0.82 m; the influence of the rare earth on the MDH f retardant indicates that for the fillers containing 3 wt.% of the CeO2 the particle siz tained was of 0.96 m, and for the fillers containing 5 wt.% of CeO2 there was a 0.94 particle size obtained ( Figure 1d). In order to compare the influence of CeO2 on the comprehensive properti EVA/MDH composites, we designed four samples as shown in Table 1. The compo are obtained by twin-screw extrusion, and then all test specimens required to be t are obtained by injection molding. The preparation process is shown in Figure 2a SEM cross-section was performed to study the additive dispersion within the pol matrix, and the evaluation indicates that the pure EVA sample has a smooth and co uous fracture surface (Figure 2b). After the 55 wt. % of pure MDH was added int EVA, the fracture surface of the composite shows the good dispersion of the filler thr the EVA matrix ( Figure 2c). While due to the existence of a high proportion of inor  In order to compare the influence of CeO 2 on the comprehensive properties of EVA/MDH composites, we designed four samples as shown in Table 1. The composites are obtained by twin-screw extrusion, and then all test specimens required to be tested are obtained by injection molding. The preparation process is shown in Figure 2a. The SEM cross-section was performed to study the additive dispersion within the polymer matrix, and the evaluation indicates that the pure EVA sample has a smooth and continuous fracture surface (Figure 2b). After the 55 wt.% of pure MDH was added into the EVA, the fracture surface of the composite shows the good dispersion of the filler through the EVA matrix ( Figure 2c). While due to the existence of a high proportion of inorganic particles, samples EM, EMC3 and EMC5 all show irregular and rough cross-section morphology. In particular, we found a significant crack in Figure 2c, which will lead to the low mechanical properties of the sample to a certain extent. The further addition of the 3 wt.% and 5 wt.% CeO 2 with a particle size of 0.82 µm can help to form a more uniform surface (Figure 2d,e) with smaller gaps between the fillers and the polymer matrix, and finally improve the performance of the mechanical and flame-retardant properties of the composites, which will be provided in Section 3.4.
particles, samples EM, EMC3 and EMC5 all show irregular and rough cross-section morphology. In particular, we found a significant crack in Figure 2c, which will lead to the low mechanical properties of the sample to a certain extent. The further addition of the 3 wt.% and 5 wt.% CeO2 with a particle size of 0.82 μm can help to form a more uniform surface (Figure 2d,e) with smaller gaps between the fillers and the polymer matrix, and finally improve the performance of the mechanical and flame-retardant properties of the composites, which will be provided in Section 3.4.

X-ray Diffraction (XRD)
XRD analysis was performed to reveal the diffraction peaks of the pure and modified EVA composites; the XRD curves are plotted in Figure 3. The pure EVA sample has two diffraction peaks at 21.2° and 23.5°, corresponding to the (110) and (002) atomic crystal planes of EVA. The sample containing EVA and the unmodified MDH also has peaks at 18.7°, 38.1°, 50.9°, 58.8°, 62.2° and 68.3°, which fit exactly into the diffraction of the MDH crystals at (001), (101), (102), (110), (111), and (103), in accordance with the literature. [25] In this case, the samples containing cerium oxide exhibited additional peaks at 28.80°, 33.10°, 48.10° and 56.80° that correspond to the (111), (200), (220) and (311) crystal planes of the rare earth oxide [26,27].    phology. In particular, we found a significant crack in Figure 2c, which will lead to the low mechanical properties of the sample to a certain extent. The further addition of the 3 wt.% and 5 wt.% CeO2 with a particle size of 0.82 μm can help to form a more uniform surface (Figure 2d,e) with smaller gaps between the fillers and the polymer matrix, and finally improve the performance of the mechanical and flame-retardant properties of the composites, which will be provided in Section 3.4.  (103), in accordance with the literature. [25] In this case, the samples containing cerium oxide exhibited additional peaks at 28.80°, 33.10°, 48.10° and 56.80° that correspond to the (111), (200), (220) and (311) crystal planes of the rare earth oxide [26,27].     The DSC results are shown in Table 4 and the corresponding curves are presented in Figure 4a. All the samples presented the traditional endothermic and exothermic peaks and the thermal properties were recorded from the second heating run. The glass transition of −28.2 • C was observed for pure EVA with a melting temperature of 75.1 • C and a melting enthalpy of 23.2 J/g related to the slightly crystalline phase of the EVA, as previously reported in the literature [28]. No significant changes were observed in the glass transition and melting temperatures after the addition of the pure MDH and modified MDH with CeO 2 filler, however, a decrease on the melting enthalpy was obtained for the EVA composites; the pure MDH composites showed a melting enthalpy of 13.9 J/g and the samples containing cerium oxide have a lower enthalpy of 11.2 and 11.1 J/g, indicating that the addition of the rare earth is leading to the absorption of lower amounts of heat during the melting cycle of the composites. We can understand that the possible crystallization of EVA is inhibited for pure MDH modified composites due to the introduction of impurities in MDH. Therefore, the enthalpy decreased significantly. With the introduction of CeO 2 , it shows that the good dispersion of CeO 2 can inhibit EVA crystallization to a greater extent.

TGA Analysis of the EVA Composites
The thermal stability of the EVA composites was measured by the TGA in a nitrogen atmosphere, the summarized data is presented in Table 5, and the related curves are plotted in Figure 4b. The EVA composites exhibited a two-step decomposition process. The first step involves the dehydration of MDH and the loss of acetic acid in EVA at the range of 300-400 • C [23], whereas the second degradation step at the temperature range of 400-550 • C is due to the degradation of ethylene-based chains and to the volatilization of residual polymer [29]. Compared with the pure MDH samples, there is a small shift observed in the T-5% for the samples with cerium oxide; it can be seen that the T-5% of the EM was 327.4 • C, while the EMC3 and EMC5 samples have a lower T-5% of 324.4 • C and 319.1 • C, respectively. In contrast, the char residue at 700 • C was significantly improved;  In addition, as shown in Figure 4c,d, the decomposition in the first stage is advanced, and the maximum thermal decomposition rate in the second stage decreased (Figure 4d). All these show that the introduction of CeO 2 can significantly change the thermal decomposition path of the composite, so it has more significant char-forming ability. Specifically, as listed in Figure 4b and Table 5, when CeO 2 is present, it has significantly higher char residue than that of the EM sample.

Fire Safety Performance
The effect of MDH, MDH/cerium oxide on the flammability of EVA was studied by limiting oxygen index (LOI) and UL-94 vertical burning test ( Table 6). The LOI value of pure EVA was only 18.2% and it failed to pass UL-94 rating. When 55 wt.% MDH was added, the LOI value increased to 40.9% and the composites passed the UL-94 V-0 rating. After 3 wt.% of the CeO 2 was added to the EVA system, the LOI value slightly decreased to 38.5% while keeping the UL-94 V-0 rating. After the addition of 5 wt.% of the CeO 2 the LOI result was 39.9% and the UL-94 rating was V-0. The addition of the CeO 2 caused a slight decrease in the LOI value; however, the CeO 2 functionalized flame-retardant composites both presented high efficiency and at this loading of fillers the composites were still able to reach the V-0 rating according to the UL-94 standard. To investigate the flame-retardant effect of the modified MDH on the EVA composites, cone calorimeter tests were performed at an external heat flux of 50 kW/m 2 . The combustion data, including heat release rate (HRR), total heat release (THR), total smoke production (TSP), and residue, are summarized in Table 7, and the curves of HRR, TSP and char residue versus time for the EVA composites are presented in Figure 5.  The interesting synergy between the rare earth filler and the MDH has also produced the smoke suppression effect in the EVA system; the composites containing the modified fillers have reduced the smoke production of the EVA composites from 8.6 m 2 until 7.9 m 2 ( Figure 5b). As shown in Figure 5c, we can find that with the addition of CeO2, the char residue increased, which is in good agreement with the results of TGA tests. Furthermore, From Figure 5a, it can be seen that the heat release rate (HRR) curve of pure EVA has a sharp peak, which indicates the furious burning and heat release. This result is caused by the free combustion of hydrocarbon chains [4]. When the 55 wt.% of MDH was introduced, peak heat release rate (pHRR) values of the resulting composites were considerably reduced. The decomposition of the modified MDH can limit the access of oxygen to the internal layer of material, causing a heat dissipation effect known as "heat sink" during the first stage of decomposition; MDH can also release water molecules while the metal oxide barrier is formed [30].
The most interesting effect of the incorporation of the CeO 2 is the decrease of the heat release. In fact, the incorporation of even a relatively low amount (3 wt.%) results in the reduction of the pHRR of about 14% (from 491 kW/m 2 for EM to 425 kW/m 2 for EMC3). Moreover, with the addition of 5 wt.% of the CeO 2 , the pHRR reduction is higher (28%).
The interesting synergy between the rare earth filler and the MDH has also produced the smoke suppression effect in the EVA system; the composites containing the modified fillers have reduced the smoke production of the EVA composites from 8.6 m 2 until 7.9 m 2 ( Figure 5b). As shown in Figure 5c, we can find that with the addition of CeO 2 , the char residue increased, which is in good agreement with the results of TGA tests. Furthermore, the modified EVA composites present significant increased TTI as shown in Figure 5d. Both the HRR and THR, of all of flame-retardant samples containing MDH/CeO 2 , showed an evident decrease during burning (Figure 5e,f). All the above indicate that the MDH/CeO 2 fillers can improve the fire safety of the composites, and the samples with incorporation of CeO 2 performed much better than those with MDH only.
The fundamental role of CeO 2 in the flame-retardancy enhancements is assigned to the yielding of a larger amount of solid inorganic residues that serve as a barrier to heat and mass transfer between the pyrolysis zone and the underlying polymer [31]. Typically, as shown in Figure 6, the char residue of the composite increased significantly. In addition, we can clearly see that the introduction of CeO 2 makes the residual char denser and continuous. Neither EMC3 nor EMC5 have significant micro-cracks compared to sample EM (Figure 6c). Thus, a suitable amount of CeO 2 plays a critical role in the flame-retardancy and char-forming behavior of EVA/MDH and promotes the formation of more compact char structures in the EVA/MDH composites, which is in good agreement with the literature elsewhere [9].
in gas phase [32][33][34][35]. As shown in Table 7, average EHC (AEHC) was decreased from 35.9 MJ/kg for EVA to 28.6 MJ/kg for EM, and further decreased to 26.3 and 21.8 MJ/kg with the addition of 3 and 5 wt. % of cerium oxide, respectively; the enhanced EHC performance was attributed to the increase of concentration of noncombustible compounds in the gas phase and the higher char residue formed by the inorganic filler's action. As a result, the heat and mass transfer between the combustion phases was delayed by the imparted flame retardancy. By using these enhanced composites with lower heat release and smoke production and with enhanced charring ability, it is possible to increase the fire safety in the final appliances.

Mechanical Properties
In the context of the inorganic filler composites, mechanical properties are inevitably concerned besides their flammable characteristics. The high weight fraction of MDH filler additive in polymers can adversely affect some mechanical properties, and often decrease their failure properties [36]. It can be seen from Table 8 that the value of tensile strength decreased from 18.6 to 9.6 MPa when using the MDH to modify the EVA. This reduction in the mechanical properties accounts for the agglomeration of the flame-retardant particles and the interface gaps leading to non-uniform stress distribution in the composites The effective heat of combustion (EHC), defined as the ratio of heat release to mass loss at a certain time during combustion, can exactly reveal the burning degree of volatiles in gas phase [32][33][34][35]. As shown in Table 7, average EHC (AEHC) was decreased from 35.9 MJ/kg for EVA to 28.6 MJ/kg for EM, and further decreased to 26.3 and 21.8 MJ/kg with the addition of 3 and 5 wt.% of cerium oxide, respectively; the enhanced EHC performance was attributed to the increase of concentration of noncombustible compounds in the gas phase and the higher char residue formed by the inorganic filler's action. As a result, the heat and mass transfer between the combustion phases was delayed by the imparted flame retardancy. By using these enhanced composites with lower heat release and smoke production and with enhanced charring ability, it is possible to increase the fire safety in the final appliances.

Mechanical Properties
In the context of the inorganic filler composites, mechanical properties are inevitably concerned besides their flammable characteristics. The high weight fraction of MDH filler additive in polymers can adversely affect some mechanical properties, and often decrease their failure properties [36]. It can be seen from Table 8 that the value of tensile strength decreased from 18.6 to 9.6 MPa when using the MDH to modify the EVA. This reduction in the mechanical properties accounts for the agglomeration of the flame-retardant particles and the interface gaps leading to non-uniform stress distribution in the composites [37]. However, the CeO 2 -containing system shows an improved value of TS (10.1 MPa), and the elongation at break of 202.9%, indicating that the influence of the CeO 2 structure and particle size can lead to a more uniform dispersion due to an enhanced interfacial interaction (Figure 1d,e) [38]. With the same filler mass ratio, good dispersion will contribute to the significant improvement of Young's modulus. In this case, Young's modulus increased significantly from 69 MPa for EM to 76 MPa for EMC3. Its specific tensile curves and the key parameters tendency are all shown in Figure 7. Usually, the tensile strength of the polymeric materials is severely affected when MDH is added as a major flame retardant [39], therefore the ability to reverse this effect by generating an increased tensile strength up to 5% of CeO 2 represents a very high functionality in this type of material, and this is because the CeO 2 promotes the mechanical stability of the material by generating better dispersion and combination with the polymer matrix. of the polymeric materials is severely affected when MDH is added as a major flame retardant [39], therefore the ability to reverse this effect by generating an increased tensile strength up to 5% represents a very high functionality in this type of material, and this is because the CeO2 promotes the mechanical stability of the material by generating better dispersion and combination with the polymer matrix.   CeO 2 , being one of the most chemically active rare earth oxides, is resistant to ultraviolet light [26]. Along with the incorporation of the rare earth into the formulation of the EVA-MDH composites, we expect to additionally increase the performance of this material as a result of the anti-UV functionalities that the CeO 2 has inherently. Figure 8 shows the optical microscope images of the pure EVA and EVA/MDH/CeO 2 composites before and after the UV treatment at different times; for the pure EVA samples, the formation of micro-cracks due to the excessive swelling has led to the displacement of layers in the surface of the polymer after 72 h of UV exposure; the samples containing the pure MDH also showed large cracks (see the red circle area), although the polymer layers were more uniform and the degradation was consistently smaller. In contrast, no significant degradation was observed for the samples containing the CeO 2 after 72 h of UV irradiation, indicating that the CeO 2 can effectively delay the diffusion of the UV radiation. and after the UV treatment at different times; for the pure EVA samples, the formation of micro-cracks due to the excessive swelling has led to the displacement of layers in the surface of the polymer after 72 h of UV exposure; the samples containing the pure MDH also showed large cracks (see the red circle area), although the polymer layers were more uniform and the degradation was consistently smaller. In contrast, no significant degradation was observed for the samples containing the CeO2 after 72 h of UV irradiation, indicating that the CeO2 can effectively delay the diffusion of the UV radiation. Figure 8. Optical microscope images of the pure EVA and its composites' surface morphologies before and after exposure to UV, by different times.

Tensile Test after the UV Exposure
The mechanical test results for the non-exposed and UV-exposed samples are shown in Figure 9. The 72 h of UV exposure had a remarkable deteriorative effect on the mechanical properties of the pure EVA samples, the elongation decreased from 722% until 401% while the tensile strength was also decreased from 18.6 MPa until 8.4 MPa (with a reduction of 54.84%). In the case of the EM samples, a lower decay but significant decrease of the mechanical properties was observed. Namely, the elongation was reduced from 167% until 71.2%, and the tensile strength from 9.6 MPa until 4.9 MPa (with a reduction of Figure 8. Optical microscope images of the pure EVA and its composites' surface morphologies before and after exposure to UV, by different times.

Tensile Test after the UV Exposure
The mechanical test results for the non-exposed and UV-exposed samples are shown in Figure 9. The 72 h of UV exposure had a remarkable deteriorative effect on the mechanical properties of the pure EVA samples, the elongation decreased from 722% until 401% while the tensile strength was also decreased from 18.6 MPa until 8.4 MPa (with a reduction of 54.84%). In the case of the EM samples, a lower decay but significant decrease of the mechanical properties was observed. Namely, the elongation was reduced from 167% until 71.2%, and the tensile strength from 9.6 MPa until 4.9 MPa (with a reduction of 48.96%). As for the EMC3 samples the elongation was reduced from 202% to 94% and the tensile strength slightly decreased from 10.1 MPa to 7.6 MPa (with a reduction of 24.75%). The EMC5 samples showed a more reduced trend, the elongation was reduced slowly from 254% to 192%, and the tensile strength from 9.1 to 7.6 MPa (with a reduction of 16.48%), indicating that the effects of the UV irradiation were significantly decreased with the addition of the CeO 2 . Therefore, it is valuable to note that CeO 2 could be used effectively as the reinforcement filler to improve the UV-aging resistance of EVA-MDH polymer composites by forming physical barriers that can improve the shielding of the polymer matrix against the UV exposure-the mid-term and long-term degradation of EVA during its effective service usually involves the ultraviolet radiation from sunlight [40], and the systematical enhancement of this functional property is a key solution for improving the EVA polymer composites' durability.
addition of the CeO2. Therefore, it is valuable to note that CeO2 could be used effectively as the reinforcement filler to improve the UV-aging resistance of EVA-MDH polymer composites by forming physical barriers that can improve the shielding of the polymer matrix against the UV exposure-the mid-term and long-term degradation of EVA during its effective service usually involves the ultraviolet radiation from sunlight, [40] and the systematical enhancement of this functional property is a key solution for improving the EVA polymer composites' durability.

Conclusions
EVA composites with MDH and CeO2 additives were prepared by hot-melt extrusion and injection molding. The initial flammability tests show the improvement in the LOI values from 18.2% (unmodified EVA) to 40.9% (EM), and after the addition of the rare earth a slight reduction in LOI values was observed-the LOI for EMC3 and EMC5 were 38. 5% and 39.9%, respectively. However, all the modified EVA composites can pass the V-0 rating in the UL-94 vertical burning test. The introduction of the CeO2 has created different improvements in the fire properties of the composites measured in the cone calorimetry-a decrease of 59% in the pHRR was obtained for the EM system, while the EMC3 and EMC5 showed a pHRR reduction of 64% and 70%, respectively, and the smoke production was also decreased from 13.9 m 2 to 7.9 m 2 (EMC5) and the charring capacity of the samples was enhanced up to 40% (EMC5). The improvements obtained in the flame retardancy of the composites can be related to enhanced activity against the fire in both the condensed and gas phases. The cerium oxide system has presented an interesting advantage in terms of mechanical strength and elongation at break; the tensile strength was improved from 9.6 MPa (EM) to 10.1 MPa (EMC) and the elongation at break was also enhanced from 166% to 254%. The obtained results can reveal that by including non-toxic halogen-free flame retardants in the EVA system, it is possible to improve the functional properties of the EVA composites, and in this case the UV-blocking properties of the CeO2 have also led to a higher preservation of the mechanical properties after 72 h of ultraviolet light irradiation. Notably, the multifunctional fillers used in this research work can offer a promising solution in the future developments of high-performance EVA polymer composites.

Conclusions
EVA composites with MDH and CeO 2 additives were prepared by hot-melt extrusion and injection molding. The initial flammability tests show the improvement in the LOI values from 18.2% (unmodified EVA) to 40.9% (EM), and after the addition of the rare earth a slight reduction in LOI values was observed-the LOI for EMC3 and EMC5 were 38. 5% and 39.9%, respectively. However, all the modified EVA composites can pass the V-0 rating in the UL-94 vertical burning test. The introduction of the CeO 2 has created different improvements in the fire properties of the composites measured in the cone calorimetry-a decrease of 59% in the pHRR was obtained for the EM system, while the EMC3 and EMC5 showed a pHRR reduction of 64% and 70%, respectively, and the smoke production was also decreased from 13.9 m 2 to 7.9 m 2 (EMC5) and the charring capacity of the samples was enhanced up to 40% (EMC5). The improvements obtained in the flame retardancy of the composites can be related to enhanced activity against the fire in both the condensed and gas phases. The cerium oxide system has presented an interesting advantage in terms of mechanical strength and elongation at break; the tensile strength was improved from 9.6 MPa (EM) to 10.1 MPa (EMC) and the elongation at break was also enhanced from 166% to 254%. The obtained results can reveal that by including non-toxic halogen-free flame retardants in the EVA system, it is possible to improve the functional properties of the EVA composites, and in this case the UV-blocking properties of the CeO 2 have also led to a higher preservation of the mechanical properties after 72 h of ultraviolet light irradiation. Notably, the multifunctional fillers used in this research work can offer a promising solution in the future developments of high-performance EVA polymer composites.