# Fire Behavior of Wood-Glass and Jute-Glass Hybrid Laminates Manufactured by Vacuum Infusion
## 3 Results and Discussion  
The first analysis reported is the cone calorimetry test under a heat flow of 35 kW/m\({}^{2}\) in a horizontal position. The main data obtained from this analysis are reported in Table 1 and then discussed individually. Figure 1: Representation of the VIP for manufacturing the laminates and their different stacking sequences. The times to ignition (TTIs) of the different samples are reported in the first column of Table 1. The TTI is the time required to start burning due to the radiation of heat onto a sample surface in the presence of a spark. The lower the TTI, the more flammable is the material [20]. Considering the TTI necessary for the neat resin used for infusion to ignite (58 \(\pm\) 1 s), this time was greatly diminished for the J5 sample (45 \(\pm\) 1 s) and only slightly so for the WGWGW sample (53 \(\pm\) 3 s). On the other hand, the TTI was postponed for the samples GJGJG (64 \(\pm\) 3 s) and G5 (55 \(\pm\) 15 s). These observations can be attributed to the presence of lignocellulosic material on the face of the WGWGW and J5 laminates. Components like cellulose and hemicellulose in these materials significantly increase their flammability [21]. Conversely, laminates containing glass exhibit longer burn times, particularly on their faces, due to the inorganic nature of glass. Composed of 70-75% silica (SiO\({}_{2}\)), sodium carbonate, and calcium carbonate, glass offers greater resistance to fire exposure [12]. The similarity between the reference polyester and G5 can be explained by the high permeability of glass mats during infusion, which can facilitate the flow of resin through fiberglass mats. Thermal conductivity can also contribute to the first stages of heating and decomposing of the surface of the samples. Wood and jute, for example, have values of conductivity of \(\sim\)0.1 to \(\sim\)0.2 W/(m-K) [22], i.e., higher thermal conductivity compared to glass but similar to the infusion resin. Thermal properties pertain to a material's ability to conduct, store, and dissipate energy. Lower thermal conductivity values accelerate carbonization and temperature accumulation on the surface, leading to quicker pyrolysis and carbonization of the material [12; 23]. This may be an explanation for the variability of samples with more insulating material on the surface such as G5. Parameters such as HRR, pHRR, and THR are important to determine, as they give a general indication of the size of the fire and how quickly it spreads [20; 24]. The speed with which thermal energy is generated by the combustion of a material is important, especially for structural composites, as it indicates its potential fire risk and combustibility, since materials that release smoke and toxic gases relatively quickly are more dangerous than those that do so more slowly [17]. Figure 2A shows the results obtained in relation to the heat release rate (HRR), while Figure 2B refers to the statistical difference according to the confidence interval. Differences can be seen in the time taken for the different laminates to combust, as well as the pure resin. The polyester resin, used for the matrix of the composites, showed the highest HRR peak value (971 \(\pm\) 103 kW/m\({}^{2}\)), which is related to its chemical composition, which contains a considerable amount (35-40%) of styrene in this particular case, as well as highly volatile ester groups [25]. Combustion lasts a long time, with a progressive increase of the HRR in the first stage and a long combustion of the charred part in the final part of the test, which brings the duration of the flaming phase to over 300 s.  
The G5 sample presents an extremely reduced HRR trend compared to the polyester resin. Indeed, the peak was reduced to 322 \(\pm\) 6 kW/m\({}^{2}\). This fact is certainly due to the glass part, which, not being combustible, limits the release of energy during the combustion of the specimen.