Studies On Structure Development Of Poly (Vinyl Chloride)/Flame-Retardant And Smoke-Suppressant System During Thermal Decomposition And Mechanism Of Flame Retardancy And Smoke Suppression

Poly(vinyl chloride) is second in volume only to polyethylene. It has large and broad uses in many industrial applications, especially in building application. However, there is a growing realization that PVC is not a safe material from the point of view of fire hazard due to its release of high levels of smoke and toxic gases (hydrogen chloride, benzene and other aromatic compounds etc) during burning. So flame retardancy and smoke suppression during burning of PVC could have profound consequences as PVC is increasingly used to produce building materials. In this paper, the research works of recent years on flame retardancy and smoke suppression of PVC were reviewed. Based on the major problems, which have not been solved, we proposed our academic dissertation foundation, and put forward the working scheme. By using on-line measurement of conductivity, the effects of each kind of flame-retardant/smoke-suppressant (FRs) on the elimination of HC1 during thermal decomposition of PVC were investigated and the kinetic modes were proposed. TGA, FT-IR, UV, WAXD and ESCA methods were used to detect both gas phase and condensed phase, deriving from decomposition of PVC. Meanwhile, the configuration of FRs was studied. Based on the experiments data, the FRs of PVC was divided into three kinds, and flame retardancy and smoke suppression mechanism mode for each kind of FRs was proposed. All experimental phenomena were well explained by these modes. According to the FRs mixture results, two new kinds of FRs were developed. Mechanochemical modification could greatly increase the flame retardancy and smoke suppression properties and mechanical property. The following are main conclusions of this paper:1 The flame-retardant/ smoke-suppressant (FRs) of PVC may be divided into three kinds. The first is FRs(I), includes the compounds lying in IVB-VIB, such as TiO₂, V₂O₅, Cr₂O₃ and MoO₃; The second is FRs(II), includes the compounds lying in VIIB-IB, such as MnO₂, Fe₂O₃, Co₂O₃, CuO and ZnO. The third is FRs (III), includes the compounds of subgroup A, for example Mg(OH)₂, A1(OH)₃, Sb₂O₃, carbonate and phosphate.2. On-line measurement of conductivity was used to study the effect of transition metal oxides on the kinetics of elimination of HC1 during thermal decomposition of PVC. The experimental results show that the presence of FRs(I) obviously decrease the elimination rate of HC1 and the total output of HC1 by a factor of 10-20 times, indicating that FRs(I) has strong inhibiting effect on the release of HC1. The presence of FRs(II) promotes the elimination of HC1 during thermal decomposition of PVC. Especially the maximum elimination rate of HC1 in PVC/ZnO is about 10 times as high as that of PVC. In this work, kinetic model, Ln(l-a ) = -ktⁿ, is established to describe the kinetics of elimination of HC1 during thermal decomposition of PVC. The elimination of HC1 during thermal decomposition of PVC is divided into two stages. In stage I, the elimination rate of HC1 during thermal decomposition of PVC increases with the rise of the apparent order of reaction, n, in this model, n value of PVC is 3.4, PVC/FRs(I) is 2.8 and PVC/FRs(II) is 5.0. In stage II, n value of PVC is 1.4, PVC/FRs(I) isl.3 and PVC/FRs(II)isl.0.3. Each kind of FRs has its different mechanism of flame retardancy and smoke suppression. For the first kind of FRs, FRs(I), its mechanism can be described as " Complexing Bonds Model ". FRs(I) can strongly suppress the elimination of HC1, raise the on-set temperature of decomposition of PVC, promote the crosslinking during decomposition, reduce the total output of aromatic compounds, increase the gel of condensed phase and char residue, the char residue is loosened. The configuration of FRs(I) has no changed. The mechanism of the second kind of FRs, FRs(II), can be described as "Accelerating the Elimination of HC1 and Crosslinking by Ion Model ". FRs(II) can obviously promote the elimination ofHCl, decrease the on-set temperature of decomposition o...