Abstract
Flame-retardant polyvinyl alcohol (PVA) membranes with high transparency and flexibility were prepared by mixing an aqueous solution of a phosphorus-containing acrylic acid (AOPA) with PVA. The reaction between AOPA and PVA, the transparency, the crystallinity and the flexibility of the membrane were investigated with Fourier transform infrared spectrometry (FTIR), UV–vis light transmittance, X-ray diffraction and tensile tests, respectively. The limited oxygen index (LOI) and vertical flame (UL 94 VTM), microscale combustion calorimetry, thermogravimetric analysis (TGA) and TGA-FTIR were employed to evaluate the flame retardancy as well as to reveal the corresponding mechanisms. Results showed that PVA containing 30 wt% of AOPA can reach the UL 94 VTM V0 rating with an LOI of 27.3% and retain 95% of the original transparency of pure PVA. Adding AOPA reduces crystallinity of PVA, while the flexibility is increased. AOPA depresses the thermal degradation of PVA and promotes char formation during combustion. The proposed decomposition mechanism indicates that AOPA acts mainly in the condensed phase.
Highlights
Polyvinyl alcohol (PVA) is a biocompatible and biodegradable polymer
For the inorganic-based flame-retardant PVA, dispersing additive in the matrix on the nanoscale can maintain the transparency of PVA
Organic additives having an interaction with PVA by chemical bonding or hydrogen bond are a better option to maintain the transparency of polymer when improving the flame retardancy [7,19,20] than the inert organic additives
Summary
Polyvinyl alcohol (PVA) is a biocompatible and biodegradable polymer. Good film formation, high transparency and mechanical properties make PVA films widely used in the textile industry, furnishings, adhesives and packaging materials [1–3]. For the inorganic-based flame-retardant PVA, dispersing additive in the matrix on the nanoscale can maintain the transparency of PVA. Nanoparticles aggregate with each other; it is difficult to disperse them in the polymer at the concentration which meets the flame retardancy requirement. Organic additives having an interaction with PVA by chemical bonding or hydrogen bond are a better option to maintain the transparency of polymer when improving the flame retardancy [7,19,20] than the inert organic additives. These reactive additives can mix with the matrix at a molecular level by chemical bonding if the polarity and solution parameters of the additives are close to that of the polymer. Compared with reactive halogen-containing additives, phosphorus-containing compounds are more reliable and safer due to release of non-toxic gases and less smoke during combustion [21–23]
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