PVDF resists most organic and inorganic chemicals including chlorinated solvents. Poly(vinyl fluoride) is a semicrystalline polymer with a planar, zigzag conformation. The degree of crystallinity can vary significantly from 20 to 60% and is a function of defect structures.
PVDF Properties
Polyvinylidene fluoride is a semicrystalline polymer (35e70% crystallinity) with an extended zigzag chain.Head-to-tail addition of VDF dominates but there are headto-head or tail-to-tail defects that affect crystallinity and properties of PVDF.
PVDF has a number of transitions and its density alters for each polymorph state. There are four known proposed states, named as a, b, g, and d. The most common phase is a-PVDF which exhibits transitions at 70 C (g), 38 C(b), 50 C (a”), and 100 C (a’).
PVDF resists most organic and inorganic chemicals including chlorinated solvents. Strong bases, amines, esters, and ketones attack this resin. The impact ranges from swelling to complete dissolution in these solvents depending on the conditions. PVDF exhibits compatibility with a number of polymers. Commercially useful blends with acrylics and methacrylics have been developed.
PVDF, just as ETFE, readily crosslinks as a result of exposure to radiation. Radiation (gamma rays) has modest effect on the mechanical properties of PVDF.
PVF Properties
Poly(vinyl fluoride) is a semicrystalline polymer with a planar, zigzag conformation. The degree of crystallinity can vary significantly from 20 to 60% and is a function of defect structures. Commercial PVF is atactic, contains approximately 12% head-to-head linkages, and displays a peak melting point of about 190 C.
PVF displays several transitions below the melting temperature. Lower Tg occurs at 15 to 20 C and upper Tg is in the 40e50 C range. Two other transitions at 80 C and 150 C have been reported.
PVF has low solubility in all solvents below about 100 C. Polymers with greater solubility have been prepared using 0.1% 2-propanol polymerization modifier and were characterized in N,N-dimethylformamide solution containing 0.1 N LiBr. Mn ranged from 76,000 to 234,000 (osmometry), and Ms from 143,000 to 654,000 (sedimentation velocity).
High molecular weight PVF is reported to degrade in an inert atmosphere, with concurrent HF loss and backbone cleavage occurring at about 450 C. In air, HF loss occurs at about 350 C, followed by backbone cleavage around 450 C.
PVF is transparent to radiation in the UV, visible, and near-infrared regions, transmitting 90% of the radiation from 350 to 2500 nm. PVF becomes embrittled upon exposure to electron-beam radiation of 1000 Mrad but resists breakdown at lower doses. It retains its strength at 32 Mrad while PTFE is degraded at 0.2 Mrad.
The self-ignition temperature of PVF film is 390 C. The limiting oxygen index (LOI) for PVF is 22.6%. HF and a mixture of aromatic and aliphatic hydrocarbons are generated from the thermal degradation of PVF.
Post time: Apr-04-2018