Preparation Of High-Molecular-Weight PVA And Its Affects On The Mechanical Properties Of Ice

The key aim of this thesis is to do primary research in photo-initiated bulk polymerization of VAc and the mechanical properties of ice strengthened by HMWPVA.Firstly the thesis studied photo-initiated bulk polymerization of VAc. The principle of this study is that light intensity attenuates with the increasing of distance to the light-source because of the self-shield effect, so the photo-initiator with the same concentration irradiated by UV light of different intensity creates a free radical concentration gradient along the light irradiation direction. The low-voltage Hg lamp and Irgacure 184 were respectively employed as the light-source and initiator to prepare ultra high molecular weight PVAc. The experimental results indicated that gradient effect really exists within the free radical polymerizing system of VAc , that is, the molecular weight increases while the conversion decreases along the UV light irradiation direction. The highest molecular weight of PVAc obtained is 1.48 million. The factors influencing the molecular weight of gradient polymerization initiated by UV of VAc were investigated. The molecular weight of PVAc can increase effectively by choosing suitable initiator concentration.Then, high-molecular-weight PVA was prepared by saponification of the prior synthesized UHMWPVAc. The mechanical properties of ice strengthened by different concentration of HMWPVA were measured, the results showed that the addition of 1-4% (mass fraction) HMWPVA improved the mechanical properties of ice greatly. When the addition amount of HMWPVA was 3% (mass fraction), the tensile strength, elongation at fracture and compressive strength of ice reached the maximum, and the compressive modulus approached the maximum, and these mechanical properties values are 11.7, 3.5,2.3, 2.1 times of control runs of pure ice respectively. The tensile and compressive properties of the ice strengthened by 3% HMWPVA were compared with the control runs of ice strengthened by 5% and 10% PVA-124 and the PVA molecular weight influenced the tensile property of ice greatly, but influenced the compressive property of ice weakly. The addition of PVA had little influence on the impact strength at the experimental temperature range. Furthermore, the addition of HMWPVA increased the melting time of the ice at ambient.