Mechanical, Diffusion and Degradation Behaviour of Polypropylene and Cellulose Blends
Korir, Patrick Kiprono
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Polypropylene is one of the most important commodity polymers and is used in many areas. Its applications are often limited due to its low impact strength, Young‟s modulus properties and non-biodegradability nature. Blending polypropylene with different polymers is an economic and effective way to improve these drawbacks. Polypropylene/wood flour blends have undesirable properties; they have weak structural rigidity, very low thermal stability and high diffusivity. Cellulose is linear, rigid and has a higher thermal stability and diffusivity hence effective in reinforcement of polypropylene and high density polyethylene. In this research a series of experiments have been conducted. Samples blends of polypropylene reinforced with cellulose were prepared by melt mixing followed by injection molding. The study deals with the effect of cellulose on Dynamic mechanical, creep, degradation and diffusion properties of polypropylene and its cellulose blends. Dynamic mechanical analysis was carried out in the frequency and temperature range of 1 to 30 Hz and -30 to 120 oC respectively. The effects of cellulose concentration on relaxation processes were investigated. Two relaxation processes (α and β) were observed. The α process was assigned to main chain motion while β process was a local process due to interlamellae shearing. Relaxation frequency showed overlaps with cellulose intake confirming that cellulose loading has no effect on free volume for relaxation processes, hence overlapping Vogel temperature (To). Vogel Fulcher Tamman (VFT) equation was used to analyze the data. Creep measurements were performed at 30, 40, 50 and 60 oC. The time for deformation and recovery of the samples were 12 minutes each. Creep deformation of the samples decreased with cellulose loading. Time temperature superposition was used to predict the long time experiment up to approximately 104 seconds. Shift factors obeyed the William Landel Ferry (WLF) model hence; the deformation was dependent on free volume. Thermal degradation analysis was carried out using Lindberg Blue tube furnace within a temperature range of 25 to 550 oC at a heating rate of 5 oC/min. Two decomposition stages corresponding to polypropylene and cellulose decomposition were observed. Thermal stability of the blends decreased with cellulose loading (thermal activation energy decreased from 70.0 to 40.6 kJ/mol). Broido equation was used to analyze the data. Diffusion measurements were done at room temperature and mass differences were monitored after 1, 7, 30, 60, 90 and 120 days. The test specimens were removed from the test liquid one at a time. Diffusion coefficients increased from 4.89 x 10-10 to 4.21 x 10-8 cm2s-1 with cellulose loading. Fick‟s second law was used for data analysis. Biodegradation measurements were also done by burying the dried samples in soil at a depth of 20 cm behind the physics laboratory in Kenyatta University main campus. Samples were removed after 1, 7, 30, 60, 90, 120 and 150 days. The rate of biodegradation increased with cellulose intake from 20,000 to 5 years due to increase in hydrophilicity. Regression line method was used to analyze the data. Use of cellulose as a blend on polypropylene should be adopted to improves its mechanical properties and minimize environmental pollution.