Cailiao gongcheng (May 2024)
PHB-modification in PEG/PMMA binder for improving titanium powder injection molding process
Abstract
During metal injection molding (MIM), water-soluble polyethylene glycol (PEG) and polymethyl methacrylate (PMMA) binder system usually lead to the formation of a large number of holes. The time spent in injection demolding increases with the size increasing of the parts for the poor thermal conductivity of the binder system. Poly (β-hydroxybutyrate)(PHB) was used as a PEG crystallization inhibitor to solve this problem. The effects of PHB content on the thermal conductivity, crystallization behavior, rheological properties of the binder, injection holding time and microstructure of the green body were studied by thermal conductivity meter, DSC, rheological experiments and fourier transform infrared spectroscopy (FTIR). The results show that in PHB / PEG blends, with the increase of PHB content, the crystallization temperature decreases from 55.18 ℃ (pure PEG) to 51.4 ℃ (25% PHB modified, mass fraction, the same as below). With the increase of PHB content from 0%-25%, the melting enthalpy and thermal conductivity of PEG blends gradually increase from 79.5 J/g to 107.6 J/g and from 0.2433 W·m-1·K-1 to 0.3469 W·m-1·K-1, respectively. The increasing of binder crystallinity leads to the improvement of thermal conductivity. Due to the complex hydrogen bond interaction in the PEG/PHB/PVAc ternary system, the crystallization temperature of the binder decreases from 50.07 ℃ of pure PEG to 43.3 ℃ of PEG with 25% PHB. The relationship between the viscosity and shear rate of the feedstock prepared with 15% PHB modified PEG binder conforms to the law of power-law fluid. And the shear thinning index of the feedstock prepared with 15% PHB modified PEG binder decreases from 0.77 of pure PEG to 0.62 at 120 ℃.Under the same injection conditions, the injection demolding time is significantly shortened from 100 s (unmodified) to 50 s of PEG with 15% PHB. Meanwhile, the injection green body, with smooth surface, few and uniform distribution internal holes can be obtained using 15% PHB modified PEG binder.
Keywords
