共查询到20条相似文献,搜索用时 46 毫秒
1.
Processing of microcellular foam was studied for polyurethane. Assuming that the bubble growth is controlled by diffusion, theoretical prediction was carried out numerically to understand the bubble growth mechanism in the cavity during mold filling. Final bubble sizes were also predicted by considering the gelation time and the diffusion boundary. Viscosity change of the mixed polyurethane resin during polymerization reaction was predicted by considering reaction kinetics. The gelation time was determined to terminate the numerical calculation. The diffusion boundary was predicted based on the number of nucleated bubbles that had been determined both theoretically and experimentally. For processing of polyurethane foam by reaction injection molding, ultrasonic excitation was applied to the mixture of polyol and isocyanate. The polyol resin was supersaturated with nitrogen gas at an elevated pressure and ultrasonic excitation was applied to the mixture after impingement mixing of two components of the selected polyurethane system. Bubble nucleation was induced by the ultrasonic excitation and the bubbles were grown as the gas was supplied to the bubble from the resin. 相似文献
2.
A study on the apparent thermal conductivity of polyurethane foam was carried out. A HCFC (hydrochlorofluorocarbon) gas and carbon dioxide were used as the physical blowing agent and ultrasonic excitation was applied to increase the rate of bubble nucleation. The thermal conductivity of the binary gas mixture was predicted theoretically to estimate the apparent thermal conductivity of the polymer foam. Effects of conduction and radiation on the apparent thermal conductivity of the cellular polyurethane were considered with respect to the cell size and the effect of convection was neglected because of the small cell size. A laboratory RIM machine was designed and built for foaming experiments. The foaming experiments were performed at various processing conditions, and density, apparent thermal conductivity, number of cells, and cell sizes were measured. Best results such as low thermal conductivity and small bubbles were obtained when the polyol was mixed with the HCFC gas and saturated with carbon dioxide at 0.3 MPa, and foamed with ultrasonic nucleation. 相似文献
3.
Ultrasonically induced bubble formation for the production of thermoplastic foam was investigated experimentally and theoretically as a basic study. A general purpose polystyrene and blends of low density polyethylene and polyethylene wax were saturated with nitrogen gas under various pressures and the ultrasonic excitation was applied to the polymer system upon release of gas pressure. The ultrasonic nucleation of bubbles in the polymer matrix was modeled by utilizing the classical nucleation theory. The negative pressure generated by the ultrasonic excitation was considered as the environmental pressure at the moment of nucleation. The experimental results showed that the heterogeneous nucleation must be used for ultrasonic foaming of the viscous fluid and the homogeneous nucleation for the low viscosity fluid. The theoretical analysis also indicated that the ultrasonic nucleation can be applied to the production of thermoplastic foam if the ultrasonic excitation generates large enough negative pressure. 相似文献
4.
自制聚酯多元醇,以此多元醇为基础多元醇合成聚合物聚酯多元醇(TPM),考察了TPM对聚氨酯微孔弹性体力学性能等方面的影响.结果表明,自制的聚酯多元醇合成的TPM能够有效改善微孔弹性体产品的硬度、拉伸强度等力学性能,使泡孔均匀细致,表皮光滑,提高了产品尺寸稳定性和成品率. 相似文献
5.
为提高双组分水性聚氨酯的室温交联速度,将 N-苄基乙醇胺引入到环氧树脂制备了环氧树脂基水性多元醇,表征了多元醇的化学结构,并测定了其相对分子质量、粒径分布和玻璃化温度等主要技术参数。将环氧树脂基水性多元醇与多异氰酸酯配合制备了双组分水性聚氨酯,采用红外光谱法研究了室温交联反应过程。研究结果表明:多元醇分子结构中引入苄胺基加快了双组分水性聚氨酯的交联反应速度。将双组分水性聚氨酯制备成水性木器涂料,漆膜具有优异的耐冲击性、附着力、柔韧性、光泽、耐液体介质、硬度、丰满度等性能。 相似文献
6.
A new method of producing microcellular polyester composites is developed. The microcellular foam which is produced by supersaturating the polyester resin with nitrogen is cured by dielectric heating. The lightweight composite contains about 10 μm size bubbles. By substituting the microcells for the particulate fillers of the conventional composites, the weight of the composite is reduced by 30 to 40 percent. A theoretical analysis based on classical nucleation theory is applied to predict the rate of nucleation. The diffusion controlled bubble growth is modeled and the theoretical prediction is in good agreement with experiment. The mechanical behavior of the microcellular composite has also been examined. Toughness is improved significantly whereas the flexural strength remains the same as that of a conventional sheet molding compound. 相似文献
7.
对聚合物多元醇在聚氨酯微孔弹性体中的应用进行了研究。考察了聚合物聚醚多元醇及聚合物聚酯多元醇对聚氨酯微孔弹性体力学性能的影响。实验结果表明,该类聚合物多元醇的引入可使聚氨酯微孔弹性体制品的力学性能得到较大改善,因此该类聚合物多元醇在聚氨酯领域必将具有广阔的应用前景。 相似文献
8.
环氧改性聚酯聚醚型水性聚氨酯的合成及性能研究 总被引:1,自引:0,他引:1
选用环氧树脂E-44为改性剂,以异佛尔酮二异氰酸酯(IPDI)、聚醚多元醇(PPG-220)、聚酯多元醇(POL-220)、二羟甲基丙酸(DMPA)等为主要原料合成了一系列环氧树脂改性的水性聚氨酯乳液。探讨了聚酯多元醇、DMPA和环氧树脂加入量对乳液和膜性能的影响。通过傅里叶变换红外光谱(FT-IR)、接触角及拉伸测试研究了改性树脂的结构、耐水性和力学性能;通过差示扫描量热法(DSC)和热重(TG)分析研究了聚合物膜的热性能。实验结果表明:当w(聚酯)=20.0%,w(DMPA)=3.9%,w(E-44)=8%时,获得综合性能优良的改性水性聚氨酯。 相似文献
9.
A batchwise process for the production of microcellular plastics was studied in the polystyrene–nitrogen system. The effects of saturation temperature, saturation pressure, and late‐ and quick‐heating on the microcellular structure were investigated by considering the solubility of the gas in the polymer. It was found that the mean cell diameter was reduced and the cell number density increased with increase in the gas solubility. Variation in the saturation temperature showed that the cell number density had a minimum and the mean cell diameter had a maximum at about 350 K, which was related to the minimum solubility of nitrogen in polystyrene. The long heating time at 393 K of a solution saturated under 25 MPa increased the cell diameter, reduced the cell number density, and gave a maximum volume expansion ratio at about 300 s. Further heating caused the cell size and volume expansion ratio to be decreased, which might be caused by diffusion of the gas out of the polymer sample. The effect of the saturation temperature under high saturation pressure on the cell number density was qualitatively well predicted by the nucleation theory. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2383–2395, 2000 相似文献
10.
11.
微孔塑料挤出成型中气泡成核的聚合物刷子模型 总被引:4,自引:0,他引:4
气泡成核是微孔塑料连续挤出成型中的关键步骤之一,临界气泡核直径是影响制品中泡孔直径的主要因素,成核密度则是影响制品泡孔密度的主要因素,但现有的成核理论大都是以经典成核理论为基础的,而经典成核理论虽然人出了临界气泡核及成核速率的计算公式,但并没有考虑到聚合物的物性参数,并且不能计算临界气泡核半径的具体数值,所以其应用有很大的局限性,从聚合物刷子模型出发建立气泡成核的刷子模型,从而得出临界气泡核半径的计算公式,并分析温度,压力,聚合物相对分子质量等对临界气泡核半径的影响。 相似文献
12.
13.
Microllular plastics are cellular polymers characterized by cell densities greater than 109 cells/cm3 and cells smaller than 10 μm. One of the critical steps in the continuous production of microcellular plastics is the promotion of high cell nucleation rates in a flowing polymer matrix. These high nucleation rates can be achieved by first forming a polymer/gas solution followed by rapidly decreasing the solubility of gas in the polymer. Since, in the processing range of interest, the gas solubility in the polymer decreases as the pressure decreases, a rapid pressure drop element, consisting of a nozzle, has been employed as a continuous microcellular nucleation device. In this paper, the effects of the pressure drop rate on the nucleation of cells and the cell density are discussed. The experimental results indicate that both the magnitude and the cell density are discussed. The experimental results indicate that both the magnitude and the rate of pressure drop play a strong role in microcellular processing. The pressure phenomenon affects the thermodynamic instability induced in the polymer/gas solution and the competition between cell nucleation and growth. 相似文献
14.
为拓宽微孔注塑制品的应用范围,需要改善其表面质量,降低其翘曲变形。模腔气体反压技术、模腔被动控温技术、微孔共注塑技术、泡孔成核速率控制技术、微孔注射压缩成型技术和快速热循环微孔注塑技术等可有效改善微孔注塑制品的表面质量。模腔气体反压技术、微孔共注塑技术和调整加工参数可进一步降低微孔注塑制品的收缩率和翘曲,提高制品的尺寸精度。本文较系统介的绍了这些技术和方法。 相似文献
15.
16.
In this study, we explore the use of solid‐state nucleation in polymer pellets as a means to create microcellular PLA foams in extrusion. This is achieved by using gas‐saturated PLA pellets as input to the extruder. Foam density, bubble size, and bubble density is reported and compared with microcellular foams created in the gas‐injection extrusion process. PLA pellet gas concentrations between 17 and 29 mg CO2/g PLA was found to produce quality microcellular foams in this process. Gas concentrations within this range were achieved by varying methods that included partial saturation, desorption from full saturation, and blending saturated with unsaturated pellets. This gas concentration window that produced microcellular foams was found to be independent of the saturation and desorption process used to achieve the desired concentration. We further compare the pressure drop and pressure drop rate of the gas‐saturated pellet extrusion process showing that similar foams can be produced at pressures orders of magnitude lower than the alternative gas‐injection extrusion processes. Investigations into extrusion pressures support the hypothesis that the gas‐saturated pellet extrusion process utilizes solid‐state nucleation in the feed section of the extruder to achieve high bubble density foams. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
17.
18.
Mingjun Yuan Lih‐Sheng Turng Daniel F. Caulfield 《Polymer Engineering and Science》2006,46(7):904-918
This article presents the effects of nanoclay and supercritical nitrogen on the crystallization and thermal behavior of microcellular injection‐molded polyamide‐6 (PA6) nanocomposites with 5 and 7.5 wt% nanoclay. Differential scanning calorimetry (DSC), X‐ray diffractometry (XRD), and polarized optical microscopy (POM) were used to characterize the thermal behavior and crystalline structure. The isothermal and nonisothermal crystallization kinetics of neat resin and its corresponding nanocomposite samples were analyzed using the Avrami and Ozawa equations, respectively. The activation energies determined using the Arrhenius equation for isothermal crystallization and the Kissinger equation for nonisothermal crystallization were comparable. The specimen thickness had a significant influence on the nonisothermal crystallization especially at high scanning rates. Nanocomposites with an optimal amount of nanoclay possessed the highest crystallization rate and a higher level of nucleation activity. The nanoclay increased the magnitude of the activation energy but decreased the overall crystallinity. The dissolved SCF did not alter the crystalline structure significantly. In contrast with conventionally injection‐molded solid counterparts, microcellular neat resin parts and microcellular nanocomposite parts were found to have lower crystallinity in the core and higher crystallinity near the skin. POLYM. ENG. SCI., 46:904–918, 2006. © 2006 Society of Plastics Engineers 相似文献
19.
以苯酐、二甘醇、新戊二醇为原料,合成了苯酐聚酯多元醇。简述了合成聚酯多元醇的工艺,对反应温度、醇酸物质的量比、真空度、出水速率和催化剂等对合成聚酯树脂的影响进行了探讨,结果表明,当控制反应温度在250℃左右,醇酸物质的量比为1.164,真空度>0.09MPa,出水速率为50mL/h,催化剂质量分数为0.04%时,合成的苯酐聚酯多元醇能够满足生产聚氨酯胶黏剂的应用要求。并对所做聚酯用红外光谱和核磁共振氢谱表征。 相似文献