毕业设计外文文献翻译.docx

1、毕业设计外文文献翻译 毕 业 设 计外 文 文 献 译 文 及 原 文学 生： 学 号： 院 （系）： 机电工程学院 专 业： 材料成型与控制工程 指导教师： 2011 年 6 月 8 日Solid-State Microcellular Acrylonitrile-Butadiene-Styrene FoamsSUMMARYMicrocellular ABS foams are a novel familv of materials with the potential to significantly reduce material costs in a number of applica

2、tions that currently use solid polymer. ABS foams were produced using carbon dioxide in a solid-state process. Solubility and diffusivity of C02 in ABS was measured, and the latter was found to depend significantly on the gas concentration. The useful range of process-space for ABS-CO2 was character

3、ized. Closed cell ABS foams were produced with densities ranging from 1.03 g/cm3 (almost completely solid) to 0.09g/cm3.It was determined that there are many different processing conditions that can produce microcellular ABS foams that have the same density. The cell nucleation density was of the or

4、der of 10 cells per cm3, and the average cell sizes observed ranged from 0.5 um to 5.6 um.INTRODUCTIONABS (Acrylonitrile-butadiene-styrene) has grown to become one of the most widely used thermoplastic in the world because of the wide range of available properties. ease of processing, and a good bal

5、ance between price and performance. ABS is an amorphous copolymer alloy, with acrylonitrile bringing chemical resistance and heat stability, butadiene bringing toughness, and styrene providing good processing characteristics.These qualities provide an excellent engineering thermoplastic that is used

6、 for a wide range of products, including computer housings, automotive interiors, appliances, and building materials. In many applications, the solid ABS can be replaced by relatively high density microcellular foams, since the properties of solid ABS are not fully utilized. Currently, the only proc

7、ess than can produce foams suitable for thin cross-sections is the solid-state microcellular process originally developed at MIT as a way to produce high strength polymer foams which can reduce the amount of material used in manufactured products.This process produces foams with a very large number

8、of very small cells, typically on the order of 10 um diameter, and thus the phase microcellular foams was coined.The batch microcellular process has two stages. In the first stage a thermoplastic sample is placed in a pressure vessel which is then pressurized with a non-reacting gas. Carbon dioxide

9、and nitrogen are typically used as the foaming agents because of their low cost and high solubility in most polymers. The polymer sample absorbs the gas until an equilibrium gas concentration is reached. At this point. the sample is removed from the pressure vessel. In the second stage of the microc

10、ellular process the sample is heated, typically in a hot bath, to induce foaming. The temperature of the hot bath is in the neighbourhood of the glass transition temperature of the polymer, and thus the polymer remains in a solid, or rubbery state, well below the melting point, during the entire pro

11、cess. To distinguish these foams from the common foams made from polymer melts, they are described as solid state foams.The process described above is a batch process used to produce relatively small amounts of foam specimens at a time. The production capability of the solid-state microcellular foam

12、s has increased with the development of the semi-continuous process.In the semi-continuous process the sheet of polymer placed in the pressure vessel is replaced with a roll of polymer which has a gas permeable material rolled up in it to allow gas to diffuse into the entire surface of the roll. The

13、 polymer roll and gas permeable material are first separated, and then the polymer sheet is drawn through a hot bath to foam, and a cold bath if necessary to quench the structure.Microcellular foams can be produced with a wide range of densities and with an integral skid. Due to their potential as a

14、 novel family of materials, a number of polymer-gas systems have been explored in recent years, including polystyrene, polycarbonate, PET, PETC, and PVC.In this paper we present a detailed experimental characterization of the ABS-C02 system, and explore the effects of key process parameters on the m

15、icrostructure.EXPERIMENTALCommercially available Cycolac GPX 3700 ABS, manufactured by General Electric was used in this study. All of the specimens were produced from 1.5 mm thick sheet with natural colour. The unprocessed material has a density of 1.04 g/cm3, and a glass transitions temperature of

16、 about 116.Solubility and diffusivity measurementsSpecimens were cut from 1.5 mm thick sheet to dimensions of 2.5 x 2.5 cm. Each sample was then saturated in a pressure vessel at 26.7 (80F) controlled to 1. The temperature and pressure used to saturate the specimens will be referred to as the satura

17、tion temperature and saturation pressure respectively. The saturation pressure was controlled to within 35 kPa (5 psi). The samples were periodically removed from the pressure vessel and weighed on a precision balance with accuracy of 10ug to determine the amount of gas absorbed. Because the amount

18、of gas absorbed by the samples was on the order of 10 mg, this method provided sufficient accuracy.Desorption measurements were made from fully saturated samples. After reaching equilibrium C02 concentration, the samples were allowed to desorb the C02 while held at 26.7 (80F) and atmospheric pressur

19、e. During the desorption experiments, the samples were weighed on a precision balance to determine the remaining C02 concentration.Foam sample preparation and characterizationSamples were cut to dimensions of 2.5 cm 2.5 cm and saturated in a pressure vessel maintained at 26.7 1 (80F) until an equili

20、brium CO2 concentration was reached. The time required to reach equilibrium was determined from the sorption measurements discussed above. After saturation. all specimens were allowed to desorb gas for five minutes prior to foaming. The same desorption time, 5 minutes, was used for all specimens to

21、ensure that the integral unfoamed skin thickness was negligibly small. After desorption, the samples were foamed by heating in a glycerin bath for a length of time that will be referred to as the foaming time. The temperature of the glycerin bath used to foam the specimens will be referred to as the

22、 foaming temperature. All samples were foamed for five minutes. Once the foaming time had elapsed, the foamed specimens were immediately quenched in a water bath maintained at room temperature. Specific values of the saturation pressures,foaming temperatures, and foaming times will be discussed late

23、r. After foaming, the samples were immersed in liquid nitrogen and then fractured to expose the internal microstructure. The fractured surfaces were made conductive by deposition of Au-Pd vapour and then studied under a scanning electron microscope (SEM). All SEM micrographs were taken along the cen

24、tre-line of the sample. Determination of cell size and cell nucleation densityThe average cell size, cell size distribution, and number of bubbles per unit volume of foam were determined by Saltikovs method described in detail by Undenvood. Saltikovs method allows the characteristics of a three dime

25、nsional distribution of spheres to be estimated from a two dimensional image, such as a micrograph. Previously it was assumed that the fracture plane passed through the centre of all bubbles in a micrograph, introducing a small error in the estimation of the average cell size. cell size distribution

26、, and cell nucleation density. In addition, it was also assumed previously that the number of bubbles per unit volume (i.e. bubble density) could be determined by cubing the line density. Saltikovs method provides a more robust procedure for estimating the bubble density, and is applicable to a wide

27、r range of microstructures. Saltikovs method was implemented by digitizing an SEM micrograph with approximately 200 bubbles, and using NlH lmage to determine the areas of the bubbles. NIH Image is a public domain image processing and analysis program developed at the Research Services Branch (RSB) o

28、f the National lnstitute of Mental Health (NIMH), part of the National Institutes of Health (NIH). The mean bubble diameter and standard deviations reported in this paper are based on the lognormal distribution proposed by Saltikov.The cell nucleation density was determined by a method described pre

29、viously and is the number of bubbles that nucleated in each cm3 of unfoamed polymer. The volume fraction of the bubbles was taken to be the area fraction of the bubbles in a micrograph as suggested by Underwood. The density of each sample was determined by the weight displacement method, ASTM D792.R

30、ESULTS AND DISCUSSIONThe solubility and diffusivity of C02 in ABSFigure 1 shows the gas sorption of CO2 into 1.5 mm thick ABS sheet subjected to saturation pressures of 350 kPa, 1MPa, 2MPa, 3MPa, 4MPa, 5MPa, and 6MPa at a saturation temperature of 26.7 (80F). The CO2 concentration in mg gas/g polyme

31、r is plotted vs time. Over time, the concentration of CO2 increases within the polymer until the polymer absorbs no more gas and can be considered saturated. As expected, the concentration of gas at equilibrium increases as the saturation pressure is increased. For the ABS formulation studied here,

32、equilibrium concentrations as high as 150 mg C02/g polymer were achieved at a saturation pressure of 6 MPa. Figure 1 also shows that the diffusion of CO2 in ABS isFigure 1 Sorption curves for 1.5 mm thick ABS in CO2 at 26.7 (8OF), and pressures ranging from 350kPa to 6MPa. Increasing saturation pressures result in short er saturation times and higher equilibrium concentrations dependent on gas pressure. We see that it takes approximately 50 hours to reach equilibrium at a saturation pressure of 3 MPa, while at 6 MPa the equilibrium is reached in 20 hours. The faster diffusion at 6 MPa