学术英语写作课程论文

研究生学术英语写作课程论文

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Abstract

Using butyl methacrylates(BMA) as monomer, Span80 as emulsifier, divinyl benzene (DVB) as cross-link agent, ammonium persulfate(APS)/sodium hydrogensulfite(SHS) as redox initiator, the high oil-absorption resin was synthesized by concentrated inverse emulsion polymerization. And the effects of different polymerization technological parameters, such as initiator, crosslinker, emulsifier, on the oil absorbency of high oil-absorption resins were discussed in detail. The result indicated that the absorption of the resin was about (g/g) for and (g/g) for chloroform.

Key words: concentrated inverse emulsion polymerization；oil absorption resin；oil absorption rate

摘要

以甲基丙烯酸正丁酯为单体，二乙烯基苯为交联剂，Span80为乳化剂，过硫酸铵/亚

硫酸氢钠为氧化还原引发剂，采用超浓反相乳液法合成了高吸油性树脂。研究了引发剂用量，交联剂用量，乳化剂用量对树脂吸油性能的影响。所制备的树脂可以吸收自身重倍的甲苯、倍的三氯甲烷。

关键字：超浓反相乳液聚合；吸油性树脂；吸油速率

Contents

1

3

3

3

3

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4

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4 5

5

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6

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8

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10

11

1 Introduction

Oil pollution of marine environments is becoming a serious issue. With the growth of the off-shore petroleum industry and the necessity of marine oil transportation. Various methods for the treatment of spilled oil have been tried[1–5]. One of the methods to solve this problem is by using oil absorptive resins, which can collect and remove the oil spilled on water, and some have proved to be highly efficient[6-7].

High oil-absorption resin, being different from traditional oil-absorbing materials, is a new kind of self-swelling oil-absorbing material with many virtues of absorbing large quantity and variety of oils, only absorbing oil from oil/water mixture and high capacity for oil retention, and has a promising future. Synthesis and applications of high oil-absorption resins have very important practical significance for environment protection.

Acrylic has been widely used as monomers to prepare high oil-absorbing resins. Copolymerization of acrylic can be approached by various methods such as emulsion polymerization and suspension polymerization. However, the resins obtained by the above methods universally have some defects of compact structure[8–10]. It is important to select a

suitable technique and optimize the conditions of polymerization for synthesis of workable acrylic copolymer.

Concentrated emulsions are gel-like emulsions in which the volume fraction of the dispersed phase is greater than . The dispersed phase is in the form of spherical or polyhedral cells separated by a continuous-phase network of thin films. Concentrated emulsions have three important characteristics:[11-12] (1) the reduced monomer mobility between cells, because of the presence of a reinforced surfactant layer, can generate an earlier gel effect, which leads to a delay in the bimolecular termination reaction and, therefore, a higher molecular weight; (2) the particle size can be controlled easily by the selection of a suitable surfactant type and concentration; and (3) a polymer containing little water, from which powdery resins are easily formed, can be obtained through concentrated emulsion polymerization.

In comparison with the four methods of free-radical polymerization (bulk, solvent, suspension, and emulsion), concentrated emulsions have not only a paste like appearance and a high solid content but also a nucleation mechanism for the latex particle; the morphology of latex products is different from that of conventional emulsion polymerization. For these reasons, concentrated emulsion polymerization deserves to be studied deeply and widely. In this , the influences of emulsifiers，the amount of cross-link agent, the amount of initiator on the absorption properties of the resin were investigated．

2 Experiment

Materials

Butyl methacrylate(BMA) analytical reagent grade, Tianjin Kedi Reagent, was used as monomer ; Ammonium persulfate(APS) and sodium hydrogensulfite(SHS) analytical reagent grade, Tianjin Fuchen Reagents, were used as redox initiator; Span80 analytical reagent grade, Tianjin kemio Reagent, was used as emulsifier; Divinyl benzene(DVB) chemically pure, Shangha Reagent , was used as cross-link agent.

Polymerization

BMA was carried out in 150-ml roundbottom flask. A typical procedure was as follows: the required amounts of Span80 and DVB were put into the reaction system.

The system was charged with N

2 for 20 mins and was sealed under N

2

. Then 32-ml

deionized water was injected into the reaction system. After that, ammonium persulfate(APS)/sodium hydrogensulfite(SHS) were injected into the reaction system. The flask was wholly immersed in a water bath held at 40 ℃ by a thermostat to start the polymerization. The reaction was carried out under stirring. The reaction time was 3 h. The polymer was dried in vacuum for 24 h at a 35℃.All of the ingredients used are summarized in Table 1.

Table 1. Standard recipe for the concentrated inverse emulsion

polymerization of BMA

Ingredient Dosage BMA7ml

DVB

Span80

H

2

O32ml

（NH4)

2S

4 O

8

NaHSO

3 Measurements

Oil absorption test (g

oil /g

sample

)

The oil absorbency (W) was determined by the weighing method. A quantity of ~ g of dried sample weighted beforehand was put into a filter bag and immersed in toluene at room temperature. After given time periods (24 h is needed for full oil absorbency), the filter bag with the sample was lifted from the oil and drained for 1 min. Then the sample was immediately taken out and weighed. The oil absorbency was calculated by the following formula:

W 1=( G

2

- G

1

)／G

1

where G

1is the weight of resins before oil absorption and G

2

is the weight of resins

after oil absorption.

For the study of oil absorption rate of the resins, the above measurements are repeated from time to time.

Regeneration test

Oil-absorbed samples were dried in vacuum for 24 h. Using the above measurements tests oil absorbency at five times.

Oil retention

The resins after oil absorption were put in drying oven for 5 h at 50℃, and then weighted.

Characterization

The particle morphology of the BMA polymer was observed with scanning electron microscopy (SEM; JSM-5610LV). The samples were sputter-coated with Au film before the examination and the voltage is 20 kV.

3 Results and Discussion

The effect of cross-linking amount on the oil absorbency The oil-absorbing process of high oil-absorption resins, as low degree of polymer, was swelling process. As evidence, not only the sorts of crosslinker can affect the interstitial space structures of the resins, but also the amount of crosslinker can directly influence the particle morphology and the degree of crosslinking of the resins. Figure 1 illustrated the relationship between oil absorbency and the amount of DVB. As shown in Fig. 1, there was a maximum point. When the amount of DVB was smaller than that at the maximum point, the oil absorbency increased with increasing DVB. However, the oil absorbency decreased with increasing DVB when the mount of DVB was larger than that at the maximum point.

The effect of cross-linking amount on the oil absorbency It is well known that an increase in the amount of a crosslinker causes the denser network of the polymer. Adding less amount of DVB, the degree of crosslinking of the resins was lower, the tridimensional network was not satisfying. The resins were soluble in oil and the viscosity of the product increased. The resins which have absorbed oil cannot recover. If the amount of crosslinker was too great, the crosslinker degree increased and the network space in the resins decreased. As a result, the oil absorbency reduced. The resins had the best oil absorptivity when the interstitial space is at its optimum value. Figure. 1 shows that this occurs at .

Effect of the amount of the emulsifier on the oil absorbency In concentrated inverse emulsion polymerization, although emulsifiers do not directly take part in the reaction, they have reducing interface tension, emulsification, and dispersing effects. The main difference with a conventional emulsion polymerization is that a part of emulsifier is present at the

monomer/water interface and not only at the polymer particle/water interface. Another point is that, in most cases, the amount of the emulsifier is very low, so that the particles formed by the emulsion process are not stable enough and easily coalesce to give much larger primary particles.

The effect of Span80 concentration on the oil absorbency

The effect of initiator amount on the oil absorbency

BMA polymer as short-chain high oil-absorption resins were prepared by concentrated inverse emulsion polymerization, with the formation of radicals in water phase, and the radicals were captured by the existing particles inside the water phase. The effects of various APS and SHS concentrations based on the weight of BMA on the oil absorbency were shown in Fig. 3

With increasing initiator concentration, the oil absorbency increased, and then decreased. The concentration of APS and SHS needed to be in a certain range to ensure that the reaction proceeds smoothly.

The effect of initiator amount on the oil absorbency In the reaction system, the concentration of the initiator will cause effects on the reaction rate, the molecular weight of the resins, and the crosslinking degree. Moreover, it is known that the more initiator will generate more active centers in order to increase the conversion and the gel fraction and decrease the length of the basic chain in polymer systems. As a result, the chain length between crosslinking points of the network decreased and the crosslink density increased with the increase of the initiator concentration. Therefore, the final result was a decrease of the oil absorbency.

Oil absorption rate of the resins

The SEM microphotographs of particles prepared by concentrated inverse emulsion polymerization was displayed in Fig. 4. It was apparent that there were many small random pores in the crosslinked resins prepared by concentrated inverse emulsion polymerization. These pores will support large surfaces in the polymeric network. The morphology of a crosslinked resins will influence the rate of oil absorption.

The oil absorption rate of the resins is shown in . At first, the speed rate of the oil absorption was very fast at first 30mins. Obviously, it only need 2h to the highest oil absorbency.

SEM microphotographs of particles prepared by concentrated inverse

emulsion polymerization

Oil absorption rate of the resin

Relation of oil retention ratio with time

The resins after oil absorption were put in drying oven for 5h at 50℃, and then weighted. The result of oil retention was in Table 2.

Relation of oil retention ratio with time

Time(h)12345 Prue oil (%)

Oil

retention

rate of resin

(%)

Oil absorption repetitive characteristic of resins

The result of oil absorption repetitive characteristic of resins was in Fig. 6.

Oil absorption repetitive characteristic of resins

4 Conclusions

BMA polymer as short-chain high oil-absorption resin was synthesized by concentrated inverse emulsion polymerization. The effects of the concentration of the crosslinker, the concentration of the initiator, and the amount of the emulsifier on the oil absorbency were discussed. The optimum polymerization

conditions were obtained as follows:

m DVB /m

monomer

=%, m

(APS/SHS)

/m

monomer

= wt%, m

Span80

/m

monomer

=8wt%; The highest oil absorbency was

g/g for and g/g for chloroform. The speed rate of the oil absorption was very fast at first 30mins,and it only need 2 h to the highest oil absorbency. Bibliography

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