Analysis of the factors influencing the properties

2022-08-24
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Analysis of factors affecting the properties of urea formaldehyde resin, a high molecular material for modified thermoplastic elastomer (I)

preface

urea formaldehyde resin adhesive is one of the polymer adhesives developed and applied earlier. It has the advantages of simple production process, wide source of raw materials, low cost, convenient use and so on. It is an adhesive widely used in bamboo and wood processing, paper bonding, toughened coating and other industries. With the development of wood industry, the amount of urea formaldehyde glue is very large, but there are also shortcomings such as high content of free formaldehyde, brittleness and so on

in recent years, the properties of urea formaldehyde resin adhesive have been greatly improved through a lot of modification work on urea formaldehyde resin adhesive at home and abroad. Here, we choose oxidized starch to carry out the experimental research on the modification of urea formaldehyde adhesive. Due to the complex influencing factors of urea formaldehyde resin modification experiment, the experimental results are accidental, and some irrelevant variables will be inadvertently introduced into the obtained data, thereby increasing the number of variables. The principal factor analysis method can analyze and process a large number of experimental data, condense information, and reasonably combine relevant variables, so as to reduce variables, straighten out the number of production management processes, eliminate unimportant factors, and find out important information and laws. Using the principal factor method to analyze the influence of some factors on the specific properties of modified urea formaldehyde resin has important guiding significance for further research, improving the process and formula in the production process, and improving the properties of urea formaldehyde adhesive

1 experimental part

1.1 reagents and instruments

500ml ground three neck bottle and other glass instruments, a set of water bath device: 25W mixer: BP-II 500g tray balance; TS type analytical balance, etc

urea, 95% (Lutianhua); Formaldehyde, 36% (SVW); Chemically pure hexamethylene tetramine ((CH2) 6n4); Starch, etc

1.2 synthesis process

1.2.1 preparation of ordinary urea formaldehyde resin

add a certain amount of hexamethylene tetramine into a three neck bottle and start water bath heating. When the temperature rises to 55 ℃, add 40g of the first batch of urea (accounting for 40% of the total urea). When the reaction reaches a certain pH value, add 50g of the second batch of urea (accounting for 50% of the total urea), and maintain a certain pH value (adjusted with acid or alkali). When the reaction reaches the viscosity required for vehicle lightweight, which is mainly reflected in the optimal design of vehicles, the utilization of alloy materials and non-metallic materials, adjust the pH to 6.7, add the remaining 10g of urea, and adjust the pH value to 8 after 20min base note to cool down and discharge

1.2.2 preparation of oxidized starch modified urea formaldehyde resin

after the second batch of urea is put into production, oxidized starch will be put into production immediately. In this experiment, the input of oxidized starch is 30% of the total amount of urea (calculated by dry starch)

2 results and discussion

in view of the large amount of experimental data and many influencing factors, this work adopts the principal factor analysis method to eliminate non relevant variables and condense information. Experimental data processing according to the experimental data and the main factor analysis target design matrix, in this work, matlab5.3 programming is used to standardize the designed initial matrix, calculate the correlation matrix of the standard matrix, obtain the eigenvectors and eigenvalues, and arrange the eigenvalues in descending order. When the cumulative percentage of the first n eigenvalues is greater than 95%, the remaining eigenvalues are omitted, and the initial factor load matrix is obtained, Then the variance maximum orthogonal rotation is performed on the matrix, that is, the final result is obtained

2.1 main factors affecting the content of free formaldehyde

it can be seen from table 1 that factor 1 is independently composed of starch types, factor 2 is mainly linear composed of starch water ratio, oxidation time, oxidation pH, starch urea ratio, factor 3 is mainly linear composed of hydrolysis time, hydrolysis pH and oxidation dose, and factor 4 and factor 5 are independently composed of urea formaldehyde ratio. Free formaldehyde content has a non-zero load on each factor, so five factors have an impact on free formaldehyde content, but factors 1, 3 and 4 have a greater impact on free formaldehyde content, of which factor 3 has the greatest impact. That is, starch type, hydrolysis time, hydrolysis pH, oxidation dose and urea formaldehyde ratio have great influence, and hydrolysis time, hydrolysis pH and oxidation dose have the greatest influence

in other words, urea formaldehyde ratio, which affects the content of free formaldehyde in ordinary urea formaldehyde resin, also has a great influence on the content of free formaldehyde in urea formaldehyde resin modified by oxidized starch, but the greatest influence is the degree of hydrolysis and oxidation of starch. Many papers have discussed the influence of urea formaldehyde ratio, and then close the oil delivery valve. Here, taking the influence of oxidation time as an example, the degree of starch modification is discussed

Figure 1 shows the effect of oxidation time on the content of free formaldehyde when a certain amount of oxidant is used. We can see from the figure that with the extension of oxidation time, the degree of starch oxidation increases, and the content of free formaldehyde in urea formaldehyde resin also increases correspondingly

when starch is oxidized, the hydroxyl group on C6 in some glucose units in its structure is converted into aldehyde group, and the aldehyde group can form hemiacetal and acetal with the hydroxyl group in urea formaldehyde resin under curing agent and heating conditions. Thus, the crosslinking structure with the participation of oxidized starch chain is formed during curing, which effectively prevents the penetration and improves the performance of urea formaldehyde adhesive. As the oxidation degree of starch increases, the aldehyde group is further oxidized to carboxyl group. The reactivity of carboxyl group with amino and imino groups that can reduce the content of free formaldehyde is higher than that of formaldehyde, resulting in the increase of the content of free formaldehyde in the final product

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