Development of High Expansion Ratio Granular Styrofoam Based on Honeycomb Filling

Abstract: This article reports the development and properties of a high-inflation ratio particulate styrofoam for high honeycomb cores. The adhesive is made of polysulfone modified epoxy resin as the main material, dicyandiamide as the curing agent, azobisisobutyronitrile as the foaming agent, and aluminum powder as the filler, which has high adhesive strength and good The durability. The glue was used to fill the components of the peak core and showed a good weight saving effect. The adhesive structural parts subjected to the vibration, static, impact and other environmental assessment tests were all successful.

Key words: medium temperature curing, honeycomb filling, high expansion ratio, styrofoam

Foreword

With the rapid development of China's aerospace and aviation industries, the honeycomb sandwich structure has become the main structural form of satellites, vehicles, and aircraft. The size of the honeycomb sandwich structure is sometimes very high. In the past, the core height of the bee was only 20-30mm, and now it is sometimes 70mm high. As the height of the bee core increases, the filling difficulty of the bee core gradually increases. For this reason, the styrofoam filled with the high core requires a higher expansion ratio (>4) to reduce the structural weight. The high expansion ratio ribbon styrofoam is suitable for the bee core height 15-30mm, and can be pressed into the bee grid on the press; and when the bee core height is more than 50mm, due to the large number of layers of the adhesive tape, a displacement occurs during the pressing and cannot be Controlling the size of the filling space can also cause partial lack of glue and affect reinforcing performance. For this reason, it is necessary to fill the high-rise core structure with a high expansion ratio of powdered styrofoam. However, when the high expansion ratio is filled with the powdery styrofoam, since the expansion is too large, not only the size of the filling space cannot be controlled, but also the bulge is easily generated. If partial filling is used, due to the large construction area and lots of beehive holes, it is not easy to grasp the amount of addition and the degree of uniformity, and thus the effect of reinforcement. For this purpose, we have developed a granular high-expansion ratio styrofoam with a certain external dimensions to meet the needs of the high-bee core sandwich structure. Because it has a certain shape and size when filled, there is still a certain amount of free space. To ensure that the high expansion ratio of styrofoam when foaming, does not bulge and can strictly control the size of the space that should be filled.

It is difficult to develop medium temperature curing granular styrofoam because the softening temperature of the rubber matrix is ​​closer to the curing temperature (120-130°C) and the softening point range of the matrix is ​​more difficult to control. If the softening point is slightly higher, in the softened or viscous state, mixed with aluminum powder, curing agent, foaming agent, part of the foaming agent has been decomposed, resulting in unstable expansion ratio, uneven surface of the workpiece, but also due to plastic When the matrix is ​​softened, the medium-temperature curing curing agent and accelerator have already started the curing reaction, so that the viscosity of the system rapidly increases and it is difficult to foam; if the softening point is low, the granular styrofoam will be blocked during transportation and storage. Not available. Through experiments, we have developed a high-expansion ratio particle styrofoam with a certain external dimensions.

1 Test section

1.1 Raw materials

E—51 Epoxy Resin Industrial Products Yueyang Resin Factory Polysulfone Industrial Products Dalian Plastics Second Factory Aluminum Powder Industrial Products Northeast Light Alloy Factory Azobisisobutyronitrile Chemical Pure Shanghai Reagent No.4 Factory

1.2 test steps

(1) React epoxy resin with toughening material to toughen epoxy resin

(2) The epoxy resin is reacted with a certain amount of curing agent under certain conditions (temperature and time) to obtain a B-state resin

(3) Add the above B-state resin and a certain amount of curing agent, accelerator, aluminum powder, foaming agent, and other auxiliary materials to the resin in the mixer

(4) Sheets with a thickness of 1 to 2 mm are prepared on a tablet maker and frozen in a refrigerator

(5) Crushing and sifting step by step on a slicer mill to produce a finished product with a diameter of 2 to 4 mm, returning a slice of less than 2 mm and more than 4 mm and smashing

2 Results and Discussion

2.1 Screening of Curing Agents

Select and synthesize suitable curing agent A, mix it with epoxy resin and its toughening agent, and then fully pre-react at 160-180°C × 2h, (incomplete reaction will affect the softening point and stability of the product). According to different amounts of A added, a series of B-state resins with different softening points were prepared and the suitable softening point range was selected. Softening point is too low, easy to stick during transportation and storage, and can not maintain the shape; softening point is too high, near the temperature of the medium temperature curing (120 ~ 130 °C), styrofoam does not flow at this temperature is difficult to expand, can not reach High expansion ratio.

2.2 Screening and synthesis of moderately cured accelerator system

The system should have good latent performance (no curing reaction at B-state resin softening temperature). Dicyandiamide is a common curing agent for epoxy resin adhesives. It is non-toxic and non-toxic. However, due to its high thermal decomposition temperature, it is necessary to cure the epoxy resin at 150° C. or higher, and it must be modified at 120 to 130° C. for curing. The medium temperature curing accelerator is the core of the medium temperature curing structural adhesive, and it has an important influence on the durability and other properties of the structural adhesive. According to reports in the literature, most of the medium-temperature adhesives in foreign countries use various types of urea. Generally, they are mostly N-chlorophenyl-N,N-dimethylurea (chlorourea) or 4,4-dichlorophenyl-N,N. - Dimethyl urea is used as an accelerator to increase the curing activity of dicyandiamide, the curing temperature is reduced from 170 to 180°C to 120 to 130°C, and has good latent property, but the cured product has poor resistance to moist heat aging. The use of 2-ethyl-4-methylimidazole for the promotion of dicyandiamide has improved moisture and heat resistance, but its latent property is extremely poor. In order to achieve the high activity and good latent properties and durability of foreign adhesives, we have developed a medium-temperature cure. Accelerator K is used in adhesives.

(to be continued)