SEBS发泡材料介绍—SEBS Foaming Materials

1.SEBS发泡材料介绍

SEBS是利用氢化方式将脂肪族双键饱和化，以期扩大产品应用范围。饱和型热可塑性弹性体SEBS由于软质段为饱和型的烯系结构，耐候性、耐热老化性比SBS更佳，且物性亦较SBS更为强韧，故应用范围更为广泛。 SEBS热塑性弹性体是介于橡胶与树脂之间的一种新型高分子材料，不仅可以取代部分橡胶，还能使塑料得到良好的改性。SEBS具有与传统橡胶相同的弹性、回复性、强韧性与耐候性，及热塑性塑料一样容易加工成型的特性且可以再回收使用等优点。而且它与其它的塑料原料具有极佳的兼容性，且由于SEBS可借由添加扩展油来调整材料软硬度，故可制得硬度范围广泛的发泡制品，发泡成品硬度范围可为5C-60C，比重极低，在0.08-0.3之间。SEBS因具有热可塑的特性，故发泡后的成型品亦可再进行二次定型以制得形状复杂的成品，且SEBS发泡成品可再回收利用。

2. SEBS发泡材料主要特性：

 3. SEBS发泡过程与发泡方法

  发泡过程可以采用许多方法，但是都包括以下几个方面：泡孔形成、泡孔增长，泡孔稳定。发泡剂可以采用机械发泡，化学发泡，物理发泡；

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4. 开孔或闭孔泡沫区别及其形成机理：

    开孔或闭孔泡沫的结构区别：气体以泡孔的形式存在于泡沫体中，泡孔与泡孔互相隔绝的称为闭孔，连通的称为开孔，从而有闭孔泡沫塑料和开孔泡沫塑料之分。泡沫结构的开孔或闭孔是由原材料性能及其加工工艺所决定的。

    开孔或闭孔泡沫形成机理：对于软泡等发泡体系，形成的开孔泡沫的原因可能是几种因素的综合，一般观点认为，大多情况在气泡内产生最大压力时由于凝胶反应形成的泡孔壁膜强度不高，不能承受气体压力升高引起的壁膜的拉伸，气泡壁膜便被拉破，气体从破裂处逸出，形成开孔气泡。

1. Introduction of SEBS Foaming Materials

    Styrene-diene block copolymers were first developed by Shell utilizing anionic block copolymerization of styrene with butadiene (S–B–S) and styrene with isoprene (S–I–S) and were introduced commercially in 1966 as Kraton^®. Phillips Petroleum Co.entered this field in 1968 with radial styrenic block copolymers. In 1972 Shell added the S–EB–S copolymer, where EB is the ethylene-butylene copolymer segment. S–EB–S copolymer is prepared by hydrogenation of the polybutadiene center block thus eliminating the double bonds and improving resistance of the product to oxidative scission and ozone attack . The product was introduced as Kraton G^®.

Polymeric foams or cellular or expanded polymers have played an important role in everyday life. Because of their special characteristics, they became attractive for many industrial and household applications.The most important attributes of polymeric foams are light weight and good thermal insulation property. Other advantages are relatively high strength per unit weight and lower dielectric constant when compared to solid polymers.  Polyethylene, PP, and polystyrene are most common thermoplastic foams, although other base polymers, such as ethylene vinyl acetate (EVA), melt-processable fluoropolymers, and TPEs can be converted into cellular materials.

2. Characteristics of SEBS Foaming Materials

SEBS Foaming Materials offer a variety of advantages over conventional

foaming materials materials, such as the following:

Cost: their volume cost is often lower, because of mixing with oils and the possibility of reusing scrap in the same fashion as with thermoplastics;

Processing: Lower energy consumption due to shorter molding cycles and simpler processing without peculiar smell or frosting, and easy to paint;

Properties: higher anti-slip and compression deformation resistance than EVA foamed sheets. Good hand feeling, and dimensional stability, good tensile elasticity; and comparing with other TPEs，SEBS is with  higher heat resistance, flexibility, and solubility.

3. Foaming Processes and Technology

Many resins can be foamed by a variety of processes. Each method of foam manufacturing involves the following steps:

l         cell initiation

l         cell growth

l         cell stabilization.

Foaming Technology include the below methods:

l         Mechanical Foaming

l         Chemical Foaming

l         Physical Foaming

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4. Difference of structure and mechanism between closed and open cells

Foam cells are bubbles that have been frozen in size and shape after solidification of molten polymer. Such a material can contain two types of cells; closed cells and open cells. In the closed cell foam each cell is an independent closed entity. The cells resemble small glass bubbles that have been dispersed in the polymer. The walls of a closed cell have no holes in them. The cell will contain gas in them if the polymer is impermeable to the gas used for the formation of the cellular structure. The cells in the open cell foam are interconnected, thus unable to hold gas. Liquids and gases can move through the open cell structures, like through common sponges.

Polymeric foams are also classified according to their mechanical properties. If the walls of the cell are stiff under stress and relatively inflexible, the foam is called rigid. If, on the other hand, the cells collapse under stress, the foam is called flexible. Both open cell and closed cell structures can form rigid and flexible foams.

Mechanism of closed cells and open cells：Mainly depend on the materials and processing conditions, such as gas pressure, amount of blowing agents（Source：handbook of thermoplastic elastomers）

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