Influence of carbon additives on the structure and properties of polypropylene

ABSTRACT

In this work, the impact strength of samples of the original PP and the studied mixtures of polypropylene and carbon additives (PP / UD) and the elongation at break of the samples of PP and PP / UD mixtures under tension at a speed of 50 mm / min were determined. Shown are the values of the MFI and the mechanical indices for tensile samples of the initial PP and the studied PP / UD mixtures.

АННОТАЦИЯ

В работе определены ударная вязкость образцов исходного ПП и исследуемых смесей полипропилен и углеродных добавок (ПП/УД) и относительное удлинение при разрыве образцов ПП и смесей ПП/УД при растяжении со скоростью 50 мм/мин. Показаны значения ПТР и механические показатели при растяжении образцов исходного ПП и исследуемых смесей ПП/УД.

Keywords: polymer nanocomposites, polypropylene, tar product, carbon black, impact strength, strength

Ключевые слова: полимерные нанокомпозиты, полипропилен, тар продукт, сажа, ударная вязкость, прочность

As you know, PP (polypropylene) does not meet the requirements for impact resistance and frost resistance for use in many cases. Therefore, in practice, PP is usually used in the form of composites with modifiers of various nature. The addition of mineral fillers leads to an increase in hardness and heat resistance, but the impact resistance often decreases. Joint composition of PP filler when using a suitable compounding method at certain ratios between the components, makes it possible to obtain composites with an optimal balance of physical and mechanical properties [1].

Carbon materials have long established themselves as fillers in the production of composite materials based on polymers. [1,2,5]. So, the use of soot and carbon black allows not only to reduce the cost of products based on polymers, but also to give them electrical conductivity. Although the electrical conductivity of the carbon black-filled compositions occurs at sufficiently high degrees of filling, containing 10-15%, the ability to impart antistatic properties to the composition is an advantage. As you know, the addition of ordinary inert fillers almost always negatively affects the physicomechanical properties of the composition, which fully applies to the filling of polymers with carbon black. Thus, filling polypropylene without prior orientation with carbon black leads to an increase in rigidity, a decrease in impact strength, and a decrease in elongation at break. However, the addition of carbon black in an amount greater than 10 wt. % in polypropylene, leads to a sharp decrease in the strength of the composite. In contrast, the heat resistance of polypropylene (PP) increases as the degree of carbon black (CB) filling increases. [1-5]

Two types of carbon additives were obtained based on local raw materials. One of them is graphene oxide, obtained from graphite, the second is carbon black or technical carbon based on product containers, produced by “UzKorGaz Chemical” LLC JV in Uzbekistan. 

 In fig. 1 shows the results of determining with method of the Charpy impact strength on notched specimens for PP / CA (carbon additives) mixtures at room temperature in comparison with the original PP. It can be seen that with the introduction of 0.01-0.1% by weight of carbon additives (CA) in PP, the impact strength at room temperature significantly increases.

Figure 1. Impact toughness of samples of initial PP and studied PP / CA mixtures

The introduction of 0.01-0.1% mass of UF into PP causes a slight increase in the elongation at break, determined at room temperature and a tensile rate of 50 mm / min (Fig. 2 and Table 1). In this case, the elongation at the yield point also noticeably increases (Table 1). In cases of stretching at slower speeds (10 and 20 mm / min), samples of both the original PP and PP / CA mixtures are capable of deforming to high values. This indicates the dependence of the deformation mechanism of the PP matrix on the stretching rate.

Figure 2. Relative elongation at break of PP samples and PP / CA mixtures under tension at a speed of 50 mm / min.

However, when UF is added to PP, the modulus of elasticity (stiffness) and tensile yield point decrease (Table 1), which is not a well-known tendency when PP is modified by CA.

Table 1.

 Values of MFR and mechanical indices under tension of samples of the initial PP and the studied PP / CA mixtures

For comparison with the PP / GO, PP / Carbon black mixtures were prepared. Used PP and carbon black have lower MFI values than PP and GO, respectively.

For the PP / CA mixtures under study, a decrease in the molecular weight of the PP matrix leads to a noticeable decrease in the impact toughness at room temperature, as well as to a decrease in the elongation at break, but has little effect on the elastic modulus and tensile yield strength.

Thus, the introduction of CA into polypropylene improves the physicomechanical properties of the composition.

References:

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