All kinds of raw materials used in the production of melt spun nonwovens are "thermoplastic" plastics. Thermoplasticity refers to the characteristic that plastic can be softened by repeated heating within a specific temperature range and hardened after cooling. All kinds of raw materials used in spunbonded and melt blown nonwoven production processes are solid at room temperature, sometimes referred to as "chips" or "resins". As different raw materials are used, the characteristics of the products will be different, the production process will be different, and the performance and configuration of the equipment will be different, which will have a significant impact on the use, market, economic benefits of the products and the price of the production line. Therefore, raw materials are the first prerequisite for determining the performance indicators of the production line.
Raw materials used in the production process of melt spun nonwovens mainly include polypropylene (PP), polyethylene (PE), polyester (PET), polyamide (PA), polyurethane (PU), polylactic acid (PLA), etc. Among them, polypropylene (PP) is the most commonly used, most used and most widely used raw material. Here are some introductions on the characteristics of polypropylene (PP) and the requirements of the spinning and melting production line for PP chip raw materials.

Polypropylene (PP)

Polypropylene is the most commonly used raw material at present, and also the most important polymer fiber raw material. In China, nearly 94% of spunbonded fabric and melt blown fabric raw materials are polypropylene. In the fields of medical treatment, health care and health care, polypropylene nonwovens account for 50% of the total nonwovens.

Characteristics of polypropylene (PP)

Polypropylene fiber has very low density (0.91g/cm3); Low water content (<0.1%,); Good chemical resistance (acid, alkali, solvent); Mould proof, anti-corrosion, moth proof and antibacterial; Good heat insulation, heat preservation and insulation performance; High rigidity and good tensile strength (4.5~7.5cN/dtex); Good fatigue resistance and wear resistance; Temperature resistance: 120 ℃, melting point: 165 ℃; Easy to be recycled. These characteristics make polypropylene fiber different from other synthetic fibers in two aspects: first, its moisture absorption is very low, which makes polypropylene fiber have excellent stain resistance and almost the same dry and wet properties; Second, it has the smallest density of all fibers, which makes it have good coverage under the same weight conditions.
As the thermal conductivity of polypropylene is the lowest among all fibers, its thermal insulation effect is better than wool, and its fiber not only has low density, but also has a large coverage area, which can be used as home and vehicle interior filler, thermal insulation floc materials, sound absorption, thermal insulation materials, etc.
On the other hand, polypropylene does not react with general chemical reagents and has strong chemical resistance. Polypropylene nonwovens can be used to manufacture geotextiles, lead battery separators, filter materials, etc. Because there is no active group in the main chain of polypropylene fine denier fiber, the material itself is not easy to be eroded by bacteria and mold, and it has no irritation, non-toxic, etc. in contact with human skin, and has good health performance, so it can be widely used in the medical and health field. In addition, the lipophilic chain structure of polypropylene and the internal capillary structure formed due to the crystal transformation during fiber post stretching make its products have strong oil absorption and can be used to produce oil absorption felt materials.

Requirements of spinning and melting production line for PP chip raw materials

In the process of polypropylene spinning, different grades of PP chips are often used, and their spinnability will be greatly different, such as the length of spinneret component service life, the yield of broken wires, and the uniformity of fibers. However, to be used as spinning grade polypropylene (PP) chip raw material for spinning and melting production, the following conditions must be met:
(1) Melt index (MFI):
25 ～ 40g/10min for spunbonded method,
400~1500g/10min for melt blowing method.
(2) Molecular weight distribution width (Mw/Mn): ＜ 4~5.
(3) Melting point: 164~170 ℃ (the melting point of pure isotactic polypropylene is 176 ℃).
(4) Density: 0.91 g/cm3;
(5) Isotacticity: ≥ 96%.
(6) Ash content: ≤ 0.025% (weight).
(7) Moisture content: ≤ 0.05% (weight).
(8) The appearance is smooth, the particle size is uniform, and there is no coalescence.
The raw materials used in the production line are related to the market positioning of the product and the use of the product. In order to reduce production costs, inferior raw materials can be selected for the production of low-end products due to low requirements for raw materials; High end products have high requirements for the performance of raw materials, so they need to choose high-quality raw materials with high prices. The price of PP chips is directly related to the size of its MFI. Generally, the larger the MFI, the higher the price. Therefore, it is necessary to comprehensively consider the production process, equipment characteristics, product use, product sales price, production cost and other factors to select the raw materials to be used.