CÔNG THỨC NHỰA POLYPROPYLENE CẢI THIỆN SỰ CHẬM CHÁY CỦA NGỌN LỬA

Sự sáng chế là cải thiện khả năng kháng cháy công thức nhựa PP có chứa copolymer tác động va đập hoặc nhựa PP biến tính va đập, Tris (tribromoneopentyl) phosphat và tạo ra gốc tự do Cacbon-cacbon. Công thức này phù hợp với tiêu chuẩn chống cháy mức V-0 của 94 UL mà không cần thêm phụ gia trioxide antimon. Ví dụ, 78% của PP copolymer, 17% của Tris (tribromoneopentyl) phosphat (FR 370), và các chất phụ gia, được được tạo hạt trên máy đùn twin-screw để tạo ra một compoound PP kháng va đập và Mức chống cháy đạt V-O theo tiêu chuẩn UL-94.

Ảnh hưởng của chất tương hợp PP-g-MAH trên tính chất của blends PP / ABS

Maleic anhydrit-polypropylene ghép (PP-g-MAH) được đánh giá là một chất tương hợp cho hỗn hợp (blend) PP / ABS) được sử dụng trên máy đùn 2 trục vis. Độ bền kéo, độ bền va đập và độ bền uốn của hỗn hợp đạt được giá trị lớn nhất khi sử dụng hàm lượng PP-g-MA 3%. Phương pháp chụp TEM dùng để xác định hình thái học của hỗn hợp. Phương pháp phân tích TEM chỉ ra rằng kích thước hạt ABS phân tán trên nền PP đạt nhỏ nhất ở 6 micron với hàm lượng chất tượng hợp PP-g-MA 3%. Độ nhớt chảy nhỏ nhất của hỗn hợp 70%PP/30%ABS đạt được với chất tương hợp PP-g-MA 3%.

Source : Lee, Hyung Gon; Sung, Yu-Taek; Lee, Yun Kyun; Kim, Woo Nyon; Yoon, Ho Gyu; Lee, Heon Sang. Department of Chemical and Biological Engineering, Korea University, Seoul, S. Korea. Macromolecular Research (2009), 17(6), 417-423. Publisher: Polymer Society of Korea

Màng co nhiều lớp trên cơ sở nhựa PP

Patent: Sự cải tiến là màng co bọc bên ngoài bao gồm lớp màng lõi và lớp skin (tiếp xúc bề mặt) và một lớp kết dính cho 2 lớp kia. Lớp lõi bao gồm nhựa PP từ 0-30% và 70 đến 100% của random propylene-alpha-olefin copolymer chứa 1 to 10% of C4 to C12 alpha-olefins. Lớp skin có khả năng kháng dung môi.

Thermoforming PLA: How to Do It Right

Polylactic acid (PLA) resins are made from 100% renewable resources such as corn, sugar beets, or sugarcane. This clear thermoplastic is fully compostable and biodegradable but has properties very similar to petroleum-based resins that are typically converted into sheet for thermoforming. Thermoformers who are considering switching to PLA can run it without any major modifications to their equipment or tooling. However, there are some important considerations that need to be addressed before successfully switching from familiar thermoformed materials like oriented PS and PET to PLA.

For one thing, PLA sheet is quite brittle at room temperature and requires some special handling and storage considerations. There is a greater risk of cracking and breaking during shipping compared with OPS or PET, for example. Neither the sheet nor the finished product can be stored at temperatures above 105 F or greater than 50% relative humidity. Exposure to high temperatures or humidity, even for a short period, can cause the material to deform and eventually break down. Sheet and formed products must be transported in cooled trucks and stored in a climate-controlled warehouse.

PLA sheet can be run without any major equipment or tooling modifications for production of food packaging trays for baked goods, fruits, and vegetables.

All of GN Thermoforming Equipment’s testing on PLA has used our contact-heat, cut-in-place thermoforming system. It permits all heating, forming, and cutting of the material to be performed in a single station using compressed air, without the need of a pre-stretch plug or vacuum.

Prior to thermoforming with a new roll of PLA sheet, processors need to establish a starting point for the heating platen temperature. PLA has a low forming temperature compared with petroleum-based plastics. Begin by setting the platen temperature at 140 F, then take a small piece of PLA, hold it on the hot plate, and increase the temperature in increments of 40 F until the material starts to get sticky on the plate. This helps you arrive at a good starting temperature. A preheater is not required for PLA and tends to make the material dry out too quickly without providing any forming benefits.

There tends to be a very narrow temperature window for the heating platen when forming PLA—as little as a couple of degrees in certain blends of the material. If the sheet is too hot, the PLA will not form but “cook” onto the platen. If it’s too cold, the product will not form.

DESIGN AFFECTS MOLD TEMPERATURE
The mold temperature setting depends on the design of the mold. If the tool has bar locks, setting the mold temperature at approximately 104 F to 113 F will provide the best forming results. If there is an undercut on the tool, a mold temperature of 77 F to 86 F will allow the formed product to shrink a bit and eject from the mold easier. For example, a simple packaging tray without special features such as locks or undercuts typically can use a mold temperature anywhere between 77 F and 113 F, depending on the blend of the material.

First-time PLA processors can start by doing single production shots with the heating and forming time at 2 sec, and the other times (heat and form vent, eject delay, eject time, and cut dwell) at 0.2 sec. Adjust times up or down from there until you get a properly formed product, with good detail and acceptable clarity. Then set up a production run and reduce processing times as much as possible. The accompanying table lists process settings for similar products running on a contact-heat, cut-in-place forming machine using OPS, PET, and PLA.

Processors should keep in mind that various PLA blends will behave differently during thermoforming. Different PLA blends from different suppliers may require completely different process parameters. Overall, the cycle times for PLA are quite consistent with those of PET and OPS.

PROCESS SETTINGS FOR OPS, PET & PLA
	0.018- in. PLA	0.020- in. OPS	0.18- in. PET
Mold Temp., F	105	113	113
Heater Platen Temp., F	212	280	257
Heating Time, sec	2.0	2.0	2.5
Heat Vent Time, sec	0.2	0.3	0.2
Forming Time, sec	1.5	1.2	1.2
Form Vent Time, sec	0.2	0.2	0.2
Eject Delay Time, sec	0.2	0.15	0.15
Eject Time, sec	0.2	0.2	0.2
Cut Dwell Time, sec	0.2	0.2	0.2

After the thermoforming process, when the PLA returns to room temperature, the skeletal waste web is very brittle and tends to break easily. This leads to difficulty in transporting the web and requires consistent tension control. Large rollers and a minimal angle when entering the transport rollers will help prevent the web from breaking.

Once PLA has been heated and stretched through the thermoforming process it loses some of its brittleness. Wall thickness in products can be reduced while still retaining product strength, and the formed parts are suitable for automatic stacking upon leaving the thermoformer.

Thermoformed parts made of PLA have excellent clarity, comparable to those formed in OPS and PET. This, combined with the temperature requirements for product storage, make thermoformed PLA suitable mostly for food packaging trays for baked goods, fruits, and vegetables.

Demand for PLA packaging is currently driven by eco-conscious retailers like Wal-Mart. Thermoformers are often less eager to run PLA sheet due to the material’s higher cost and special handling and storage requirements. However, the material does run very well on cut-in-place forming systems, and existing tooling does not require any major modifications to run it. PLA can also be formed on tunnel-heat, plug-assist machinery.

Processing PCR: How It’s Done At a Leading PET Bottle Maker

Many food and beverage companies are either using or thinking about using recycled materials in their packaging. In addition to enhancing brand equity, using post-consumer recycled (PCR) plastics has a number of environmental benefits. Recycling reduces the amount of plastic sent to landfills, and using PCR helps support the recycling infrastructure. Using recycled PET means that less petroleum is needed to make new, virgin resin. Recycled PET also requires less energy to produce and has a lower carbon footprint than virgin PET.

There are several challenges to making bottles with recycled PET, and they increase with the percentage of PCR used. In general, there are no modifications required to machinery or molds, except for the additional equipment needed to store, handle, and blend PCR. However, using PCR often introduces subtle challenges and process considerations. Most often, the quality of the PCR resin will have the most impact on the challenges you’ll face in production.

Probably the most noticeable difference when using PCR is the color. Clear PCR bottles will be somewhat darker and often more yellow than those made of virgin PET. Variation in the sources of PCR is often the culprit.

WHY PCR IS CHALLENGING
For PET bottle processors, the source of almost all PCR is carbonated soft-drink, water, and other beverage bottles. In North America, most soft-drink bottles are collected by one of two methods. Some states have deposit or redemption systems to encourage consumers to recycle their bottles. These return systems usually result in the best quality recovered PET because the bottles are kept separate from other types of plastic and paper, glass, and other potential contaminants. Most bottles collected outside of the deposit or redemption systems are from curbside recycling programs. The PET bottles, and sometimes other containers made from PET, are often mixed with other types of plastic, metal, and glass containers that can contaminate the PET.

The PET resin used for carbonated soft drinks is not identical to the grades typically used for isotonic beverages and most water bottles. The most important difference is the intrinsic viscosity (IV) of the various resins. The IV of a resin increases with the length of its polymer chains, which have an effect on the strength and stretch characteristics of the PET bottle. The ratio of carbonated soft-drink to water bottles will have an impact on the resulting IV in the recycled PET.

In addition to IV, the two most critical quality variables when using PCR are color and contamination. Recycled PET tends to be darker and more yellow than virgin PET. Some of the color comes from reheating, but most comes from contaminants in the PET. Some of the contaminants that affect PCR color are oxygen scavengers, reheat enhancers, or other additives used in the original containers. Contaminants can also be microscopic pieces of foreign material such as other plastics, glass, sand, or metals. These small particles are bound in the plastic and don’t pose a hazard in food containers, but can sometimes be seen as black specs in the resin pellets or in the container. The color and amount of contamination in recycled PET depends on the source of the recycled bottles—deposit or curbside—and also the technology used to sort, wash, and grind the bottles.

PROCESSING PCR
For PET containers, PCR is used in varying amounts from less than 10% to 100%. At ratios below 25%, there are usually only slight differences when using PCR versus 100% virgin. At higher percentages, the use of PCR has a greater impact.

Using PCR requires some additional infrastructure compared with running 100% virgin PET. First, you need a place to hold the PCR. Smaller amounts can be handled in gaylord boxes or Super Sacks. Larger amounts of PCR usually warrant a separate resin silo to store the PCR, which can be delivered in bulk trucks or railcars. Blending equipment, such as a gravimetric blender, is required to mix the PCR with virgin resin at the desired ratio. It’s also possible to purchase PCR preblended with virgin resin, but this limits your options to one ratio. Preblending also increases your risk if the PCR turns out to have unacceptable levels of contamination.

The 50ml PET bottle for McCormick Distilling Co.’s 360 Vodka, developed by Amcor PET Packaging, is the first 100% PCR container in the liquor industry. Method Products Inc. converted three of its U.S. product lines to 100%-PCR PET bottles from Amcor. They are believed to be the first 100%-PCR bottles in the U.S. for household cleaning products.

Probably the most noticeable difference when using PCR instead of 100% virgin PET is the color. When attempting to make clear bottles from PCR, you will notice they will be somewhat darker and often yellower than those made of virgin PET. Because of variation in the sources of the PCR, it can be difficult to maintain a consistent color from batch to batch. Some food and beverage companies overcome these problems by adding colorant. A slight blue tint helps to mask the yellowness and create a more uniform color. Green, amber, or other colors also effectively mask the effects of high percentages of PCR, but they also mean the bottle can’t be recycled again into a clear bottle. If you do your own blending of PCR with virgin resin, you may be able to adjust the ratio of PCR to maintain acceptable color in the final container.

In addition to black specs, larger contaminant particles in PCR can cause problems in injection molding the preform. These contaminants are usually caused by some malfunction in the washing or melt-filtering process, such as a blown filter screen, and are not part of normal day-to-day operation. Otherwise, there is little difference in the injection molding process when producing a preform made of PCR.

Blow molding bottles with PCR usually requires a different set of process parameters than is typical for virgin PET. Because the PCR is darker, it more readily absorbs heat from the blow molding oven lamps, so lamp profiles often need to be adjusted. Small particles of contamination in PCR also can cause pinholes and leaks when blow molding the bottle. As the walls of the bottles are stretched during molding, particles of contamination can cause weaknesses that result in holes in the bottle wall. The number of defects will depend on the amount of contamination in the PCR resin and the design and wall thickness of the preform and final bottle.

YOUNG INFRASTRUCTURE
For packaging materials such as aluminum, glass, and paper, today’s economics and manufacturing processes often support the use of post-consumer recycled materials. With plastics, including PET, the demand for PCR is increasing, but the infrastructure to recycle and preprocess post-consumer plastics is not as well developed.

Using PCR to make new bottles starts with sourcing the right PCR for your application. At the converting plant there may be some infrastructure needed to store, handle, and blend the PCR resin. There generally won’t need to be modifications to the injection and blow molding equipment, but processes will probably need to be developed or at least fine-tuned. Using larger percentages of PCR may require colorants or ongoing management of the supply or of blend ratios to achieve consistent output.

Additives for improving the friction and wear of carbon-fiber-reinforced polyimide

Technical Paper – Polyimide composites should function in sliding contacts under high temperatures, but the interference of carbon fibers with sliding mechanisms is difficult to predict: they often increase the coefficients of friction and act abrasively but show lubricating properties under other conditions. The friction and wear behavior of thermoplastic polyimides reinforced with short carbon fibers and filled with solid internal lubricant (polytetrafluoroethylene) or silicon oil was investigated in this study with a reciprocating cylinder-on-plate tester under 50 N at 0.3 m/s with steel counterfaces that were heated at 23-260°C. We concluded that Teflon additives effectively reduced the coefficients of friction over the entire temperature range, especially under thermally controlled sliding conditions at 120°C, whereas the internal silicon oil increased the coefficients of friction. The wear rates of the fiber-reinforced polyimide significantly decreased with respect to those of the thermoplastic polyimide, whereas additional fillers slightly increased the wear rates. We further analyzed the role of internal additives by considering the deformation and maximum polymer surface temperature during sliding.

Nanocomposites for electronic applications

Technical Paper – Nanocomposites made up of polymer matrices and carbon nanotubes are a class of advanced materials with great application potential in electronics packaging. Nanocomposites with carbon nanotubes as fillers have been designed with the aim of exploiting the high thermal, electrical and mechanical properties characteristic of carbon nanotubes. Heat dissipation in electronic devices requires interface materials with high thermal conductivity. In this article the authors review the current developments and challenges in the application of nanotubes as fillers in polymer matrices. The blending together of nanotubes and polymers result in what are known as nanocomposites. Among the most pressing current issues related to nanocomposite fabrication are (i) dispersion of carbon nanotubes in the polymer host, (ii) carbon nanotube-polymer interaction and the nature of the interface, and (iii) alignment of carbon nanotubes in a polymer matrix. These issues are believed to be directly related to the electrical and thermal performance of nanocomposites. The recent progress in the fabrication of nanocomposites with carbon nanotubes as fillers and their potential application in electronics packaging as thermal interface materials is also reported.

Source : Jones, Wayne E., Jr.; Chiguma, Jasper; Johnson, Edwin; Pachamuthu, Ashok; Santos, Daryl. Chemistry Department, Binghamton University, Vestal Parkway East, USA. Materials (2010), 3 1478-1496. Publisher: Molecular Diversity Preservation International