Temperature impact

Some cast (unoriented) polypropylene film is produced. Its clarity and heat sealabiUty make it ideal for textile packaging and overwrap. The use of copolymers with ethylene improves low temperature impact, which is the primary problem with unoriented PP film. Orientation improves the clarity and stiffness of polypropylene film, and dramatically increases low temperature impact strength. BOPP film, however, is not readily heat-sealed and so is coextmded or coated with resins with lower melting points than the polypropylene shrinkage temperature. These layers may also provide improved barrier properties. 

Polypropylene polymers are typically modified with ethylene to obtain desirable properties for specific applications. Specifically, ethylene—propylene mbbers are introduced as a discrete phase in heterophasic copolymers to improve toughness and low temperature impact resistance (see Elastomers, ETHYLENE-PROPYLENE rubber). This is done by sequential polymerisation of homopolymer polypropylene and ethylene—propylene mbber in a multistage reactor process or by the extmsion compounding of ethylene—propylene mbber with a homopolymer. Addition of high density polyethylene, by polymerisation or compounding, is sometimes used to reduce stress whitening. In all cases, a superior balance of properties is obtained when the sise of the discrete mbber phase is approximately one micrometer. Examples of these polymers and their properties are shown in Table 2. Mineral fillers, such as talc or calcium carbonate, can be added to polypropylene to increase stiffness and high temperature properties, as shown in Table 3. 

The low temperature impact strength of stmctural steels was found to be significantly improved with the additions of 0.022—0.008% Te. The low (—40° C) temperature impact strength of a steel annealed at blue brittie temperature of 350°C did not show any embrittlement effect with the addition of. 002% Te (76). 

In these mbber-modified polystyrene polymers, the mbbers should have low T, large particle sizes (0.5—5 J.m), graftable and cross-linkable sites, and should be compatible with styrene monomer (93). Polybutadiene, with a T of —SS C, meets all of these requirements and is used most frequently. These mbber-modified systems exhibit excellent low temperature impact strength, a required attribute for use in refrigerators. 

VLDPEs, with their very good low-temperature impact properties, are of interest in frozen food packaging. By 1998 the market for UHMWPE materials was estimated at 65 000t.p.a. of which Ticona had about half the market share. 

This daia indicates that the random copolymer has greater transparency but inferior low temperature impact strength. 

The hydroxyl content of commercial material is kept low but it is to be observed that this has an effect on the water absorption. Variation in the residual acetate content has a significant effect on heat distortion temperature, impact strength and water absorption. The incorporation of plasticisers has the usual influence on mechanical and thermal properties. 

Hybrids of block copolymer rubbers and acrylics have also been used to increase the low-temperature impact resistance of the adhesive used for body-side molding attachment [127]. To further enhance performance, a new type of hybrid adhesive has been developed, which combines an adhesive polymer, like an... 

The particle size of the dispersed phase depends upon the viscosity of the elastomer-monomer solution. Preferably the molecular weight of the polybutadiene elastomer should be around 2 x 10 and should have reasonable branching to reduce cold flow. Furthermore, the microstructure of the elastomer provides an important contribution toward the low-temperature impact behavior of the final product. It should also be emphasized that the use of EPDM rubber [136] or acrylate rubber [137] may provide improved weatherability. It has been observed that with an increase in agitator speed the mean diameter of the dispersed phase (D) decreases, which subsequently levels out at high shear [138-141]. However, reagglomeration may occur in the case of bulk... 

Testing different impact properties at various temperatures produces a plot that looks very much like an elongation vs. temperature curve. As temperatures drop significantly below the ambient temperatures, most TPs lose much of their room-temperature impact strength. A few, however, are on the... 

Table 5-2 Room temperature impact resistance data for several plastics...

Polypropylene/ethylene-propylene-diene Low-temperature impact resistance and flexibility... 

Automotive Spoilers Seat backs Bumpers Underhood tubing Low temperature, impact, cost Heat distortion, strength/weight Low temperature, impact dimensional stability Chemical resistance, heat... 

Leisure Flotation devices Marine buoys Sailboards Toys Canoes/kayaks Low temperature, impact strength cost, weatherability Low temperature, impact strength cost, weatherability Low temperature, impact strength cost, weatherability Low temperature, impact strength cost, weatherability Low temperature, impact strength cost, weatherability... 

Industrial Tool boxes, ice chests Trash containers, drums Hot-water tanks Low temperature, impact strength, cost Low temperature, impact strength, cost Low temperature, impact strength, cost... 

Polycarbonate is an extremely versatile polymer with a wide range of applications. Its stiffness, high heat distortion temperature, impact resistance, and clarity make it a favorite choice for durable goods tvith demanding application requirements. Its high modulus allows it to be used in many automotive, medical and domestic applications. 

Measured surface areas (11-point BET analyses) for pure phases such as ferrihydrite, goethite and hematite are in the range as proposed by Cornell Schwertmann (2003) (Table 1). Preliminary XRD analyses showed that temperature impacts the kinetics of phase transformation of ferrihydrite. Data indicated that after seven days, the rate of transformation from ferrihydrite to more crystalline forms, if it was occurring, was too slow to be measured at 25°C (Fig. 1). In contrast to the 25°C experiment, significant, transformations were observed at 50 (Fig. 2) and 75°C (Fig. 3) after 24... 

Other aspects concern the complex temperature impacts of the in-sewer processes. Sewer processes, microbial as well as physicochemical like reaeration, are temperature dependent. The different processes interact, and the overall temperature dependency of a specific phenomenon may therefore not... 

The authors found that the best rates were observed over the catalysts with a mild calcination treatment (200-250 °C range). The calcination temperature impacted the... 

Better low-temperature behaviour regulations tend towards an increase in low-temperature impact resistances and a more ductile behaviour. 

Low-temperature impact tests cooled samples are subjected to a conventional impact test. Generally, the temperatures most often used are -20°C, -30°C or -40°C. 

PS Sensitivity to UV, low temperatures, impact (apart from butadiene-modified grades), solvents, heat readily flammable with dripping and dense black smoke sometimes difficult machining. 

Ruotsalainen AL, Rytoviita M-M, Mycorrhiza does not alter low temperature impact on Gnaphalium norvegicum, Oecologia 140 226—233, 2004. 

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