阅读说明：本技术 一种芳族砜聚合物、玻纤增强复合材料及其制备方法 (Aromatic sulfone polymer, glass fiber reinforced composite material and preparation method thereof ) 是由 高红军 王道波 张登 黄险波 叶南飚 孙学科 陈锐斌 杨硕 姜苏俊 曹民 于 2020-12-23 设计创作，主要内容包括：本发明涉及一种芳族砜聚合物、玻纤增强复合材料及其制备方法。该芳族砜聚合物的酚端基含量为80～160mol/t。本发明通过研究发现,芳族砜聚合物的酚端基含量对芳族砜类纤维复合材料的力学性能有较大影响,通过调控酚端基含量,芳族砜聚合物与玻璃纤维有较强的相互作用力(如与纤维表面羟基的氢键作用),得到的玻纤增强复合材料的拉伸强度和弯曲强度显著提高,力学性能明显改善。(The invention relates to an aromatic sulfone polymer, a glass fiber reinforced composite material and a preparation method thereof. The aromatic sulfone polymer has a phenolic terminal group content of 80 to 160 mol/t. According to the invention, researches show that the phenolic end group content of the aromatic sulfone polymer has a great influence on the mechanical properties of the aromatic sulfone fiber composite material, and the aromatic sulfone polymer and the glass fiber have strong interaction force (such as hydrogen bond interaction with the hydroxyl on the surface of the fiber) by regulating the phenolic end group content, so that the tensile strength and the bending strength of the obtained glass fiber reinforced composite material are obviously improved, and the mechanical properties are obviously improved.)

1. An aromatic sulfone polymer characterized in that the aromatic sulfone polymer has a phenolic terminal group content of 80 to 160 mol/t.

2. The aromatic sulfone polymer of claim 1, wherein the aromatic sulfone polymer has a phenolic terminal group content of 115 to 135 mol/t.

3. The aromatic sulfone polymer of claim 1, wherein the aromatic sulfone polymer is one or more of polyphenylsulfone, polyethersulfone, polysulfone, or polyetherethersulfone.

4. The aromatic sulfone polymer of claim 1, wherein the phenolic end groups comprise a phenolic hydroxyl end group and a phenolate end group.

5. A process for producing an aromatic sulfone polymer as described in claim 1 to 4, which comprises the steps of:

s1, salt forming reaction: mixing a phenol monomer, a sulfone monomer, a salt forming agent, an entrainer and a solvent, and carrying out a salt forming reaction at 180-220 ℃;

s2, polymerization: and heating the system subjected to the salt forming reaction of S1 to 230-240 ℃ for polymerization reaction, adding a monohalogenated compound for continuous reaction until the polymerization reaction is finished, and performing post-treatment to obtain the aromatic sulfone polymer.

6. The method as claimed in claim 5, wherein the phenolic monomer in S1 is 4, 4-

One or more of dihydroxy diphenyl sulfone, biphenol or 2, 2' -bis (4-hydroxyphenyl) propane.

The sulfone monomer is one or more of 4,4 '-dichlorodiphenyl sulfone, 4' -difluorodiphenyl sulfone or bis- (4-chlorobenzenesulfonyl) biphenyl;

the salt forming agent is one or two of sodium carbonate or potassium carbonate;

the entrainer is one or more of toluene, xylene or trimethylbenzene;

the solvent is one or more of sulfolane, N-methyl pyrrolidone and N, N' -dimethyl acetamide.

7. The method according to claim 5, wherein the monohalogenated compound in S2 is one or more selected from methyl chloride, ethyl chloride, 4-fluoro diphenyl sulfone, 4-chloro diphenyl sulfone and 4-bromo diphenyl sulfone.

8. The method according to claim 5, wherein the molar ratio of the monohalogenated compound to the phenol-containing monomer in S2 is 0.09-0.15: 1.

9. The glass fiber reinforced composite material is characterized by comprising the following components in parts by weight:

59 to 95 parts of the aromatic sulfone polymer described in any one of claims 1 to 4;

5-40 parts of glass fiber;

0.01-0.5 part of antioxidant.

10. The method for preparing the glass fiber reinforced composite material of claim 9, which is characterized by comprising the following steps:

and mixing the aromatic sulfone polymer, the glass fiber and the antioxidant, and performing melt extrusion to obtain the glass fiber reinforced composite material.

Technical Field

The invention belongs to the technical field of high molecular materials, and particularly relates to an aromatic sulfone polymer, a glass fiber reinforced composite material and a preparation method thereof.

Background

The aromatic sulfone polymer belongs to special engineering plastics with high temperature resistance and excellent mechanical property, has excellent characteristics of chemical corrosion resistance, excellent electrical property, stable size and the like, and is widely applied to the fields of aerospace, medical treatment, food and the like. In order to further improve the mechanical properties of the material and meet the requirements of the fields of airplanes, automobiles, machinery and the like on the high-strength high-modulus material, the development and optimization of the preparation technology of the aromatic sulfone fiber reinforced composite material become research hotspots. However, because the fiber surface is smooth, inert and low in surface energy, the wettability and cohesiveness of the fiber surface are low, and the fiber is difficult to be efficiently compounded with the traditional thermoplastic high polymer material to form a high-strength and high-modulus fiber composite material. Meanwhile, due to the high processing temperature (such as PPSU, PPSU processing temperature 350 ℃), the aromatic sulfone polymer can cause the active groups obtained by the treatment of the fiber to be decomposed at high temperature and be greatly lost. Researchers in the field generally improve the interaction with a resin substrate (CN102965928A) by screening fibers containing polyhydroxy groups or adding a coupling agent and the like, so as to improve the mechanical property, but because the interaction between the fibers and the resin substrate is weaker due to less action points caused by more functional group loss at relatively higher processing temperature, a fiber reinforced composite material with good wettability and excellent surface adhesion cannot be obtained, and the requirements of high strength and high modulus cannot be met. Meanwhile, on the premise of not changing the main chain structure of the aromatic sulfone resin and not adding additives for improving the cohesiveness, such as a coupling agent and the like, the research on improving the interaction between the resin and the fiber and further obtaining the high-strength and high-modulus aromatic sulfone fiber composite material is rarely reported.

Disclosure of Invention

The invention aims to overcome the defect of the prior high-strength high-modulus aromatic sulfone fiber composite material and provide an aromatic sulfone polymer. According to the invention, researches show that the phenolic end group content of the aromatic sulfone polymer has a great influence on the mechanical properties of the aromatic sulfone fiber composite material, and the aromatic sulfone polymer and the glass fiber have strong interaction force (such as hydrogen bond interaction with the hydroxyl on the surface of the fiber) by regulating the phenolic end group content, so that the tensile strength and the bending strength of the obtained glass fiber reinforced composite material are obviously improved, and the mechanical properties are obviously improved.

It is another object of the present invention to provide a method for preparing the above aromatic sulfone polymer.

The invention also aims to provide the glass fiber reinforced composite material.

The invention also aims to provide a preparation method of the glass fiber reinforced composite material.

In order to achieve the purpose, the invention adopts the following technical scheme:

an aromatic sulfone polymer having a phenolic terminal group content of 80 to 160 mol/t.

The inventor of the present invention has repeatedly found that the phenolic terminal group content of the aromatic sulfone polymer has a large influence on the mechanical properties of the composite material of the aromatic sulfone polymer and the glass fiber. Specifically, under the specific content of the phenolic terminal group, the aromatic sulfone polymer can have stronger interaction force with the fiber (such as hydrogen bond interaction with hydroxyl on the surface of the fiber), so that the polymer in the composite material after blending and extrusion has stronger interaction with the fiber, the tensile strength and the bending strength are obviously improved, and the mechanical property is obviously improved. If the content of the phenolic end group is too low, the aromatic sulfone polymer can have stronger interaction force with the fiber too weak, and the improvement effect is poor; if the content of the phenolic terminal group is too high, the resin has poor thermal stability, can be degraded in the high-temperature processing process, and has reduced molecular weight, so that the mechanical property is reduced.

Preferably, the aromatic sulfone polymer has a phenolic end group content of 115 to 135 mol/t.

The existing conventional aromatic sulfone polymer types can be subjected to the regulation of the content of the phenolic terminal group.

Preferably, the aromatic sulfone polymer is one or more of polyphenylsulfone, polyethersulfone, polysulfone or polyether ether sulfone.

Preferably, the phenolic end groups comprise a phenolic hydroxyl end group and a phenolate end group.

The preparation method of the aromatic sulfone polymer comprises the following steps:

s1, salt forming reaction: mixing a phenol-containing monomer, a sulfone monomer, a salt forming agent, an entrainer and a solvent, and carrying out a salt forming reaction at 180-220 ℃;

s2, polymerization: and heating the system subjected to the salt forming reaction of S1 to 230-240 ℃ for polymerization reaction, adding a monohalogenated compound for continuous reaction until the polymerization reaction is finished, and performing post-treatment to obtain the aromatic sulfone polymer.

Aromatic sulfone polymers are generally polymerized by a phenol-containing monomer (phenol-containing end group) and a sulfone monomer (chlorine-containing end group) in excess, the end group being predominantly a chlorine end group at the end of the polymerization reaction. However, since it is difficult to completely and sufficiently conduct the polymerization reaction, a certain amount of phenol terminal groups still remain. According to the invention, the monohalogenated compound is added in the synthesis process of the aromatic sulfone polymer to realize effective regulation and control of the phenolic end group of the polymer, specifically, the monohalogenated compound can react with the unreacted phenolic end group, so that the content of the phenolic end group is reduced, and the regulation and control of the content of the phenolic end group can be realized by regulating and controlling the dosage of the monohalogenated compound.

Monomers, salt formers, azeotroping agents, solvents, and the like, which are conventionally used in the art to synthesize aromatic sulfone polymers, can be used in the present invention, also in conventional amounts.

Preferably, the phenolic monomer in S1 is one or more of 4,4 '-dihydroxydiphenyl sulfone, biphenol, and 2, 2' -bis (4-hydroxyphenyl) propane.

Preferably, the sulfone monomer is one or more of 4,4 '-dichlorodiphenyl sulfone, 4' -difluorodiphenyl sulfone or bis- (4-chlorobenzenesulfonyl) biphenyl.

Preferably, the salt forming agent is one or both of sodium carbonate and potassium carbonate.

Preferably, the entrainer is one or more of toluene, xylene or trimethylbenzene.

Preferably, the solvent is one or more of sulfolane, N-methyl pyrrolidone or N, N' -dimethyl acetamide.

Preferably, the molar ratio of the sulfone monomer to the phenol monomer is 1.01-1.05: 1.

Preferably, the molar ratio of the salt forming agent to the phenolic monomer is 1.01-1.20: 1.

Preferably, the mass molar ratio of the entrainer to the phenolic monomer is 20-200 g/mol.

Preferably, the monohalogenated compound in S2 is one or more of methyl chloride, ethyl chloride, 4-fluoro diphenyl sulfone, 4-chloro diphenyl sulfone or 4-bromo diphenyl sulfone.

Preferably, the molar ratio of the monohalogenated compound to the phenolic monomer in S2 is 0.09-0.15: 1.

Better regulation and control of the content of the phenol end group can be realized under the dosage range.

Specifically, the preparation method of the aromatic sulfone polymer comprises the following steps:

(1) salt forming reaction: quantitatively adding a solvent (such as sulfolane, N-methyl pyrrolidone, N' -dimethylacetamide and the like), a reaction monomer (wherein the mole number of sulfone monomers is slightly higher than that of the sulfone monomers), a salt forming agent (such as sodium carbonate, potassium carbonate and the like), and an entrainer (such as toluene, xylene, trimethylbenzene and the like) into a reaction kettle, reacting at 180-220 ℃ by adopting a solution polycondensation method, azeotropically and continuously removing reaction water by the entrainer in the reaction process until no water is removed, finishing a salt forming reaction, and distilling out the entrainer;

(2) polymerization reaction: after the entrainer is evaporated, further heating, stabilizing the reaction system to 230-240 ℃, keeping for 1-2 h, adding the monohalogenated compound, and continuing to react for 1-2 h until the polymerization reaction is finished;

(3) and (3) post-polymerization treatment: stopping stirring and heating, precipitating the polymer material in water to form strips, crushing by a crusher to obtain powdery material, boiling with deionized water, centrifugally filtering, repeating for several times until the byproduct salt is removed, and removing water from the purified polymer under vacuum drying to obtain the aromatic sulfone polymer.

The use of the above aromatic sulfone polymers in the preparation of aromatic sulfone compositions is also within the scope of the present invention.

The glass fiber reinforced composite material comprises the following components in parts by weight:

59 to 95 parts of the aromatic sulfone polymer;

5-40 parts of glass fiber;

0.01-0.5 part of antioxidant.

Both glass fibers and antioxidants conventional in the art can be used in the present invention.

Preferably, the antioxidant is one or more of hindered phenol antioxidant, hindered amine antioxidant, phosphite antioxidant, thioester antioxidant, thiol antioxidant or metal deactivator.

Other functional additives commonly used in the art, for example, inorganic pigments (salts such as metal oxides, sulfides, sulfates, chromates, molybdates, and the like, carbon black, and the like, in an amount of 0.01 to 10 parts by weight), organic pigments (azo pigments, phthalocyanine pigments, heterocyclic pigments, lake pigments, dyes, fluorescent brighteners, fluorescent pigments, and the like, in an amount of 0.01 to 2 parts by weight), lubricants (fatty acid amides, hydrocarbons, fatty acids, esters, alcohols, metallic soaps, complex lubricants, and the like, in an amount of 0.01 to 0.5 part by weight), light stabilizers (light-shielding agents, ultraviolet absorbers, glass fiber quenchers, radical scavengers, hydroperoxide decomposers, and the like, in an amount of 0.01 to 0.5 part by weight), antistatic agents (alkyl sulfate type anionic antistatic agents, quaternary ammonium salt type cationic antistatic agents, and the like, in an amount of 0.01 to 2 parts by weight), and the like may be added to the reinforced composite material of the present invention, to improve the corresponding performance.

The preparation method of the glass fiber reinforced composite material comprises the following steps: and mixing the aromatic sulfone polymer, the glass fiber and the antioxidant, and performing melt extrusion to obtain the glass fiber reinforced composite material.

The application of the glass fiber reinforced composite material in preparing airplanes, automobiles or mechanical products is also within the protection scope of the invention.

Compared with the prior art, the invention has the following beneficial effects:

according to the invention, the aromatic sulfone polymer obtained by regulating the content of the phenolic terminal group of the aromatic sulfone polymer has stronger interaction force with the glass fiber, so that the glass fiber reinforced composite material is endowed with excellent tensile strength and bending strength, and the mechanical property is obviously improved.

Detailed Description

The invention is further illustrated by the following examples. These examples are intended to illustrate the invention and are not intended to limit the scope of the invention. Experimental procedures without specific conditions noted in the examples below, generally according to conditions conventional in the art or as suggested by the manufacturer; the raw materials, reagents and the like used are, unless otherwise specified, those commercially available from the conventional markets and the like. Any insubstantial changes and substitutions made by those skilled in the art based on the present invention are intended to be covered by the claims.

Some of the reagents selected in the examples and comparative examples of the present invention are described below:

sulfolane: solvent, Liaoyang Guanghua chemical industry Co., Ltd., purity > 99.8%;

4, 4' -dichlorodiphenyl sulfone: the reaction monomer, Taiwan Liu and chemical industry Co., Ltd, has the purity of more than 99.5%;

4, 4' -difluorodiphenyl sulfone: the reaction monomer, Taiwan Liu and chemical industry Co., Ltd, has the purity of more than 99.5%;

4, 4' -biphenol: the reaction monomer, Taiwan Liu and chemical industry Co., Ltd, has the purity of more than 99.5%;

4, 4' -dihydroxydiphenyl sulfone: the reaction monomer, Jiangsu Aolandao scientific and technical actual company, the purity is more than 99.5%;

sodium carbonate: salt forming agent, Shandong Haihai chemical group Limited company, purity > 99.5%;

xylene: entrainers, isomerization grade, petrochemical, ltd, china;

glass fiber: CS910A-10P 4mm, Erwin Kening;

antioxidant: P-EPQ, Raine, Switzerland;

inorganic pigment: titanium white powder KRONOS R2233, knoss, germany.

The properties of the aromatic sulfone polymer, glass fiber reinforced composite of the examples of the present invention and the comparative example were measured according to the following test methods.

Aromatic sulfone polymers were tested as follows:

(1) testing the content of the phenolic end group: dissolving a polymer to be detected in dimethyl sulfoxide (DMSO), preparing a solution to be detected with a proper concentration (5-20 mg/mL), adding hydrochloric acid and a p-hydroxybenzoic acid (PHBA) internal standard substance, titrating with a tetrabutylammonium hydroxide solution in methanol, and determining an end point by a potential to obtain the total amount M of the phenolic end groups of the polymer solution. Weighing the same hydrochloric acid and PHBA, preparing a blank solution, testing the blank phenolic hydroxyl quantity M by potentiometric titration, and obtaining the phenolic end group content of the polymer by the difference (M-M) between the two.

(2) And (3) shear viscosity test: the test temperature is 380 ℃, the shear rate is 1000S < -1 >, a neck mold with the inner diameter of 1mm and the length of 40mm is used for measuring, and the shear viscosity change rate at different time are measured. The glass fiber reinforced composite was tested as follows:

(3) tensile strength: according to ISO 527-2: 2012, the test conditions are 23 ℃ and 10 mm/min.

(4) Bending strength: according to ISO 178: 2010 at 23 ℃ and 10 mm/min.

Examples 1 to 5 and comparative examples 1 to 2

The examples and comparative examples provide a series of polyphenylsulfone polymers and glass fiber reinforced composites prepared from polyphenylsulfone polymers. The preparation processes of the examples 1 to 4 and the comparative examples 1 to 3 are as follows:

(1) quantitatively adding 36kg of sulfolane, 8.787kg (30.6mol) of 4,4 '-dichlorodiphenyl sulfone and 5.586kg of 4, 4' -biphenol into a 100L reaction kettle protected by high-purity nitrogen, stirring, heating, adding 33kg (31.1mol) of sodium carbonate and 3kg of dimethylbenzene, keeping the temperature for 5 hours at 180-220 ℃ by adopting a solution polycondensation method, continuously discharging reaction water by azeotropic distillation of the dimethylbenzene in the reaction process until no water is discharged, finishing the salt forming reaction, and distilling out the dimethylbenzene. Then, the reaction system was heated to 235 ℃ and maintained for 1.5 hours. Adding 10kg of sulfolane into the system, keeping the temperature at 200 ℃, introducing methyl chloride gas, stopping introducing gas after 0.5h, and finishing polymerization. And precipitating the polymer material into strips in water, crushing the strips by a crusher to obtain a powdery material, boiling the powdery material for 1 hour by using deionized water, centrifugally filtering the powdery material, and repeating the step for 8 to 10 times until the filtrate does not become turbid when detected by using silver nitrate, namely the byproduct salt is washed out completely. And (3) removing water from the purified polymer under vacuum drying to obtain the polyphenylsulfone polymer.

(2) The resulting polyphenylsulfone polymer, glass fiber and antioxidant are blended as polyphenylsulfone polymer: glass fiber: antioxidant P-EPQ 79.95: 20:0.05 part of the mixture is blended and extruded in a double-screw extruder at the extrusion temperature of 350 ℃ and the rotation speed of 300rpm to obtain the glass fiber reinforced composite material.

Specifically, the flow rates of the methyl chloride gas introduced in examples 1 to 4 were 4.0L/min, 3.5L/min, 3.2L/min, and 2.8L/min, respectively. The flow rate of the methyl chloride gas introduced in comparative example 1 was 5.5L/min, and the flow rate of the methyl chloride gas introduced in comparative example 2 was 2.5L/min.

Example 5 and comparative examples 3 to 4

The present examples and comparative examples provide a series of glass fiber reinforced composites.

The glass fiber reinforced composite material provided in example 5 is prepared by the same method as in example 1 to obtain a polyphenylsulfone polymer, and the polyphenylsulfone polymer, the glass fiber and the antioxidant are mixed according to the following formula: glass fiber: and (3) blending 94.99:5:0.01 parts of antioxidant P-EPQ, extruding in a double-screw extruder at the extrusion temperature of 350 ℃ and the rotation speed of 300rpm, and extruding to obtain the glass fiber reinforced composite material.

The glass fiber reinforced composite materials provided by the comparative examples 3 and 4 are prepared into polyphenylsulfone polymers by the same method as that of the comparative example 1 and the comparative example 2 respectively, and the polyphenylsulfone polymers, the glass fibers and the antioxidant are prepared according to the following steps: glass fiber: and (3) blending 94.99:5:0.01 parts of antioxidant P-EPQ, extruding in a double-screw extruder at the extrusion temperature of 350 ℃ and the rotation speed of 300rpm, and extruding to obtain the glass fiber reinforced composite material.

Example 6 and comparative examples 5 to 6

The present examples and comparative examples provide a series of glass fiber reinforced composites.

The glass fiber reinforced composite material provided in example 6 is prepared by the same method as in example 1 to obtain a polyphenylsulfone polymer, and the polyphenylsulfone polymer, the glass fiber and the antioxidant are mixed according to the following formula: glass fiber: antioxidant P-EPQ 59.8: 40: 0.2 part of the mixture is blended and extruded in a double-screw extruder at the extrusion temperature of 350 ℃ and the rotation speed of 300rpm to obtain the glass fiber reinforced composite material.

The glass fiber reinforced composite materials provided by the comparative examples 5 and 6 are prepared by the same method as that of the comparative example 1 and the comparative example 2 respectively, and the obtained polyphenylsulfone polymer, the glass fiber and the antioxidant are mixed according to the weight ratio of polyphenylsulfone polymer: glass fiber: antioxidant P-EPQ 59.8: 40: 0.2 part of the mixture is blended and extruded in a double-screw extruder at the extrusion temperature of 350 ℃ and the rotation speed of 300rpm to obtain the glass fiber reinforced composite material.

Example 7

The present embodiment provides a polyphenylsulfone polymer and a glass fiber reinforced composite material prepared from the polyphenylsulfone polymer.

In the preparation method of the polyphenylsulfone polymer of this example, in step (1), the phenolic monomer used is not 4,4 '-biphenol, but 4, 4' -dihydroxydiphenylsulfone (7.508kg (30 mol)); the sulfone monomer was not 4,4 '-dichlorodiphenyl sulfone but 4, 4' -difluorodiphenyl sulfone (7.780kg (30.6mol)), and the rest was the same as in example 1.

In addition, the glass fiber reinforced composite material is obtained in the step (2) according to the same mixture ratio as in the embodiment 1.

Example 8

The embodiment provides a glass fiber reinforced composite material, wherein a polyphenylsulfone polymer is prepared by the same method as in embodiment 1, and the polyphenylsulfone polymer, glass fiber, antioxidant and titanium dioxide are prepared according to the following steps: glass fiber: antioxidant P-EPQ: and (3) blending 74.95:20:0.05:5 parts of titanium dioxide, extruding in a double-screw extruder at the extrusion temperature of 350 ℃ and the rotation speed of 300rpm, and extruding to obtain the glass fiber reinforced composite material.

The properties of the obtained aromatic sulfone polymer were measured in accordance with the above-mentioned methods, and the results are shown in tables 1 and 2.

TABLE 1 test results for examples 1-8

TABLE 2 test results for comparative examples 1 to 6

From table 1, it can be found that the glass fiber reinforced composite material provided by the embodiments of the present invention has excellent tensile strength and bending strength, and the mechanical properties are obviously improved. In examples 1 to 4 and comparative examples 1 to 2, the content of the phenolic terminal group of the polyphenylsulfone polymer changes with the flow of the end-capping reagent chloromethane, and the polyphenylsulfone polymer shows obvious regularity, that is, the content of the end-capping reagent is lower when the flow is larger, and meanwhile, the shear viscosity of the polyphenylsulfone polymer is kept consistent. While the tensile strength and bending strength of the polyphenylsulfone polymer are initially kept unchanged during the process of increasing the content of the phenolic terminal group from 30mol/t to 175mol/t, and after the content of the phenolic terminal group is 160mol/t (as in comparative example 2), the tensile strength and bending strength show a remarkable reduction trend, which may be attributed to that the thermal stability of the phenolic terminal group is relatively worse than that of the methoxy terminal group, and when the content of the phenolic terminal group is higher, the polymer terminal group is melted to a certain extent or the polymer is slightly degraded, so that the molecular weight is reduced and the mechanical properties are further worsened. Under the specific content of the phenol end group, namely when the content of the phenol end group is between 80 and 160mol/t, particularly between 115 and 135mol/t, the tensile strength and the bending strength of the 20 percent glass fiber reinforced composite material are improved by about 20 percent; the tensile strength and the bending strength of the glass fiber reinforced composite material under the rest mass fractions have similar rules. Therefore, the specific content of aromatic sulfone polymer described in the present invention is advantageous for the improvement of the performance of the glass fiber reinforced composite material.

It will be appreciated by those of ordinary skill in the art that the examples provided herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited examples and embodiments. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.